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Title: The Story of a Loaf of Bread
Author: Wood, Thomas Barlow
Language: English
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The Cambridge Manuals of Science and
Literature
THE STORY OF A LOAF OF BREAD
CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, MANAGER
[Illustration]
Edinburgh: 100, PRINCES STREET
London: H. K. LEWIS, 136, GOWER STREET, W.C.
WILLIAM WESLEY & SON, 28, ESSEX STREET, STRAND
Berlin: A. ASHER AND CO.
Leipzig: F. A. BROCKHAUS
New York: G. P. PUTNAM’S SONS
Bombay and Calcutta: MACMILLAN AND CO., Ltd.
_All rights reserved_
[Illustration:
THE STORY OF
A LOAF OF BREAD
BY
T. B. WOOD, M.A.
Drapers Professor of Agriculture
in the University of Cambridge
Cambridge:
at the University Press
New York:
G. P. Putnam’s Sons
1913]
Cambridge:
PRINTED BY JOHN CLAY, M.A.
AT THE UNIVERSITY PRESS
_With the exception of the coat of arms at the foot, the design on
the title page is a reproduction of one used by the earliest known
Cambridge printer, John Siberch, 1521_
PREFACE
I have ventured to write this little book with some diffidence, for it
deals with farming, milling and baking, subjects on which everyone has
his own opinion. In the earlier chapters I have tried to give a brief
sketch of the growing and marketing of wheat. If I have succeeded, the
reader will realise that the farmer’s share in the production of the
staple food of the people is by no means the simple affair it appears
to be. The various operations of farming are so closely interdependent
that even the most complex book-keeping may fail to disentangle the
accounts so as to decide with certainty whether or not any innovation
is profitable. The farmer, especially the small farmer, spends his days
in the open air, and does not feel inclined to indulge in analytical
book-keeping in the evening. Consequently, the onus of demonstrating
the economy of suggested innovations in practice lies with those who
make the suggestions. This is one of the many difficulties which
confronts everyone who sets out to improve agriculture.
In the third and fourth chapters I have discussed the quality of wheat.
I have tried to describe the investigations which are in progress with
the object of improving wheat from the point of view of both the farmer
and the miller, and to give some account of the success with which they
have been attended. Incidentally I have pointed out the difficulties
which pursue any investigation which involves the cultivation
on the large scale of such a crop as wheat, and the consequent
need of adopting due precautions to ensure accuracy before making
recommendations to the farmer. Advice based on insufficient evidence is
more than likely to be misleading. Every piece of misleading advice is
a definite handicap to the progress of agricultural science.
The fifth chapter is devoted to a short outline of the milling
industry. In chapter VI the process of baking is described. In the last
two chapters the composition of bread is discussed at some length. I
have tried to state definitely and without bias which points in this
much debated subject are known with some certainty, and which points
require further investigation.
Throughout the following pages, but especially in chapters III and IV,
I have drawn freely upon the work of my colleagues. I am also much
indebted to my friends, Mr A. E. Humphries, the chairman of the Home
Grown Wheat Committee, and Mr E. S. Beaven of Warminster, whose advice
has always been at my disposal. A list of publications on the various
branches of the subject will be found at the end of the volume.
T. B. W.
GONVILLE AND CAIUS COLLEGE,
CAMBRIDGE.
_3 December, 1912._
CONTENTS
CHAP. PAGE
Preface v
I. Wheat-growing 1
II. Marketing 15
III. The quality of wheat 27
IV. The quality of wheat from the miller’s point of view 51
V. The milling of wheat 74
VI. Baking 91
VII. The composition of bread 108
VIII. Concerning different kinds of bread 120
Bibliography 136
Index 139
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Typical ears of wheat 30
2. Bird-proof enclosure for variety testing 34
3. A wheat flower to illustrate the method of cross-fertilising 41
4. Parental types and first and second generation 43
5. Parent varieties in bird-proof enclosure 48
6. Testing new varieties in the field 50
7. Loaves made from Manitoba wheat 54
8. Loaves made from English wheat 54
9. Loaves made from Rivet wheat 55
10. Loaves made from Manitoba wheat, English wheat, and
Manitoba-English hybrid, Burgoyne’s Fife 59
11. Gluten in water and acid 69
12. Gluten in water containing both acid and salts 71
13. End view of break rolls 81
14. Break rolls showing gearing 82
15. Reduction rolls 87
16. Baking test: loaves rising in incubator 92
17. Baking test: loaves leaving the oven 93
THE STORY OF A LOAF OF BREAD
CHAPTER I
WHEAT GROWING
Wheat is one of the most adaptable of plants. It will grow on almost
any kind of soil, and in almost any temperate climate. But the question
which concerns the wheat grower is not whether he can grow wheat, but
whether he can grow it profitably. This is a question of course that
can never receive a final answer. Any increase in the price of wheat,
or any improvement that lowers the cost of cultivation, may enable
growers who cannot succeed under present conditions to grow wheat at
a profit. Thus if the population of the world increases, and wheat
becomes scarce, the wheat-growing area will doubtless be extended
to districts where wheat cannot be grown profitably under present
conditions. A study of the history of wheat-growing in this country
during the last century shows that the reverse of this took place.
In the first half of that period the population had increased, and
from lack of transport facilities and other causes the importation of
foreign wheat was small. Prices were high in consequence and every
acre of available land was under wheat. As transport facilities
increased wheat-growing areas were developed in Canada, in the
Western States of America, in the Argentine, and in Australia, and
the importation of foreign wheat increased enormously. This led to
a rapid decrease in prices, and wheat-growing had to be abandoned
on all but the most suitable soils in the British Isles. From 1880
onwards thousands of acres of land which had grown wheat profitably
for many years were laid down to grass. In the last decade the world’s
population has increased faster than the wheat-growing area has been
extended. Prices have consequently risen, and the area under wheat in
the British Isles will no doubt increase.
But although it cannot be stated with finality on what land wheat can
be grown, or cannot be grown, at a profit, nevertheless accumulated
experience has shown that wheat grows best on the heavier kinds of
loam soils where the rainfall is between 20 and 30 inches per annum.
It grows nearly as well on clay soils and on lighter loams, and with
the methods of dry farming followed in the arid regions of the Western
States and Canada, it will succeed with less than its normal amount of
rainfall.
It is now about a hundred years since chemistry was applied with any
approach to exactitude to questions affecting agriculture; since for
instance it was first definitely recognised that plants must obtain
from their surroundings the carbon, hydrogen, oxygen, nitrogen,
phosphorus, sulphur, potassium, calcium, and other elements of which
their substance is composed. For many years there was naturally much
uncertainty as to the source from which these several elements were
derived. Experiment soon showed that carbon was undoubtedly taken
from the air, and that its source was the carbon dioxide poured into
the air by fires and by the breathing of animals. It soon became
obvious too that plants obtain from the soil water and inorganic salts
containing phosphorus, sulphur, potassium, calcium, and so on; but
for a long time the source of the plants’ supply of nitrogen was not
definitely decided. Four-fifths of the air was known to be nitrogen.
The soil was known to contain a small percentage of that element, which
however amounts to four or five tons per acre. Which was the source
of the plants’ nitrogen could be decided only by careful experiment.
As late as 1840 Liebig, perhaps the greatest chemist of his day,
wrote a book on the application of chemistry to agriculture. In it he
stated that plants could obtain from the air all the nitrogen they
required, and that, to produce a full crop, it was only necessary to
ensure that the soil should provide a sufficient supply of the mineral
elements, as he called them, phosphorus, potassium, calcium, etc.
Now of all the elements which the farmer has to buy for application
to his land as manure, nitrogen is the most costly. At the present
time nitrogen in manures costs sevenpence per pound, whilst a pound
of phosphorus in manures can be bought for fivepence, and a pound
of potassium for twopence. The importance of deciding whether it is
necessary to use nitrogen in manures needs no further comment. It
was to settle definitely questions like this that John Bennet Lawes
began his experiments at his home at Rothamsted, near Harpenden in
Hertfordshire, on the manuring of crops. These experiments were started
almost simultaneously with the publication of Liebig’s book, and many
of Lawes’ original plots laid out over 70 years ago are still in
existence. The results which he obtained in collaboration with his
scientific colleague, Joseph Henry Gilbert, soon overthrew Liebig’s
mineral theory of manuring, and showed that in order to grow full crops
of wheat it is above all things necessary to ensure that the soil
should be able to supply plenty of nitrogen. Thus it was found that the
soil of the Rothamsted Experiment Station was capable of growing wheat
continuously year after year. With no manure the average crop was only
about 13 bushels per acre. The addition of a complete mineral manure
containing phosphorus, calcium, potassium, in fact all the plant wants
from the soil except nitrogen, only increased the crop to 15 bushels
per acre. Manuring with nitrogen on the other hand increased the crop
to 21 bushels per acre. Obviously on the Rothamsted soil wheat has
great difficulty in getting all the nitrogen it wants, but is well
able to fend for itself as regards what Liebig called minerals. This
kind of experiment has been repeated on almost every kind of soil in
the United Kingdom, and it is found that the inability of wheat to
supply itself with nitrogen applies to all soils, except the black
soils of the Fens which contain about ten times more nitrogen than the
ordinary arable soils of the country. It is the richness in nitrogen
of the virgin soils of the Western States and Canada, and of the black
soils of Russia, that forms one of the chief factors in their success
as wheat-growing lands. It must be added, however, that continuous
cropping without manure must in time exhaust the stores of nitrogen in
even the richest soil, and when this time comes the farmers in these
at present favoured regions will undoubtedly find wheat-growing more
costly by whatever sum per acre they may find it necessary to expend
in nitrogenous manure. The world’s demand for nitrogenous manure is
therefore certain to increase. Such considerations as these inspired
Sir William Crookes’ Presidential address to the British Association in
1898, in which he foretold the probability of a nitrogen famine, and
explained how it must lead to a shortage in the world’s wheat supply.
The remedy he suggested was the utilization of water-power to provide
the energy for generating electricity, by means of which the free
nitrogen of the air should be brought into combination in such forms
that it could be used for manure. It is interesting to note that these
suggestions have been put into practice. In Norway, in Germany, and in
America waterfalls have been made to drive dynamos, and the electricity
thus generated has been used to make two new nitrogenous manures,
calcium nitrate and calcium cyanamide, which are now coming on to the
market at prices which will compete with sulphate of ammonia from the
gas works, nitrate of soda from Chili, Peruvian guano, and the various
plant and animal refuse materials which have up to the present supplied
the farmer with his nitrogenous manures. This is welcome news to the
wheat grower, for the price of manurial nitrogen has steadily risen
during the last decade.
Before leaving the question of manuring one more point from the
Rothamsted experiments must be referred to. It has already been
mentioned that when manured with nitrogen alone the Rothamsted soil
produced 21 bushels of wheat per acre. When, however, a complete manure
containing both nitrogen and minerals was used the crop rose to 35
bushels per acre which is about the average yield per acre of wheat in
England. This shows that although the yield of wheat is dependent in
the first place on the nitrogen supplied by the soil, it is still far
from independent of a proper supply of minerals. A further experiment
on this point showed that minerals are not used up by the crop to which
they are applied, and that any excess left over remains in the soil
for next year. This is not the case with nitrogenous manures. Whatever
is left over from one crop is washed out of the soil by the winter
rains, and lost. Translated into farm practice these results mean that
nitrogenous manures should be applied direct to the wheat crop, but
that wheat may as a rule be trusted to get all the minerals it wants
from the phosphate and potash applied directly to other crops which are
specially dependent on an abundant supply of these substances.
At Rothamsted, Lawes and Gilbert adopted the practice of growing wheat
continuously on the same land year after year in order to find out
as quickly as possible the manurial peculiarities of the crop. This
however is not the general system of the British farmer, but it has
been carried out with commercial success by Mr Prout of Sawbridgeworth
in Hertfordshire. The Sawbridgeworth farm is heavy land on the London
clay. Mr Prout’s system was to cultivate the land by steam power, to
manure on the lines suggested by the Rothamsted experiments, and to
sell both grain and straw. Wheat was grown continuously year after year
until the soil became infested with weeds, when some kind of root crop
was grown to give an opportunity to clean the land. A root crop is not
sown until June so that the land is bare for cleaning all the spring
and early summer. Such crops also are grown in rows two feet or more
apart, and cultural implements can be used between the rows of plants
until the latter cover the soil by the end of July or August. After
cleaning the land in this way the roots are removed from the land in
the winter and used to feed the stock. By this time it is too late to
sow wheat, so a barley crop is sown the following spring, and with the
barley clover is sown. Clover is an exception to the rule that crops
must get their nitrogen from the soil.
On the roots of clover, and other plants of the same botanical order,
such as lucerne, sainfoin, beans and peas, many small swellings are
to be found. These swellings, or nodules as they are usually called,
are produced by bacteria which possess the power of abstracting free
nitrogen from the air and transforming it into combined nitrogen in
such a form that the clover or other host-plant can feed on it. The
clover and the bacteria live in Symbiosis, or in other words in a
kind of mutual partnership. The host provides the bacteria with a
home and allows them to feed on the sugar and other food substances
in its juices, and they in return manufacture nitrogen for the use of
the host. When the clover is cut for hay, its roots are left in the
soil, and in them is a large store of nitrogen derived from the air.
A clover crop thus enriches the soil in nitrogen and is the best of
all preparations for wheat-growing. After the clover, wheat was grown
again year after year until it once more became necessary to clean the
land. This system of wheat-growing was carried on at Sawbridgeworth
for many years with commercial success. It never spread through the
country because its success depends on the possibility of finding
a remunerative market for the straw. The bulk of straw is so great
compared with its price that it cannot profitably be carried to any
considerable distance. The only market for straw in quantity is a
large town, and there is no considerable area of land suitable for
wheat-growing near a sufficiently large town to provide a market for
the large output of straw which would result from such a system of
farming.
The ordinary practice of the British farmer is to grow his wheat in
rotation with other crops. Various rotations are practised to suit the
special circumstances of different districts, one might almost say of
special farms. This short account of wheat-growing does not profess to
give a complete account of even English farming practice. It is only
necessary to describe here one rotation in order to give a general
idea of the advantages of that form of husbandry. For this purpose
it will suffice to describe the Norfolk or four course rotation. This
rotation begins with a root crop, usually Swede turnips, manured with
phosphates, and potash too on the lighter lands. This crop, as already
described, provides the opportunity of cleaning the land. It produces
also a large amount of food for sheep and cattle. Part of the roots are
left on the land where they are eaten by sheep during the winter. The
roots alone are not suitable for a complete diet. They are supplemented
by hay and by some kind of concentrated food rich in nitrogen, usually
linseed cake, the residue left when the oil is pressed from linseed.
Now an animal only retains in its body about one-tenth of the nitrogen
of its diet, so that nine-tenths of the nitrogen of the roots, hay
and cake consumed by the sheep find their way back to the land. This
practice of feeding sheep on the land therefore acts practically as
a liberal nitrogenous manuring. The trampling of the soil in a wet
condition in the winter also packs its particles closely together, and
increases its water-holding power, in much the same way as the special
cultural methods employed in the arid western States under the name
of dry farming. The rest of the roots are carted to the homestead for
feeding cattle, usually fattening cattle for beef. Again the roots are
supplemented by hay, straw, and cake of some kind rich in nitrogen.
The straw from former crops is used for litter. Its tubular structure
enables it to soak up the excreta of the animals, so that the farmyard
manure thus produced retains a large proportion of the nitrogen, and
other substances of manurial value, which the animals fail to retain in
their bodies. This farmyard manure is kept for future use as will be
seen later.
As soon as the sheep have finished eating their share of the turnips
they are sold for mutton. It is now too late in the season to sow
wheat. The land is ploughed, but the ploughing is only a shallow one,
so that the water stored in the deeper layers of the soil which have
been solidified by the trampling of the sheep may not be disturbed. The
surface soil turned up by the plough is pulverised by harrowing until
a fine seed-bed is obtained, and barley is sown early in the spring.
Clover and grass seeds are sown amongst the barley, so that they may
take firm root whilst the barley is growing and ripening. The barley
is harvested in the autumn. The young clover and grasses establish
themselves during the autumn and winter, and produce a crop of hay the
following summer. This is harvested towards the end of June, and the
aftermath forms excellent autumn grazing for the sheep and cattle which
are to be fed the next winter.
As soon as harvest is over the farmer hopes for rain to soften the
old clover land, or olland as it is called in Norfolk, so that he can
plough it for wheat sowing. Whilst he is waiting for rain he takes
advantage of the solidity of the soil, produced by the trampling of the
stock, to cart on to the olland the farmyard manure produced during
the cattle feeding of the last winter. As soon as the rain comes this
is ploughed in, and the seed-bed for the wheat prepared as quickly
as possible. Wheat should be sown as soon as may be after the end of
September, so that the young plant may come up and establish itself,
while the soil is yet warm from the summer sun, and before the winter
frosts set in. The wheat spends the winter in root development, and
does not make much show above ground until the spring. It is harvested
usually some time in August. The wheat stubble is ploughed in the
autumn and again in the spring, and between then and June, when the
roots are sown, it undergoes a thorough cleaning.
The complete rotation has now been described. It remains only to point
out some of its numerous advantages. In the first place the system
described provides excellent conditions for growing both wheat and
barley in districts where the rainfall is inclined to be deficient,
say from 20 to 25 inches per annum, as it is in the eastern counties,
and on the Yorkshire wolds. Not only is an abundant supply of nitrogen
provided for these crops through the medium of the cake purchased for
the stock, but the solidification of the deeper layers of the soil
ensures the retention of the winter’s rain for the use of the crop
during the dry summer. The residue of the phosphates and potash applied
to the root crop, and left in the soil when that crop is removed,
provides for the mineral requirements of the barley and the wheat.
Thus each crop gets a direct application of the kind of manure it most
needs. Rotation husbandry also distributes the labour of the farm over
the year. After harvest the farmyard manure is carted on to the land.
This is followed by wheat sowing. In the winter there is the stock to
be fed. The spring brings barley sowing, the early summer the cleaning
of the land for the roots. Then follow the hay harvest and the hoeing
of the roots, and by this time corn-harvest comes round once again.
It must not be forgotten that each crop the farmer grows is subject to
its own pests. On a four course rotation each crop comes on the same
field only once in four years. Whilst the field is under roots, barley,
and clover, the wheat pests are more or less starved for want of food,
and their virulence is thereby greatly diminished. The catalogue of
the advantages of rotation of crops is a long one but one more must be
mentioned. The variety of products turned out for sale by the rotation
farmer ensures him against the danger which pursues the man who puts
all his eggs in one basket. The four course farmer produces not only
wheat and barley, but beef and mutton. The fluctuations in price of
these products tend to compensate each other. When corn is cheap,
meat may be dear, and vice versâ. Thus in the years about 1900, when
corn was making very low prices, sheep sold well, and the profit on
sheep-feeding enabled many four course farmers to weather the bad times.
The system of wheat-growing above described is an intensive one.
The cultivation is thorough, the soil is kept in good condition by
manuring, or by the use of purchased feeding stuffs, and the cost of
production is comparatively high. Such systems of intensive culture
prevail in the more densely populated countries, but the bulk of the
world’s wheat supply is grown in thinly populated countries, where
the methods of cultivation are extensive. Wheat is sown year after
year on the same land, no manure is used, and tillage is reduced to a
minimum. This style of cultivation gradually exhausts the fertility of
the richest virgin soil, and its cropping capacity falls off. As soon
as the crop falls below a certain level it ceases to be profitable. No
doubt the fertility of the exhausted soil could be restored by suitable
cultivation and manuring, but it is usually the custom to move towards
districts which are still unsettled, and to take up more virgin soil.
Thus the centre of the area of wheat production in the States has moved
nearly 700 miles westward in the last 50 years.
CHAPTER II
MARKETING
In the last chapter we have followed the growing of the wheat from
seed time to harvest. But when the farmer has harvested his corn his
troubles are by no means over. He has still to thrash it, dress it,
sell it, and deliver it to the mill or to the railway station. In the
good old times a hundred years ago thrashing was done by the flail,
and found work during the winter for many skilled labourers. This
time-consuming method has long disappeared. In this country all the
corn is now thrashed by machines, driven as a rule by steam, but still
in some places by horse-gearing. The thrashing machine, like all other
labour saving devices, when first introduced was bitterly opposed by
the labourers, who feared that they might lose their winter occupation
and the wages it brought them. In the life of Coke of Norfolk, the
first Lord Leicester, there is a graphic account of the riots which
took place when the first thrashing machine was brought into that
county.
Only the larger farmers possess their own machines. The thrashing on
the smaller farms is done by machines belonging to firms of engineers,
which travel the country, each with its own team of men. These
machines will thrash out more than 100 bags of wheat or barley in a
working day. The more modern machines dress the corn so that it is
ready for sale without further treatment. After it is thrashed the
wheat is carried in sacks into the barn and poured on to the barn
floor. It is next winnowed or dressed, again by a machine, which
subjects it to a process of sifting and blowing in order to remove
chaff, weed-seeds and dirt. As it comes from the dressing machine it is
measured into bags, each of which is weighed and made up to a standard
weight ready for delivery. In the meantime the farmer has taken a
sample of the wheat to market. The selling of wheat takes place on
market day in the corn hall, or exchange, with which each market town
of any importance is provided. In the hall each corn merchant in the
district rents a small table or desk, at which he stands during the
hour of the market. The farmer takes his sample from one merchant to
another and sells it to the man who offers him the highest price. The
merchant keeps the sample and the farmer must deliver wheat of like
quality. In the western counties it is sometimes customary for the
farmers to take their stand near their sample bags of corn whilst the
merchants walk round and make their bids.
But unfortunately it too often happens that the struggling farmer
cannot have a free hand in marketing his corn. In many cases he must
sell at once after harvest to raise the necessary cash to buy stock
for the winter’s feeding. This causes a glut of wheat on the market
in the early autumn, and the price at once drops. In other cases the
farmer has bought on credit last winter’s feeding stuffs, or last
spring’s manures, and is bound to sell his wheat to the merchant in
whose debt he finds himself, and to take the best price offered in a
non-competitive market.
These are by no means all the handicaps of the farmer who would market
his corn to the best advantage. Even the man who is blessed with plenty
of ready money, and can abide his own time for selling his wheat, is
hampered by the cumbrous weights and measures in use in this country,
and above all by their lack of uniformity. In East Anglia wheat is sold
by the coomb of four bushels. By common acceptance however the coomb
has ceased to be four measured bushels, and is always taken to mean 18
stones or 2¼ cwt. This custom is based on the fact that a bushel of
wheat weighs on the average 63 pounds, and four times 63 pounds makes
18 stones. But this custom is quite local. In other districts the unit
of measure for the sale of wheat is the load, which in Yorkshire means
three bushels, in Oxfordshire and Gloucestershire 40 bushels, and in
parts of Lancashire 144 quarts. Another unit is the boll, which varies
from three bushels in the Durham district to six bushels at Berwick.
It will be noted that most of the common units are multiples of the
bushel, and it might be imagined that this would make their mutual
relations easy to calculate. This however is not so, for in some cases
it is still customary to regard a bushel as a measure of volume and to
disregard the variation in weight. In other cases the bushel, as in
East Anglia, means so many pounds, but unfortunately not always the
same number. Thus the East Anglian bushel is 63 pounds, the London
bushel on Mark Lane Market is the same, the Birmingham bushel is only
62 pounds, the Liverpool and Manchester bushel 70 pounds, the Salop
bushel 75 pounds, and in South Wales the bushel is 80 pounds. Finally,
wheat is sold in Ireland by the barrel of 280 pounds, on Mark Lane by
the quarter of eight bushels of 63 pounds, imported wheat in Liverpool
and Manchester by the cental of 100 pounds, and the official market
returns issued by the Board of Agriculture are made in bushels of 60
pounds. There is, however, a growing tendency to adopt throughout the
country the 63 pound bushel or some multiple thereof, for example the
coomb or quarter, as the general unit, and the use of the old-fashioned
measures is fast disappearing.
The farmer of course knows the weights and measures in use in his own
and neighbouring markets, but unless he takes the trouble to look
up in a book of reference the unit by which wheat is sold at other
markets, and to make a calculation from that unit into the unit in
which he is accustomed to sell, the market quotations in the newspapers
are of little use to him in enabling him to follow the fluctuations
of the price of wheat. Thus a Norfolk farmer who wishes to interpret
the information that the price of the grade of wheat known as No. 4
Manitoba on the Liverpool market is 7/3½, must first ascertain that
wheat is sold at Liverpool by the cental of 100 pounds. To convert
the Liverpool price into price per coomb, the unit in which he is
accustomed to sell, he must multiply the price per cental by 252, the
number of pounds in a coomb of wheat, and divide the result by 100, the
number of pounds in a cental; thus:
7/3½ x 252 ÷ 100 = 18/4½.
It is evident that the farmer who wishes to follow wheat prices in
order to catch the best market for his wheat, must acquaint himself
with an extremely complicated system of weights and measures, and
continually make troublesome calculations. The average English farmer
is an excellent craftsman. He is unsurpassed, indeed one may safely say
unequalled, as a cultivator of the land, as a grower of crops, and as
a breeder and feeder of stock, but like most people who lead open-air
lives, he is not addicted to spending his evenings in arithmetical
calculations. The corn merchant, whose business it is to attend to
such matters, is therefore at a distinct advantage, and the farmer
loses the benefit of a rise in the market until the information slowly
filters through to him. No doubt the time will come, when not only
wheat selling, but all business in this country, will be simplified by
the compulsory enactment of sale by uniform weight. The change from
the present haphazard system or want of system would no doubt cause
considerable temporary dislocation of business, and would abolish many
ancient weights and measures, interesting to the historian and the
archaeologist in their relations to ancient customs, but in the long
run it could not but expedite business, and remove one of the many
handicaps attaching to the isolated position of the farmer.
Having sold his wheat the farmer now puts it up in sacks of the
standard of weight or measure prevailing in his district. If the
merchant who bought it happens to be also a miller, as is frequently
the case, the wheat is delivered to the mill. Otherwise it is sent
to the railway station to the order of the merchant who bought
it. Meantime the merchant has probably sold it to a miller in a
neighbouring large town, to whom he directs the railway company to
forward it. Thus the wheat directly or indirectly finds its way to a
mill, where it will be mixed with other wheats and ground into flour.
We have now followed wheat production in England from the ground to
the mill. But at the present time home grown wheat can provide only
about one-fifth of the bread-stuffs consumed by the population of
the United Kingdom, and any account of the growing of wheat cannot
be complete without some mention of the methods employed in other
countries. The extensive methods of wheat-growing in the more thinly
populated countries have already been shortly mentioned. But though
their methods of production are of the simplest, the arrangements for
marketing their produce are far more advanced in organisation than
those already described for the marketing of home grown produce.
For thrashing in Canada and the Western States, travelling machines
are commonly used, but they are larger than the machines in use in
this country, and the men who travel with them work harder and for
longer hours. It is usual for a Canadian travelling “outfit” to thrash
1000 bags of wheat in a day, about ten times as much as is considered
a day’s thrashing in England. Harvesting and thrashing machinery has
evolved to an extraordinary extent in the West on labour saving lines.
On the Bonanza farms of the Western States machines are in use which
cut off the heads of the wheat, thrash out the seed, and bag it ready
for delivery, as they travel round and round the field. Such machines
of course leave the straw standing where it grew, and there it is
subsequently burnt. Since wheat is grown every year, few animals are
kept beyond the working horses. Very little straw suffices for them and
the rest has no value since its great bulk prohibits its profitable
carriage to a distance.
After being thrashed the grain is delivered, usually in very large
loads drawn by large teams of horses, to the nearest railway station,
whence it is despatched to the nearest centre where there is a grain
store, or elevator as it is called. Here it is sampled by inspectors
under the control, either of the Government or the Board of Trade, as
the committee is called which manages the wheat exchange at Chicago
or other of the great wheat trading centres. The inspectors examine
the sample, and on the result of their examination, assign the wheat
to one or other of a definite series of grades. These grades are
accurately defined by general agreement of the Board of Trade or by
the Government. Each delivery of wheat is kept separate for a certain
number of days after it has been graded, in case the owner wishes to
appeal against the verdict of the inspector. Such appeals are allowed
on the owner forfeiting one dollar per car load of grain if the verdict
of the inspector is found to have been correct. At the Chicago wheat
exchange 27 grades of wheat are recognised. The following examples show
the methods by which they are defined. The definitions are the subject
of frequent controversy.
No. 1 Northern Hard Spring Wheat shall be sound, bright, sweet, clean,
and shall consist of over 50 per cent. of hard Scotch Fife, and weigh
not less than 58 pounds to the measured bushel.
No. 1 Northern Spring Wheat shall be sound, sweet and clean; may
consist of hard and soft varieties of spring wheat, but must contain
a larger proportion of the hard varieties, and weigh not less than 57
pounds to the measured bushel.
No. 2 Northern Spring Wheat shall be spring wheat not clean enough or
sound enough for No. 1, but of good milling quality, and must not weigh
less than 56 pounds to the measured bushel.
No. 3 Northern Spring Wheat shall be composed of inferior shrunken
spring wheat, and weigh not less than 54 pounds to the measured bushel.
No. 4 Northern Spring Wheat shall include all inferior spring wheat
that is badly shrunken or damaged, and shall weigh not less than 49
pounds to the measured bushel.
When sampling wheat for grading, the inspectors also estimate the
number of pounds of impurities per bushel, a deduction for which is
made under the name of dockage. At the same time the weight of wheat in
each car is officially determined. All these points, grade, dockage,
and weight, are officially registered, and as soon as the time has
elapsed for dealing with any appeal which may arise, the wheat is
mixed with all the other wheats of the same grade which may be at
the depot, an official receipt for so many bushels of such and such a
grade of wheat subject to so much dockage being given to the seller or
his agent. These official receipts are as good as cash, and the farmer
can realise cash on them at once by paying them into his bank, without
waiting for the wheat to be sold.
As each delivery of wheat is graded and weighed, word is sent to
the central wheat exchanges that so many bushels of such and such
grades are at the elevator, and official samples are also sent on
at the same time. The bulk of the sales however are made by grade
and not by sample. The actual buying and selling takes place in the
wheat exchanges, or wheat pits as they are called, at Chicago, New
York, Minneapolis, Duluth, Kansas City, St Louis, and Winnipeg, each
of which markets possesses its own special character. Chicago the
greatest of the wheat markets of the world passes through its hands
every year about 25 million bushels of wheat, chiefly from the western
and south-western States. It owes its preeminence to the converging
railway lines from those States, and to its proximity to Lake Michigan
which puts it in touch with water carriage. New York has grown in
importance as a wheat market since the opening of the Erie Canal. It
is especially the market for export. Minneapolis is above all things
a milling centre. No doubt it has become so partly on account of the
immense water-power provided by the Falls of St Antony. It receives
annually nearly 100 million bushels of wheat, its speciality being the
various grades of hard spring wheat. Duluth is the most northern of the
American wheat markets. It receives and stores over 50 million bushels
annually. It owes its importance to its position on Lake Superior,
which is available for water carriage. Kansas City deals with over 40
million bushels per annum, largely hard winter wheat, which it ships
down the Missouri River. St Louis deals in soft winter wheats to the
extent of about 20 million bushels per annum. Winnipeg is the market
for Canadian wheats, to the extent of over 50 million bushels per
annum. It has the advantage of two navigable rivers, the Red River and
the Assiniboine, and it is also a great railway centre. Its importance
is increasing as the centre of the wheat-growing area moves to the
north and west, and it is rapidly taking the leading position in the
wheat markets of the world.
It has been stated above that Chicago is the greatest wheat market,
but it will no doubt have been noticed that this is not borne out by
the figures which have been quoted. For instance, Minneapolis receives
every year nearly four times as much wheat as Chicago. The reason of
this apparent discrepancy is that the sales at Minneapolis are really
_bona fide_ sales of actual wheat for milling, whilst nine-tenths
of the sales at Chicago are not sales of actual wheat, but of what
are known as “futures.” On this assumption, whilst the actual wheat
received at Chicago is 25 million bushels, the sales amount to 250
million bushels. Such dealing in futures takes place to a greater or
less extent at all the great wheat markets, but more at Chicago than
elsewhere.
The primary reason for dealing in futures is that the merchant who
buys a large quantity of wheat, which he intends to sell again at some
future time, may be able to insure himself against loss by a fall
in price whilst he is holding the wheat he has bought. This he does
by selling to a speculative buyer an equal quantity of wheat to be
delivered at some future time. If whilst he is holding his wheat prices
decline, he will then be able to recoup his loss on the wheat by buying
on the market at the reduced price now current to meet his contract
with the speculative buyer, and the profit he makes on this transaction
will more or less cover his loss on the actual deal in wheat which
he has in progress. As a matter of fact he does not actually deliver
the wheat sold to the speculative buyer. The transaction is usually
completed by the speculator paying to the merchant the difference in
value between the price at which the wheat was sold and the price to
which it has fallen in the interval. This payment is insured by the
speculative buyer depositing a margin of so many cents per bushel at
the time when the transaction was made. Speculation is, however, kept
within reasonable bounds by the fact that a seller may always be called
upon to deliver wheat instead of paying differences.
The advantage claimed for this system of insurance is that whilst
it is not more costly to the dealers in actual wheat than any other
equally efficient method, it supports a number of speculative buyers
and sellers, whose business it is to keep themselves in touch with
every phase of the world’s wheat supply. The presence of such a body of
men whose wits are trained by experience of market movements, and who
are ready at any moment to back their judgment by buying and selling
large quantities of wheat for future delivery, is considered to exert
a steadying effect on the price of wheat, and to lessen the extent of
fluctuations in the price.
CHAPTER III
THE QUALITY OF WHEAT
In discussing the quality of wheat it is necessary to adopt two
distinct points of view, that of the farmer and that of the miller. A
good wheat from the farmer’s point, of view is one that will year by
year give him a good monetary return per acre. Now the monetary return
obviously depends on two factors, the yield per acre and the value per
quarter, coomb, or bushel, as the case may be. These two factors are
quite independent and must be discussed separately.
We will first confine our attention to the yield per acre. This has
already been shown to depend on the presence in the soil of plenty of
the various elements required by plants, in the case of wheat nitrogen
being especially important. The need of suitable soil and proper
cultivation has also been emphasised. These conditions are to a great
extent under the control of the farmer, whose fault it is if they
are not efficiently arranged. But there are other factors affecting
the yield of wheat which cannot be controlled, such for instance as
sunshine and rainfall. The variations in these conditions from year to
year are little understood, but they are now the subject of accurate
study, and already Dr W. N. Shaw, the chief of the Meteorological
Office has suggested a periodicity in the yield of wheat, connected
with certain climatic conditions, notably the autumnal rainfall.
We have left to the last one of the most important factors which
determine the yield of wheat, namely, the choice of the particular
variety which is sown. This is undoubtedly one of the most important
points in wheat-growing which the farmer has to decide for himself.
The British farmer has no equal as a producer of high class stock. He
supplies pedigree animals of all kinds to the farmers of all other
lands, and he has attained this preeminence by careful attention to
the great, indeed the surpassing, importance of purity of breed. It
is only in recent years that the idea has dawned on the agricultural
community that breed is just as important in plants as in animals. It
is extraordinary that such an obvious fact should have been ignored
for so long. That it now occupies so prominently the attention of the
farmers is due to the work of the agricultural colleges and experiment
stations in Sweden, America, and many other countries, and last but
by no means least in Great Britain. This demonstration of the value
of plant breeding is perhaps the greatest achievement in the domain
of agricultural science since the publication of Lawes and Gilbert’s
classical papers on the manurial requirements of crops.
Wheat is not only one of the most adaptable of plants. It is also one
of the most plastic and prone to variation. During the many centuries
over which its cultivation has extended it has yielded hundreds of
different varieties, whose origin, however, except in a few doubtful
cases is unknown. Comparatively few of these varieties are in common
use in this country, and even of these it was impossible until recently
to say which was the best. It was even almost impossible to obtain
a pure stock of many of the standard varieties. This is by no means
the simple matter it appears to be. It is of course quite easy to pick
out a single ear, to rub out the grain from it, to sow the grain on a
small plot by itself and to raise a pound or so of perfectly pure seed.
This can again be sown by itself, and the produce, thrashed by hand,
will give perhaps a bushel of seed which will be quite pure. From this
seed it will be possible to sow something like an acre; and now the
trouble begins. Any kind of hand thrashing is extremely tedious for the
produce of acre plots, and thrashing by machinery becomes imperative.
Now a thrashing machine is an extremely complicated piece of apparatus,
which it is practically impossible thoroughly to clean. When once seed
has been through such a machine it is impossible to guarantee its
purity. Contamination in the thrashing machine is usually the cause of
the impurity of the stocks of wheat and other cereals throughout the
country. The only remedy is for the farmer to renew his stock from time
to time from one or other of the seedsmen or institutions who make it
their business to keep on hand pure stocks obtained by the method above
described.
[Illustration: Fig. 1. Typical ears of a few of the many cultivated
varieties of wheat]
Comparative trials of pure stocks of many of the standard varieties
of wheat, and of the other cereals, are being carried out in almost
every county by members of the staff of the agricultural colleges.
The object of such trials is to determine the relative cropping power
of the different varieties. This might at first sight appear to be
an extremely simple matter, but a moment’s consideration shows that
this is not the case. No soil is so uniform that an experimenter can
guarantee that each of the varieties he is trying has the same chance
of making a good yield as far as soil is concerned. It is a matter of
common knowledge too that every crop of wheat is more or less affected
by insect and fungoid pests, whose injuries are unlikely to fall
equally on each of the varieties in any variety test. Many other causes
of variation, such as unequal distribution of manure, inequalities in
previous cropping of the land, irregular damage by birds, may well
interfere with the reliability of such field tests.
Much attention has been given to this subject during the last few
years, and it has been shown that as often as not two plots of the
same variety of wheat grown in the same field under conditions which
are made as uniform as possible will differ in yield by 5 per cent. or
more. Obviously it is impossible to make comparisons of the cropping
power of different varieties of wheat as the result of trials in
which single plots of each variety are grown. It is a deplorable fact
however that the results of most of the trials which are published are
based on single plots only of the varieties compared. Such results
can have no claim to reliability. Single plots tests are excellent
as local demonstrations, to give the farmers a chance of seeing the
general characters of the various wheats in the field, but for the
determination of cropping power their results are misleading. For
the comparison of two varieties however an accuracy of about 1 per
cent., which is good enough for the purpose in view, can be obtained
by growing, harvesting and weighing separately, five separate plots of
each variety under experiment, provided the plots are distributed in
pairs over the experimental field.
Still greater accuracy can be attained by growing very large numbers
of very small plots of each variety in a bird-proof enclosure. The
illustration shows such an enclosure at Cambridge where five varieties
were tested, each on 40 plots. Each plot was one square yard, and the
whole 200 plots occupied so small an area that uniformity of soil could
be secured by hand culture.
Several experimenters are now at work on these lines, and it is to be
hoped that all who wish to carry out variety tests will either follow
suit, or content themselves with using their single plots only for
demonstrating the general characters of the varieties in the field.
So far we have confined our discussion to the standard varieties, and
we must now turn our attention to the work which has been done in
recent years on the breeding of new varieties which will yield heavier
crops than any of the varieties hitherto in cultivation.
[Illustration: Fig. 2. Part of bird-proof enclosure containing many
small plots for variety testing]
It is impossible to give more than a very brief outline of the vast
amount of work which has been done on this subject. Broadly speaking,
two methods have been used, selection and hybridisation. Of these
selection is the simpler, but even selection is by no means the simple
matter it might appear to be. Let us examine for a moment the various
characters of a single wheat plant which determine its capacity for
yielding grain. The average weight of one grain, the number of grains
in an ear, the number of ears on the plant, are obviously all of them
characters which will influence the weight of grain yielded by the
plant. Many experimenters have examined thousands of plants for these
characters, often by means of extremely ingenious mechanical sorting
instruments, and have raised strains of seed from the plants showing
one or more of these characters in the highest degree. The results of
this method of selection have as a rule been unsuccessful, no doubt
because the size of the grain, the number of grains in the ear, and
the number of ears on the plant, are so largely determined by the food
supply, or by some other cause quite outside the plant itself. They are
in fact in most cases acquired characters, and are not inherited. This
method of selection results in picking out rather the well nourished
plant than the well bred one. Again it is obvious that the weight of
grain per acre is measured by the weight of one grain, multiplied by
the number of grains per ear, multiplied by the number of ears per
plant, multiplied by the number of plants per acre. Selecting for any
one of these characters, say large ears, is quite likely to diminish
other equally important characters, say number of ears per plant.
In order to avoid these difficulties the method of selection according
to progeny has been devised. The essence of this method is to select
for stock, not the best individual plant, but the plant whose progeny
yields the greatest weight of seed per unit area. This method was
applied with great industry and some success in the Minnesota wheat
breeding experiments of Willett Hays. Large numbers of promising plants
were collected from a plot of the best variety in that district. The
seed from each plant was rubbed out and sown separately. One hundred
seeds from each plant were sown on small separate plots which were
carefully marked out and labelled. Every possible precaution was taken
to make all the little plots uniform in every way. By harvesting each
plot separately, and weighing the grain it produced, it was possible to
find out which of the original plants had given the largest yield. This
process was repeated by sowing again on separate plots a hundred seeds
from each individual plant from the best plot, and again weighing the
produce of each plot. After several repetitions it was stated that new
strains were obtained which yielded considerably greater crops than the
variety from which they were originally selected. These results were
published in 1895, but no definite statements have since appeared as to
the success ultimately attained.
This method of selection is undoubtedly more likely to give successful
results than the method which depends on the selection of plants for
their apparent good qualities; but it has several weak points. In
the first place it is almost impossible to make the soil of a large
number of plots so uniform that variation in yield due to varying soil
conditions will not mask the variations due to the different cropping
power of the seed of the separate plants. Many experimenters are still
at work with a view to overcome this difficulty. Secondly, plant
breeders are by no means agreed on the exact theoretical meaning of
improvement by selection. The balance of evidence at the present time
seems to tend towards the general adoption of what is known as the
pure-line theory. According to this theory, which was first enunciated
by Johannsen of Copenhagen as the outcome of a lengthy series of
experiments with beans, the general population of plants, in say a
field of wheat of one of the standard varieties giving an average
yield of say 40 bushels per acre, consists of a very large number of
races each varying in yielding capacity from say 30 to 50 bushels per
acre. These races can be separated by collecting a very large number
of separate plants, sowing say 100 seeds from each on a separate plot,
and weighing the produce separately. The crop on each plot, being the
produce of a separate plant, will be a distinct race, or pure line
as it is called, and each pure line will possess a definite yielding
power of its own. If this is so the difficulty of soil variation can be
overcome by saving seed from many of the best plots, and sowing it on
several separate plots. At harvest time these are gathered separately
and weighed. By averaging the weights of grain from many separate plots
scattered over the experimental area the effect of soil variation can
be eliminated.
The method is very laborious, but seems to promise successful results.
For instance, Beaven of Warminster, working on these lines, has
succeeded in isolating a pure line of Archer barley which is a distinct
advance on the ordinary stocks of that variety. There appears to be
no reason why it should not be applied to wheat with equal success;
in fact, Percival of Reading states that his selected Blue Cone wheat
was produced in this way. The essence, of the method is that if the
pure-line theory holds there is no necessity to continue selecting
the best individual plant from each plot, for each plot being the
produce of a single plant must be a pure line with its own definite
characters. The whole of the seed from a number of the best plots can
therefore be saved. The seed from each of these good plots can be used
to sow many separate plots: by averaging the yields from these plots
the effects of soil variation can be eliminated, and the cropping
power thus determined with great accuracy. It is thus possible to
pick out the best pure line with far greater certainty than in any
other way. It must not be forgotten, however, that the success of the
method depends on the truth of the pure-line theory. It should also
be pointed out that the cereals are all self-fertilised plants. When
working on these lines with plants which are readily cross-fertilised,
such for instance as turnips or mangels, it is necessary to enclose the
original individual plants, and the subsequent separate plots, so as to
prevent them from crossing with plants of other lines, in which case
the progeny would be cross-bred and not the progeny of a single plant.
This of course enormously increases the difficulty of carrying out the
experiment. Enough has been said to show that the task of improving
plants by systematic selection is an extremely tedious and difficult
one. Of course anyone may be fortunate enough to drop on a valuable
sport when carefully inspecting his crops, and it appears likely that
many of the most valuable varieties in cultivation have originated from
lucky chances of this kind.
It has always been the dream of the plant breeder to make use of the
process of hybridisation for creating new varieties, but until the
work of Mendel threw new light on the subject the odds were against
the success of the breeder. The idea of the older hybridisers was that
crossing two dissimilar varieties broke the type and gave rise to
greatly increased variation. From the very diverse progeny resulting
from the cross, likely individuals were picked out. Seed was saved from
these and sown on separate plots, and attempts were made to obtain a
fixed type by destroying, or roguing as it is called, all the plants
which departed from the desired type. This was a tedious process which
seldom resulted in success. Mendel’s discoveries, made originally
nearly 50 years ago, as the result of experiments in the garden of
his monastery, in the crossing of different varieties of garden peas,
remained unknown until rediscovered in 1899. In the 12 years which
have elapsed since that date the results which have been achieved show
clearly that the application of Mendelian methods is likely greatly
to increase the simplicity and the certainty of plant improvement by
hybridisation.
[Illustration: Fig. 3. A wheat flower with the chaff opened to show the
stamens and the stigmas]
Perhaps the best way of describing the bearing of Mendel’s Laws on the
improvement of wheat is to give an illustration from the work carried
out by Biffen at Cambridge, dealing at first with simple characters
obvious to anyone. In one of his first experiments two varieties of
wheat were crossed with each other. The one variety possessed long
loose beardless ears, the other short dense bearded ears. The crossing
was performed early in June, sometime before what the farmer calls
flowering time. The flowering of wheat as understood by the farmer
is the escape of the stamens from the flower. Fertilisation always
takes place before this, and crossing must be done of course before
self-fertilisation has been effected. The actual crossing is done
thus: An ear of one of the varieties having been chosen, one of the
flowers is exposed by opening the chaff which encloses it (Fig. 3),
the stamens are removed by forceps, and a stamen from a flower of the
other variety is inserted, care being taken that it bursts so that
the pollen may touch the feathery stigmas. The chaff is then pushed
back so that it may protect the flower from injury. The pollen grains
grow on the stigmas, and penetrate down the styles into the ovary. In
this way cross-fertilisation is effected. It is usual to operate on
several flowers on an ear in this way, and to remove the other flowers,
so that no mistake may be made as to which seed is the result of the
cross. Immediately after the operation the ear is usually tied up in
a waxed paper bag. This serves to make it absolutely certain that
no other pollen can get access to the stigmas except that which was
placed there. At the same time it is a convenient way of marking the
ear which was experimented upon. The cross is usually made both ways,
each variety being used both as pollen parent and as ovary parent.
As soon as the cross-fertilised seeds are ripe they are gathered, and
early in the autumn they are sown. It is almost necessary to sow them
and other small quantities of seed wheat in an enclosure protected by
wire netting. Otherwise they are very liable to suffer great damage
from sparrows. The plants which grow from the cross-fertilised seeds
are known as the first generation. In the case under consideration,
they were found to produce ears of medium length and denseness,
intermediate between the ears of the two parent varieties, and to be
beardless. The first generation plants were also characterised by
extraordinary vigour, as is the case with almost all first crosses,
both in plants and animals. Their seed was saved and sown on a small
plot, and produced some hundreds of plants of the second generation.
On examining these second generation plants it was found that the
characters of the parent varieties had rearranged themselves in every
possible combination, long ears with and without beard, short ears with
and without beard, intermediate ears with and without beard, as shown
in Fig. 4. These different types were sorted out and counted, when they
were found to be present in perfectly definite proportions. This is
best shown in the form of a tabulated statement, thus:
Ears Ears Ears Ears Ears Ears
Long Long Medium Medium Short Short
Beardless Bearded Beardless Bearded Beardless Bearded
3 1 6 2 3 1
Translating this into words, out of every 16 plants in the second
generation there were four long eared plants, three beardless and one
bearded; eight plants with ears of intermediate length, six beardless
and two bearded; and four short eared plants, three beardless and one
bearded. The illustration shows all these types. The experiment has
been repeated several times and the same proportions were invariably
obtained. The result, too, was independent of the way the cross was
made. Seed was collected separately from large numbers of single
plants of each type. The seed from each plant was sown by itself
in a row, so that its progeny could be separately observed. It was
found that all the plants of the second generation possessing ears of
intermediate length produced in the third generation plants with long
ears, short ears, and medium ears in the proportion of 1 : 1 : 2, the
same proportion in fact as in the second generation. Short eared plants
produced only short eared offspring, long eared plants only long eared
offspring. Bearded plants produced only bearded offspring. Beardless
plants, however, produced in some cases only beardless offspring, in
other cases both beardless and bearded offspring in the proportion of
three of the former to one of the latter. Out of every three beardless
plants only one was found to breed true, whilst two gave a mixed
progeny. It appears therefore that in the second generation some of the
types which occur breed true, whilst others do not. Some of the true
breeding individuals can be picked out at sight, for instance, those
with long or short bearded ears. Some of those which will not breed
true can also be recognised by inspection, for instance, all the plants
with ears of intermediate length. In other cases it is only possible to
pick out the individual plants which breed true by growing their seed
and observing how it behaves. If it produces progeny all of which are
like the plant from which the seed was obtained, that plant is a fixed
type and will breed true continuously in the future. The final result
of the experiment was to obtain in three years from the time the cross
was made, four fixed types which subsequent experience has shown breed
true continuously, a long eared bearded type, a short eared beardless
type, a long eared beardless type and a short eared bearded type. Of
these the second two are exactly like the two parental varieties, but
the first two are new, each combining one character from each parent.
These fixed types already existed in the second generation. Mendel’s
discoveries with peas showed how to pick them out. Obviously there is
no need for the years of roguing by which the older hybridisers used
to attempt to fix their desired type. All the types are present in the
second generation. Mendel has shown how the fixed ones may be picked
out.
[Illustration: Fig. 4. _P_, _P_, the two parental types. _F₁_ the first
cross. _F₂_, 1-6, the types found in the second generation]
The characters described above are not of any great economic
importance. Biffen has shown that such important characters as
baking strength and resistance to the disease known as yellow rust
behave on crossing in the same way as beard. Working on the lines of
the experiment described above he has succeeded in producing several
new varieties which in baking strength and in rust resistance are a
distinct advance on any varieties in cultivation in this country.
His method of working was to collect wheats from every part of the
world, to sow them and to pick out from the crop, which was usually
a mixed one, all the pure types he could. These were grown on small
plots for several years under close observation. Many were found to
be worthless and were soon discarded. Others were observed to possess
some one valuable character. Amongst these a pure strain of Red Fife
was obtained from Canadian seed, which was found to retain when grown
in England the excellent baking strength of the hard wheats of Canada
and North America. Again, other varieties were noticed to remain free
from yellow rust year after year, even when varieties on adjoining
plots were so badly infected that they failed to produce seed. Other
varieties, too, were preserved for the sturdiness of their straw,
their earliness in ripening, vigour of growth, or yielding capacity.
Many crosses were made with these as parents. The illustration shows
a corner of the Cambridge wheat-breeding enclosure including a
miscellaneous collection of parent varieties. The paper bags on the
ears show where crosses have been made. From the second generation
numbers of individual plants possessing desirable characters were
picked out, and the fixed types isolated in the third generation by
making cultures from the seed of these single plants. The seed from
these fixed types was sown on small field plots, at which stage many
had to be rejected because they were found wanting in some character
of great practical importance which did not make itself evident in
the breeding enclosure. The illustration shows a case in point. It
was photographed after heavy rain in July. The weakness of the straw
of the variety on the left had not been noticed in the enclosure. The
types which approved themselves on the small field plots were again
grown on larger plots so that their yield and milling and baking
characters could be tested. So far two types have survived the ordeal.
One combines the cropping power of the best English varieties with the
baking strength of North American hard wheat. It is the outcome of a
cross between Rough Chaff and Red Fife. Its average crop in 1911 was 38
bushels per acre as the result of 28 independent trials, and, where the
local millers have found out its quality, it makes on the market four
or five shillings per quarter more than the ordinary English varieties.
The other resulted from a cross between Square Head’s Master and
a rust-resisting type isolated from a graded Russian wheat called
Ghirka. It is practically rust-proof. Consequently it yields a heavier
crop than any of the ordinary varieties which are all more or less
susceptible to rust. The presence of rust in and on the leaves hinders
the growth of the plant, lowers the yield, and increases the proportion
of shrivelled grains. It has been estimated that rust diminishes the
world’s wheat crop by something like one third. The new rust-proof
variety gave an average yield of about 6 bushels per acre more than
ordinary varieties on the average of 28 trials last year. It is called
Little Joss and is especially valuable in the Fens and other districts
where rust is more than usually virulent.
[Illustration: Fig. 5. Corner of bird-proof enclosure showing a varied
assortment of parent varieties of wheat. Crosses have been made on some
of them as shown by the ears tied up in paper bags]
[Illustration:
Fig. 6. Field plots of two new varieties of the same parentage
which had approved themselves in the bird-proof enclosure. That
on the left had to be rejected on account of the weakness of
its straw. That on the right is the rust-proof variety known as
Little Joss. The photograph was taken after a storm which in
the open field found out the weak point of the one variety]
CHAPTER IV
THE QUALITY OF WHEAT FROM THE MILLER’S POINT OF VIEW
To the miller the quality of wheat depends on three chief factors, the
percentage of dirt, weed seeds, and other impurities, the percentage of
water in the sample, and a complex and somewhat ill-defined character
commonly called strength.
With the methods of growing, cleaning and thrashing wheat practised in
Great Britain, practically clean samples are produced, and home grown
wheat is therefore on the whole fairly free from impurities. This is,
however, far from the case with foreign wheats, many of which arrive at
the English ports in an extremely dirty condition. They are purchased
by millers subject to a deduction from the price for impurities above
the standard percentage which is allowed. The purchase is usually made
before the cargo is unloaded. Official samples are taken during the
unloading in which the percentage of impurities is determined, and the
deduction, if any, estimated.
The percentage of water, the natural moisture as it is usually called,
varies greatly in the wheats of different countries. In home grown
wheats it is usually 16 per cent., but in very dry seasons it may be
much lower, and in wet seasons it may rise to 18 per cent. Foreign
wheats are usually considerably drier than home grown wheats. In
Russian wheats 12 per cent. is about the average, and that too is about
the figure for many of the wheats from Canada, the States, Argentina,
and parts of Australia. Indian wheats sometimes contain less than 10
per cent. This is also about the percentage in the wheats of the arid
lands on the Pacific coast and in Australia. These figures show that
home grown wheats often contain as much as 5 per cent. more water
than the foreign wheats imported from the more arid countries. The
more water a wheat contains the less flour it will yield in the mill.
Consequently the less its value to the miller. A difference of 5 per
cent. of natural moisture means a difference in price of from 1_s._
6_d._ to 2_s._ per quarter in favour of the drier foreign wheats. This
is one of the reasons why foreign wheats command a higher price than
those grown in this country.
Turning to the third factor which determines the quality of wheat from
the miller’s point of view, we may for the present define strength
as the capacity for making bread which suits the public taste of the
present day. We shall discuss this point more fully when we deal with
the baking of bread. At present the only generally accepted method of
determining the strength of a sample of wheat is to mill it and bake
it, usually into cottage loaves. The strength of the wheat is then
determined from their size, shape, texture, and general appearance. A
really strong flour makes a large, well risen loaf of uniformly porous
texture. Wheats lacking in strength are known as weak. A weak wheat
makes a small flat loaf. In order to give a numerical expression to
the varying degrees of strength met with in different wheats, the Home
Grown Wheat Committee of the National Association of British and Irish
Millers have adopted a scale as the result of many thousand milling
and baking tests. On their scale the strength of the best wheat
imported from Canada, graded as No. 1 Manitoban, or from the States
graded as No. 1 Hard Spring, is taken as 100, that of the well-known
grade of flour known as London Households as 80, and that of the
ordinary varieties of home grown wheat, such as Square Head’s Master,
Browick, Stand Up, etc., as 65. The strength of most foreign wheats
falls within these limits. Thus the strength of Ghirka wheat from
Russia is about 85, of Choice White Karachi from India 75, of Plate
River wheat from the Argentine 80, etc. The strongest of all wheats is
grown in certain districts in Hungary. It is marked above 100 on the
scale, but it is not used for bread making. The soft wheats from the
more arid regions in Australia and the States are usually weaker than
average home grown samples, and are marked at 60. Rivet or cone wheat,
a heavy cropping bearded variety much grown by small holders,--since
the sparrow, which would ruin small plots of any other variety, seems
to dislike Rivet, possibly on account of its beard,--is the weakest of
all wheats, and is only marked at 20, which means that bread baked
from Rivet flour alone would be practically unsaleable. Rivet wheat
finds a ready sale, however, for making certain kinds of biscuits.
[Illustration: Fig. 7. Loaves made from No. 1 Manitoba. Strength 100]
[Illustration: Fig. 8. Loaves made from average English wheat. Strength
65]
[Illustration: Fig. 9. Loaves made from Rivet wheat. Strength 20]
In order to make flour which will bake bread to suit the taste of the
general public of the present day, the miller finds it necessary to
include in the mixture or blend of wheats which he grinds a certain
proportion of strong wheats such as Canadian, American, or Russian.
The quantity of strong wheat available is limited. Consequently strong
wheat commands a relatively high price. The average difference in price
of say No. 1 Manitoban and home grown wheat is about 5_s._ per quarter.
It is possible of course that the public taste in bread may change,
and damp close textured bread may become fashionable. In this case no
doubt the difference in price would disappear. Under present conditions
the necessity of including in his grinding mixture a considerable
proportion of strong foreign wheat is a distinct handicap against the
inland miller as compared with the port miller. The latter gets his
foreign wheat direct from the ship in which it is imported, whilst
the former has to pay railway carriage from the port to his mill. The
question naturally arises--is it not possible to grow strong wheats at
home and sell them to the inland miller?
This question has been definitely answered by the work of the Home
Grown Wheat Committee during the last 12 years. The committee
collected strong wheats from every country where they are produced,
and grew them in England. From the first crop they picked out single
plants of every type represented in the mixed produce, for strong
wheats as imported are usually grades and not pure varieties. From the
single plants they have established pure strains of which they have
grown enough to mill and bake. From most of the strong wheats they
were unable to find any strain which would produce strong wheat in
England. Thus the strong wheat of Hungary when grown in England was
no stronger than any of the ordinary typical home grown wheats. But
from the strong wheat of Canada was isolated the variety known as Red
Fife, which makes up a very large proportion of the higher grades of
American and Canadian wheats, and this variety when grown in England
was found to continue to produce wheat as strong as the best Canadian.
Year after year it has been grown here, and when milled and baked its
strength has been found to be 100 or thereabouts on the scale above
described. Finally it was found that a strain of Red Fife which had
been brought over from Canada 20 years ago, and grown continuously in
the western counties ever since, under the name of Cook’s Wonder, was
still producing wheat which when ground and baked possessed a strength
of about 100. Thus it was conclusively proved that in the case of
Red Fife at any rate the English climate was capable of producing
really strong wheat. The strength of Hungarian and Russian wheats
appear to be dependent on the climate of those countries. Red Fife,
however, produces strong wheat wherever it is grown. It is interesting
to note that this variety although first exploited in Canada and the
States is really of European origin. It was taken out to Canada by an
enterprising Scotchman called Fife in a mixed sample of Dantzig wheat.
He grew it for some time and distributed the seed. Pure strains have
from time to time been selected by the American and Canadian experiment
stations.
But the discovery that Red Fife would produce strong wheat in England
by no means solved the problem, for when the Home Grown Wheat Committee
distributed seed of their pure strain of that variety for extended
testing throughout the country, it was soon found to be only a poor
yielder except in a few districts. A yield of three quarters of strong
grain, even if it makes 40_s._ per quarter on the market, only gives to
the farmer a return of £6 per acre, as compared with a return of nearly
£8 from 4½ quarters of weak grain worth 35_s._ per quarter, which can
usually be obtained by growing Square Head’s Master, or some other
standard variety.
[Illustration:
Fig. 10. The left-hand loaf was made from average English
wheat. The loaf in the centre was made from Burgoyne’s Fife,
and is practically identical in size and shape with the
right-hand loaf which was made from imported No. 1 Manitoba]
It was at this point that Mendel’s discoveries came to the rescue.
Working on the Mendelian lines already explained, Biffen at Cambridge
crossed Red Fife with many of the best English varieties. From one of
the crosses he was able to isolate a new variety in which are combined
the strength of Red Fife and the vigour and cropping power of the
English parent. This variety, known as Burgoyne’s Fife, has been grown
and distributed by members of the Millers’ Association. In 1911 on the
average of 28 separate trials it yielded 38 bushels per acre, which
is well above the average of the best English varieties. It has been
repeatedly milled and baked, and its strength is between 90 and 100,
practically the same as that of Red Fife. It has been awarded many
prizes at agricultural shows for quality, and it commands on markets
where the local millers have found out its baking qualities about the
same price as the best foreign strong wheats, that is to say from
4_s._ to 5_s._ per quarter more than the average price of home grown
wheat. Taking a fair average yield of wheat as four quarters per acre,
Burgoyne’s Fife gives to the farmer an increased return over the
ordinary varieties of about 16_s._ per acre. The introduction of such a
variety makes the production of strong wheat in England a practicable
reality, and will be a boon both to the farmer and to the inland
miller. It is likely too that the possibility of obtaining a better
return per acre will induce farmers to grow more wheat. Anything that
tends to increase the production of home grown wheat and makes Great
Britain less dependent on foreign supplies is a national asset of the
greatest value.
It is of the greatest importance to the miller that he should be able
to determine the strength of the wheats he buys. Obviously the method
mentioned above, which entails milling enough of the sample to enable
him to bake a batch of bread, is far too lengthy to be of use in
assessing the value of a sample with a view to purchase. The common
practice is for the miller or corn merchant to buy on the reputation
of the various grades of wheat, which he confirms by inspection of
the sample. Strength is usually associated with certain external
characters which can readily be judged by the eye of the practised
wheat buyer. Strong wheats are usually red in colour, their skin is
thin and brittle, the grain is usually rather small, and has a very
characteristic horny almost translucent appearance. The grains are
extremely hard and brittle, and when broken the inside looks flinty.
On chewing a few grains the starch is removed and there remains in the
mouth a small pellet of gluten, which is tough and elastic like rubber,
but not sticky.
Weak wheats as a rule possess none of these characters. Their colour
may be either red or white, their skin is commonly thick and tough,
the grain is usually large and plump, and often has an opaque mealy
appearance. It is soft and breaks easily, and the inside is white, soft
and mealy. Very little gluten can be separated from it by chewing, and
that little is much less tough and elastic than the gluten of a strong
wheat.
These characters, however, are on the whole less reliable than the
reputation of the grade of wheat under consideration. To make a
reliable estimate of strength from inspection of a sample of wheat
requires a natural gift cultivated by continual practice. Even the
best commercial judges of wheat have been known to be deceived by
a sample of white wheat which subsequent milling and baking tests
showed to possess the highest strength. The mistake was no doubt due
to the great rarity of strength among white wheats. This rarity will
doubtless soon disappear now that a pure strain of White Fife has
been isolated and shown to possess strength quite equal to that of Red
Fife. Sometimes too the ordinary home grown varieties produce most
deceptive samples which show all the external characters of strong
wheats. Such samples, however, on milling and baking are invariably
found to possess the usual strength of home grown wheat, about 65 on
the scale. These considerations show the great need of a scientific
method of measuring strength, which can be carried out rapidly and on a
small sample of grain. This need is felt at the present time not only
by the miller and the merchant, but by the wheat breeder. For instance,
in picking out the plants possessing strong grain from cultures of the
second generation after making his crosses, the plant breeder up to the
present has had to rely on inspection by eye, and on the separation of
gluten by chewing, for a single plant obviously cannot yield enough
grain to mill and bake. This fact no doubt explains the differences of
opinion among plant breeders on the inheritance of strength, for it is
not every one who can acquire the power of judging wheat accurately by
his senses. Such a faculty is a personal gift, and is at best apt to
fail at times.
The search for a rapid and accurate method of measuring strength has
for many years attracted the attention of investigators. As might be
expected most of the investigations have centred round the gluten,
for as mentioned above the gluten of a strong wheat is much more tough
and elastic than that of a weak wheat. Gluten is a characteristic
constituent of all wheats, and it is the presence of gluten which
gives to wheat flour the power of making bread. The other cereals,
barley, oats, maize and rice are very similar to wheat in their general
chemical composition, but they do not contain gluten. Consequently they
cannot make bread.
In making bread flour is mixed with water and yeast. The yeast feeds
on the small quantity of sugar contained in the flour, fermenting
it and forming from it alcohol and carbon dioxide gas. The gluten
being coherent and tough is blown into numberless small bubbles by
the gas, which is thus retained inside the bread. On baking, the high
temperature of the oven fixes these bubbles by drying and hardening
their walls, and the bread is thus endowed with its characteristic
porous structure. If a cereal meal devoid of gluten is mixed with water
and yeast, fermentation will take place with formation of gas, but the
gas will escape at once, and the product will be solid and not porous.
Evidently from the baking point of view gluten is of the greatest
importance. One of the most obvious methods that have been suggested
for estimating the strength of wheat depends on the estimation of the
percentage of gluten contained in the flour. The method has not turned
out very successfully, for strength seems to depend rather on the
quality than on the quantity of gluten in the wheat. Much attention has
been given to the study of the causes of the varying quality of the
gluten of different wheats. Gluten for instance has been shown to be
a mixture of two substances, gliadin and glutenin, and the suggestion
has been made that its varying properties are dependent on the varying
proportions of these two substances present in different samples. This
suggestion however failed to solve the problem.
After seven years of investigation the author has worked out the
following theory of the strength of wheat flours, which has finally
enabled him to devise a method which promises to be both accurate and
rapid, and to require so little flour that it can readily be used by
the wheat breeder to determine the strength of the grain in a single
ear. It has already been mentioned that a strong wheat is one that will
make a large loaf of good shape and texture. The strength of a wheat
may therefore be defined as the power of making a large loaf of good
shape and texture. Evidently strength is a complex of at least two
factors, size and shape, which are likely to be quite independent of
each other. Not infrequently, for instance, wheats are met with which
make large loaves of bad shape, or on the other hand, small loaves
of good shape. Probably therefore the size of the loaf depends on one
factor, the shape on another; and the failure of the many attempts
to devise a method of estimating strength have been caused by the
impossibility of measuring the product of two independent factors by
one measurement.
It seemed a feasible idea that the size of the loaf might depend on
the volume of gas formed when yeast was mixed with different flours.
On mixing different flours with water and yeast it was found that for
the first two or three hours they all gave off gas at about the same
rate. The reason of this is that all flours contain about the same
amount of sugar, approximately one per cent., so that at the beginning
of the bread fermentation all flours provide the yeast with about the
same amount of sugar for food. But this small amount of sugar is soon
exhausted, and for its subsequent growth the yeast is dependent on the
transformation of some of the starch of the flour into sugar. Wheat
like many other seeds contains a ferment or enzyme called diastase,
which has the power of changing starch into sugar, and the activity of
this ferment varies greatly in different wheats. The more active the
ferment in a flour the more rapid the formation of sugar. Consequently
the more rapidly the yeast will grow, and the greater will be the
volume of gas produced in the later stages of fermentation in the
dough. As a rule it is not practicable to get the dough moulded into
loaves and put into the oven before it has been fermenting for about
six or eight hours. If the flour possesses an active ferment it will
still be rapidly forming gas at the end of this time, and the loaf will
go into the oven distended with gas under pressure from the elasticity
of the gluten which forms the walls of the bubbles. The heat of the
oven will cause each gas bubble to expand, and a large loaf will be the
result. If the ferment of the flour is of low activity it will not be
able to keep the yeast supplied with all the sugar it needs, the volume
of gas formed in the later stages of the fermentation of the dough will
be small, the dough will go into the oven without any pressure of gas
inside it, little expansion will take place as the temperature rises,
and a small loaf will be produced.
From these facts it is quite easy to devise a method of estimating how
large a loaf any given flour will produce. The following method is that
used by the author. A small quantity of the flour, usually 20 grams,
is weighed out and put into a wide mouthed bottle. A flask of water
is warmed to 40° C., of this 100 c.c. is measured out, and into it 2½
grams of compressed yeast is intimately mixed, 20 c.c. of the mixture
being added to the 20 grams of flour in the bottle. The flour and
yeast-water are then mixed into a cream by stirring with a glass rod.
The bottle is then placed in a vessel of water which is kept by a small
flame at 35° C. The bottle is connected to an apparatus for measuring
gas, and the volume of gas given off every hour is recorded. As already
mentioned all flours give off about the same volume of gas during the
first three hours. After this length of time the volume of gas given
off per hour varies greatly with different flours. Thus a flour which
will bake a large loaf gives off under the conditions above described
about 20 c.c. of gas during the sixth hour of fermentation, whilst a
flour which bakes a small tight loaf gives off during the sixth hour of
fermentation only about 5 c.c. of gas.
Having devised a feasible method of estimating how large a loaf any
given flour will make, the problem of the shape and texture still
remains. Previous investigators had exhausted almost every possible
chemical property of gluten in their search for a method of estimating
strength. The author therefore determined to study its physical
properties. Now gluten is what is known as a colloid substance, like
albumen the chief constituent of white of egg, casein the substance
which separates when milk is curdled, or clay which is a well known
constituent of heavy soils. Such colloid substances can scarcely be
said to possess definite physical properties of their own, for their
properties vary so largely with their surroundings. The white of a
fresh egg is a thick glairy liquid. On heating it becomes a white
opaque solid, and the addition of certain acids produces a similar
change in its properties. Casein exists in fresh milk in solution. The
addition of a few drops of acid causes it to separate as finely divided
curd. If, however, the milk is warmed before the acid is added the
casein separates as a sticky coherent mass. Every farmer knows that
lime improves the texture of soils containing much clay, because the
lime causes the clay to lose its sticky cohesive nature.
Such instances show that the properties of colloid substances are
profoundly modified by the presence of chemical substances. Wheat,
like almost all plant substances, is slightly acid, and the degree of
acidity varies in different samples. Accordingly the effect of acids on
the physical properties of gluten was investigated, and it was found
that by placing bits of gluten in pure water and in acid of varying
concentration it could be made to assume any consistency from a state
of division so fine that the separate particles could not be seen,
except by noticing that their presence made the water milky, to a tough
coherent mass almost like indiarubber (Fig. 11). It was found, however,
that the concentration of acid in the wheat grain was never great
enough to make the gluten really coherent.
[Illustration: Fig. 11.
Gluten in pure water; soft, but tough and elastic
Gluten in very weak hydrochloric acid (3 parts in 100,000 of water); it
floats about in powder, having entirely lost cohesion, and makes the
water milky
Gluten in hydrochloric acid (3 parts in 1000 of water); very hard and
tough]
But wheat contains also varying proportions of such salts as chlorides,
sulphates and phosphates, which are soluble in water, and the action
of such salts on gluten was next tried. It was at once found that
these salts in the same concentration as they exist in the wheat grain
were capable of making gluten coherent, but that the kind of coherence
produced was peculiar to each salt. Phosphates produce a tough and
elastic gluten such as is found in the strongest wheats. Chlorides and
sulphates on the other hand make gluten hard and brittle, like the
gluten of a very weak wheat (Fig. 12).
The next step was to make chemical analyses to find out the amount of
soluble salts in different wheats. Strong wheats of the Fife class
were found to contain not less than 1 part of soluble phosphate in
1000 parts of wheat, whilst Rivet wheat, the weakest wheat that comes
on the market, contained only half that amount. Rivet, however, was
found to be comparatively rich in soluble chlorides and sulphates,
which are present in very small amounts in strong wheats of the Fife
class. Ordinary English wheats resemble Rivet, but they contain rather
more phosphate and rather less chlorides and sulphates. After making a
great many analyses it was found that the amount of soluble phosphate
in a wheat was a very good index of the shape and texture of the loaf
which it would make. The toughness and elasticity of the gluten no
doubt depend on the concentration of the soluble phosphate in the wheat
grain, the more the soluble phosphate the tougher and more elastic
the gluten, and a tough and elastic gluten holds the loaf in shape as
it expands in the oven, and prevents the small bubbles of gas running
together into large holes and spoiling the texture.
[Illustration: Fig. 12.
Gluten in water containing both acid and phosphate; very tough and
elastic
Gluten in water containing both acid and sulphates. It shows varying
degrees of coherence, but is brittle or “short”]
These facts suggest at once a method for estimating the shape and
texture of the loaf which can be made from any given sample of wheat.
An analysis showing the amount of soluble phosphate in the sample
should give the desired information. But unfortunately such an analysis
is not an easy one to make, and requires a considerable quantity of
flour. In making these analyses it was noticed that when the flours
were shaken with water to dissolve the phosphate, and the insoluble
substance removed by filtering, the solutions obtained were always more
or less turbid, and the degree of turbidity was found to be related
to the amount of phosphate present and to the shape of loaf produced.
On further investigation it was found that the turbidity was due to
the fact that the concentration of acid and salts which make gluten
coherent, also dissolve some of it, and gluten like other colloids
gives a turbid solution. It was also found that the amount of gluten
dissolved, and consequently the degree of turbidity, is related to
the shape of the loaf which the flour will produce. Now it is quite
easy to measure the degree of turbidity of a solution by pouring the
solution into a glass vessel below which a small electric lamp is
placed, and noting the depth of the liquid through which the filament
of the lamp can just be seen. The turbidities were, however, so slight
that it was found necessary to increase them by adding a little iodine
solution which gives a brown milkiness with solutions of gluten, the
degree of milkiness depending on the amount of gluten in the solution.
In this way a method was devised which is rapid, easy, and can be
carried out with so little wheat that the produce of one ear is amply
sufficient. It can therefore be used by the plant breeder for picking
out from the progeny of his crosses those individual plants which are
likely to give shapely loaves. The method is as follows: An ear of
wheat is rubbed out and ground to powder in a small mill. One gram of
this powder, or of flour if that is to be tested, is weighed out and
put into a small bottle. To it is added 20 c.c. of water. The bottle
is then shaken for one hour. At the end of this time the contents are
poured onto a filter. To 15 c.c. of the solution 1½ c.c. of a weak
solution of iodine is added, and after standing for half an hour the
turbidity test is applied. Working in this way it is possible to see
through only 10 c.m. of the solution thus obtained from such a wheat as
Red Fife, as compared with 25 c.m. in the case of Rivet. Other wheats
yield solutions of intermediate opacity. This method is now being
tested in connection with the Cambridge wheat breeding experiments.
CHAPTER V
THE MILLING OF WHEAT
In order that wheat may be made into bread it is necessary that it
should be reduced to powder. In prehistoric times this was effected by
grinding the grain between stones. Two stones were commonly used, the
lower one being more or less hollowed on its upper surface so as to
hold the grain while it was rubbed by the upper one. As man became more
expert in providing for his wants, the lower stone was artificially
hollowed, and the upper one shaped to fit it, until in process of time
the two stones assumed the form of a primitive mortar and pestle.
The next step in the evolution of the mill was to make a hole or groove
in the side of the lower stone through which the powdered wheat could
pass as it was ground. This device avoided the trouble of emptying the
primitive mill, and materially saved the labour of the grinder. Such
mills are still in use in the less civilised countries in the East, and
are of course worked by hand as in primitive times.
They gradually developed as civilization progressed into the stone
mills which ground all the breadstuffs of the civilised world until
about 40 years ago. The old fashioned stone mill was, and indeed still
is, a weapon of the greatest precision. It consists of a pair of stones
about four feet in diameter, the lower of which is fixed whilst the
upper is made to revolve by mechanical power at a high speed. Each
stone is made of a large number of pieces of a special kind of hard
stone obtained from France. These pieces are cemented together, and
the surfaces which come into contact are patiently chipped until they
fit one another to a nicety all over. The surface of the lower stone
is then grooved so as to lead the flour to escape from between the
stones at definite places where it is received for further treatment.
The grain to be ground is fed between the stones through a hole at the
centre of the upper stone. It has been stated above that the surfaces
of the two stones are in contact. As a matter of fact this is not
strictly true. The upper stone is suspended so that the surfaces are
separated by a small fraction of an inch, and it will be realised
at once that this suspension is a matter of the greatest delicacy.
To balance a stone weighing over half a ton so that, when revolving
at a high rate of speed, it may be separated from its partner at no
point over its entire surface of about 12 square feet by more than
the thickness of the skin of a grain of wheat, and yet may nowhere
come into actual contact, is an achievement of no mean order. Stone
mills of this kind were usually driven by water power, or in flat
neighbourhoods by wind power, though in some cases steam was used.
It was the common practice to subject the ground wheat from the stones
to a process of sifting so as to remove the particles of husk from
the flour. The sifting was effected by shaking the ground wheat in a
series of sieves of finely woven silk, known as bolting cloth. In this
way it was possible to obtain a flour which would make a white bread.
The particles of husk removed by the sifting were sold to farmers for
food for their animals, under the name of bran, sharps, pollards, or
middlings, local names for products of varying degrees of fineness,
which may be classed together under the general term wheat offals. The
ideal of the miller was to set his stones so that they would grind
the flour to a fine powder without breaking up the husk more than was
absolutely necessary. When working satisfactorily a pair of stones were
supposed to strip off the husk from the kernel. The kernel should then
be finely pulverised. The husk should be flattened out between the
stones, which should rub off from the inside as completely as possible
all adhering particles of kernel. If this ideal were attained, the
mill would yield a large proportion of fairly white flour, and a small
proportion of husk or offals.
As long as home grown wheats were used this ideal could be more or
less attained because the husk of these wheats is tough and the kernel
soft. Comparatively little grinding suffices to reduce the kernel to
the requisite degree of fineness, and this the tough husk will stand
without being itself unduly pulverised. Consequently the husk remains
in fairly large pieces, and can be separated by sifting, with the
result that a white flour can be produced. But home grown wheat ceased
to provide for the wants of the nation more than half a century ago.
Already in 1870 half the wheat ground into flour in the United Kingdom
was imported from abroad, and this proportion has steadily increased,
until at the present time only about one-fifth of the wheat required is
grown at home. Many of the wheats which are imported are harder in the
kernel, and thinner and more brittle in the husk, than the home grown
varieties. Consequently they require more grinding to reduce the kernel
to the requisite degree of fineness, and their thin brittle husk is
not able to resist such treatment. It is itself ground to powder along
with the kernel, and cannot be completely separated from the flour
by sifting. Such wheats therefore, when ground between stones, yield
flour which contains much finely divided husk, and this lowers its
digestibility and gives it a dark colour.
In the decades before 1870 when the imports of foreign wheats first
reached serious proportions, and all milling was done by stones, dark
coloured flours were common, and people would no doubt have accepted
them without protest, if no other flours had been available. But as it
happened millers in Hungary, where hard kernelled, thin skinned wheats
had long been commonly grown, devised the roller milling process, which
produces fine white flour from such wheats, no matter how hard their
kernels or how thin their skins. The idea of grinding wheat between
rollers was at once taken up in America and found to give excellent
results with the hard thin skinned wheats of the north-west. The fine
white flours thus produced were sent to England, and at once ousted
from the home markets the dark coloured flours produced from imported
wheats in the English stone mills. The demand for the white well-risen
bread produced from these roller milled imported flours showed at once
that the public preferred such bread to the darker coloured heavier
bread yielded by stone-ground flours, especially those made from the
thin skinned foreign wheats.
This state of things was serious both for the millers and the farmers.
The importation of flour instead of wheat must obviously ruin the
milling industry, and since wheat offals form no inconsiderable item
in the list of feeding stuffs available for stock keepers, a decline
of the milling industry restricts the supply of food for his stock,
and thus indirectly affects the farmer. At the same time the preference
shown by the public for bread made from fine white imported flour, to
some extent depreciated the value of home grown wheat.
It was by economic conditions of this kind that the millers were
compelled in the early seventies to alter their methods. The large
firms subscribed more capital and installed roller plant in their
mills. These at once proved a success and the other firms have followed
suit. At the present time considerably more than 90 per cent. of the
flour used in this country is the product of roller mills. The keen
competition which has arisen in the milling industry during the last 35
years has produced great improvements in roller plant, and the methods
of separation now in use yield flours which in the opinion of the
miller, and apparently too in the opinion of the general public, are
far in advance of the flours which were produced in the days of stone
milling.
Perhaps the first impression which a visitor to a modern roller mill
would receive is the great extent to which mechanical contrivances have
replaced hand labour. Once the wheat has been delivered at the mill
it is not moved again by hand until it goes away as flour and offals.
It is carried along by rapidly moving belts, elevated by endless
chains carrying buckets, allowed to fall again by gravity, or perhaps
in other cases transported by air currents. Another very striking
development is the great care expended in cleaning the grain before
it is ground. This cleaning is the first process to which the wheat
is subjected. It is especially necessary in the case of some of the
foreign wheats which arrive in this country in a very dirty condition.
The impurities consist of earth, weed seeds, bits of husk and straw;
iron nails, and other equally unlikely objects are by no means
uncommon. Some of these are removed by screens, but besides screening
the wheat is actually subjected to the process of washing with water.
For this purpose it is elevated to an upper floor of the mill, and
allowed to fall downwards through a tall vessel through which a stream
of water is made to flow. As it passes through the water it is scrubbed
by a series of mechanically driven brushes to remove the earthy matter
which adheres to the grain. This is carried away by the stream of water.
After cleaning the grain next undergoes the process of conditioning.
The object of this process is so to adjust the moisture of the grain
that the husk may attain its maximum toughness compatible with a
reasonable degree of brittleness of kernel, the idea being to powder
the kernel with the minimum of grinding and without unduly powdering
the husk. By attention to this process separation of flour and husk
is made easier and more complete. The essential points in the process
are to moisten the grain, either in the course of cleaning as above
described, or if washing is not necessary, by direct addition of water.
The moisture is given some time to be absorbed into the grain, which is
then dried until the moisture content falls to what experience shows to
be the most successful figure for the wheat in question.
[Illustration: Fig. 13. First break rolls seen from one end. The ribs
can just be seen where the two rolls touch]
Cleaning and conditioning having been attended to, the grain is now
conveyed to the mill proper. This of course is done by a mechanical
arrangement which feeds the grain at any desired rate into the hopper
which supplies the first pair of rolls. These rolls consist of a pair
of steel cylinders usually 10 inches in diameter and varying in length
from 20 inches to 5 feet according to the capacity of the mill. The
surfaces of the cylinders are fluted or ribbed, the distance from
rib to rib being about one-tenth of an inch. The rollers are mounted
so that the distance between their surfaces can be adjusted. They
are set so that they will break grains passing between them to from
one-half to one-quarter their original size. They are made to revolve
so that the parts of the surfaces between which the grains are nipped
are travelling in the same direction. One roll revolves usually at
about 350 revolutions per minute, the other at rather less than half
that rate (Fig. 14). It is obvious from the above description that a
grain of wheat falling from the hopper on to the surface of the moving
rollers will be crushed or nipped between them, and that since the
rollers are moving at different rates, it will at the same time be more
or less torn apart. By altering the distance between the rollers and
their respective speeds of revolution the relative amounts of nipping
and tearing can be adjusted to suit varying conditions.
[Illustration:
Fig. 14. Break rolls. The large and small cog-wheels are the
simplest device used to give the two rolls different speeds.
The larger cog-wheel is driven by power and drives the smaller,
of course at a much higher rate of revolution]
The passage of the grain through such a pair of rollers is known
technically as a break. Its object is to break or tear open the grain
with the least possible amount of friction between the grain and the
grinding surfaces. Since the rollers are cylindrical it is obvious that
the grain will only be nipped at one point of their surfaces, and even
here the friction is reduced as much as possible by making both the
grinding surfaces move in the same direction. As already explained it
can be diminished, if the condition of the wheat allows, by diminishing
the difference in speed between the two rolls. The result of the first
break is to tear open the grains. At the same time a small amount of
the kernel will be finely powdered. The rest of the kernel and husk
will still remain in comparatively large pieces. The tearing open of
the grain sets free the dirt which was lodged in the crack or furrow
which extends from end to end of the grain. This dirt cannot be removed
by any method of cleaning. It only escapes when the grain is torn
open in the break. It is generally finely divided dirt and cannot be
separated from the flour formed in this process. Consequently the
first break flour is often more or less dirty, and the miller tries to
adjust his first break rolls so that they will form as little flour as
possible. The first break rolls not only powder a little of the kernel,
but they also reduce to a more or less fine state of division a little
of the husk.
The result of the passage of the grain through the first break rolls
is to produce from it a mixture of a large quantity of comparatively
coarse particles of kernel to many of which husk is still adherent,
a small quantity of finely divided flour which is more or less
discoloured with dirt, and a small quantity of finely divided husk.
This mixture, which is technically known as stock, is at once subjected
to what is called separation, with the object of separating the flour
from the other constituents before it undergoes any further grinding.
It is one of the guiding principles of modern milling that the flour
produced at each operation should be separated at once so as to reduce
to a minimum the grinding which it has to undergo. Separation is
brought about by the combination of two methods. The stock is shaken
in contact with a screen made of bolting silk so finely woven that it
contains from 50 to 150 meshes to the inch, according to the fineness
of the flour which it is desired to separate. The shaking is effected
in several different ways. Sometimes the silk is stretched on a frame
so as to make a kind of flat sieve. This is shaken mechanically whilst
the stock is allowed to trickle over its surface, so that the finely
divided particles of flour may fall through the meshes and be collected
separately from the larger particles which remain on the top. These
larger particles are partly heavy bits of broken kernel and partly
light bits of torn husk. In order to separate them advantage is taken
of the fact that a current of wind can be so adjusted that it will blow
away the light and fluffy husk particles without disturbing the heavy
bits of kernel. By means of a mechanically driven fan a current of
air is blown over the surface of the sieve, in the direction opposite
to that in which the stock is travelling. As the stock rolls over and
over in its passage from the upper to the lower end of the inclined
sieve the fluffy particles of husk are picked up by the air current
and carried back to the top of the sieve where they fall, as the
current slackens, into a receptacle placed to receive them. Thus by
the combination of sifting and air carriage the stock is separated
into a small quantity of finished flour, a small quantity of finished
husk or offal, and a large quantity of large particles of kernel with
husk still adhering to some of them. These large particles, which
are called semolina, of course require further grinding. Different
methods of sifting are often used in place of the one above described,
especially for completing the purification of the flour. Sometimes the
silk is stretched round a more or less circular frame so as to form
a long cylinder covered with silk. The stock is delivered into the
higher end of this cylinder which is made to revolve. This causes the
stock to work its way through the cylinder, and during its progress the
finely ground flour finds its way through the meshes, and is separated
as before from the coarser particles. Such a revolving sieve is known
as a reel. In a somewhat similar arrangement known as a centrifugal
a series of beaters is made to revolve rapidly inside a stationary
cylindrical sieve. The stock is admitted at one end and is thrown by
the revolving beaters against the silk cover. The finer particles are
driven through the meshes of the silk, the coarser particles find their
way out of the cylinder at the other end. Sometimes for separating
very coarse particles wire sieves of 30 meshes, or thereabouts, to the
inch are used. Whatever the method the object is to separate at once
the finished flour and offal from the large particles of kernel which
require further grinding.
[Illustration:
Fig. 15. A pair of reduction rolls. They are smooth, and the
cog-wheels being nearly of the same size the speed of the two
rolls is nearly equal]
These large particles, semolina, are next passed between one or more
pairs of smooth rolls known as reduction rolls (Fig. 15). These are
set rather nearer together than the break rolls, and the difference
in speed between each roll and its partner is quite small. The object
of reduction is to reduce the size of the large particles of semolina
and to produce thereby finely divided flour. The stock from the first
pair or pairs of reduction rolls contains much finely ground flour
mixed with coarser particles of kernel with or without adherent husk.
It is at once submitted to the separation and purification processes
as above described. This yields a large quantity of finished flour
which is very white and free from husk. It represents commercially
the highest grade of flour separated in the mill and is described
technically as patents. A small amount of finished offal is also
separated at this stage.
The coarse particles of kernel with adherent husk from which the flour
and offal have been separated are now passed through a second pair of
break rolls more finely fluted than before, known as the second break.
These are set closer together than the first break rolls. Their object
is to rub off more kernel from the husk. The stock from them is again
separated, the flour and finished offal being removed as before. The
coarser particles are again reduced by smooth reduction rolls, and a
second large quantity of flour separated. This is commercially high
grade flour and is usually mixed with the patents already separated.
The coarse particles left after this separation are usually subjected
to a third and a fourth break, each of which is succeeded by one or
two reductions. Separation of the stock and purification of the flour
take place after each rolling, so that as soon as any flour or husk is
finely ground it may be at once separated without further grinding.
The last pair of fluted rolls, the fourth break, are set so closely
together that they practically touch both sides of the pieces of
husk which pass through them. They are intended to scrape the last
particles of kernel from the husk. This is very severe treatment, and
usually results in the production of much finely powdered husk which
goes through the sifting silk and cannot be separated from the flour.
The flour from the fourth break is therefore usually discoloured by the
presence of much finely divided husk. For this reason it ranks as of
low commercial grade. The later reductions too yield flours containing
more or less husk, which darkens their colour. They are usually mixed
together and sold as seconds.
The fate of the germ in the process of roller milling is a point of
considerable interest, both on account of the ingenious way in which
it is removed, and because of the mysterious nutritive properties
which it is commonly assumed to possess. The germ of a grain of wheat
forms only about 1½ per cent. by weight of the grain. It differs in
composition from the rest of the grain, being far richer in protein,
fat, and phosphorus. Its special feeding value can, however, scarcely
be explained in terms of these ingredients, for its total amount is so
small that its presence or absence in the flour can make only a very
slight difference in the percentages of these substances. But this
point will be discussed fully in a subsequent chapter. Here it is the
presence of the fat which is chiefly of interest. According to the
millers the fat of the germ is prone to become rancid, and to impart
to the flour, on keeping, a peculiar taste and odour which affects its
commercial value. They have therefore devised with great ingenuity a
simple method of removing it. This method depends on the fact that the
presence in the germ of so much fat prevents it from being ground to
powder in its passage between the rolls. Instead of being ground it
is pressed out into little flat discs which are far too large to pass
with the flour through the sifting silks or wires, and far too heavy to
be blown away by the air currents which remove the offals. The amount
which is thus separated is usually about 1 per cent. of the grain so
that one third of the total quantity of germ present in the grain is
not removed as such. Considerable difficulties arise in attempting to
trace this fraction, and at present it is impossible to state with
certainty what becomes of it. The germ which is separated is sold by
the ordinary miller to certain firms which manufacture what are known
as germ flours. It is subjected to a process of cooking which is said
to prevent it from going rancid, after which it is ground with wheat,
the product being patent germ flour.
CHAPTER VI
BAKING
In discussing the method of transforming flour into bread it will be
convenient to begin by describing in detail one general method. The
modifications used for obtaining bread of different kinds, and for
dealing with flours of different qualities will be shortly discussed
later when they can be more readily understood.
Bread may be defined as the product of cooking or baking a mixture of
flour, water, and salt, which is made porous by the addition of yeast.
It is understood to contain no other substances than these--flour,
salt, water and yeast.
In the ordinary process the first step is to weigh out the flour which
it is proposed to bake. This is then transferred to a vessel which in a
commercial bakery is usually a large wooden trough, in a private house
an earthenware bowl. The necessary amount of yeast is next weighed out
and mixed with water. Nowadays compressed or German yeast is almost
always used at the rate of 1 to 2 lbs. per sack or 280 lbs. of flour.
For smaller quantities of flour relatively more yeast is needed, for
instance 2 ozs. per stone. Formerly brewers’ yeast or barm was used,
but its use has practically ceased because it is difficult to obtain
of standard strength. Some people who profess to be connoisseurs of
bread still prefer it because as they say it gives a better flavour
to the bread. The water with which the yeast is mixed is warmed so as
to make the yeast more active. The flour is then heaped up at one end
of the vessel in which the mixing is to take place, and salt at the
rate of 2 to 5 lbs. per sack is thoroughly stirred into it. A hollow
is then made in the heap of flour into which the mixture of yeast and
water is poured. More warm water is added so that enough water in all
may be present to convert all, or nearly all, the flour into dough of
the required consistency. When dealing with a flour with which he is
familiar the baker knows by experience how much water he requires per
sack. In the case of an unaccustomed brand of flour he determines the
amount by a preliminary trial with a small quantity (Figs. 16 and 17).
Flour from the heap is then stirred into the water until the whole of
the flour is converted into a stiff paste or dough as it is called.
By this method a little dry flour will always separate the dough from
the sides of the vessel and this will prevent the dough from sticking
to the vessel and the hands. The dough is then thoroughly worked or
kneaded so as to ensure the intimate mixture of the ingredients. The
vessel is then covered to keep the dough warm. In private houses
this is ensured by placing the vessel near the fire. In bakeries the
room in which the mixing is conducted is usually kept at a suitable
temperature. The yeast cells which are thoroughly incorporated in the
dough, find themselves in possession of all they require to enable them
to grow. The presence of water keeps them moist, and dissolves from
the flour for their use sugar and salts: the dough is kept warm as
above explained. Under these conditions active fermentation takes place
with the formation of alcohol and carbon dioxide gas. The alcohol is
of no particular consequence in bread making, the small amount formed
is probably expelled from the bread during its stay in the oven. The
carbon dioxide, however, plays a most important part. Being a gas it
occupies a large volume, and its formation throughout the mass of the
dough causes the dough to increase greatly in volume. The dough is said
by the housewife to rise, by the professional baker to prove.
[Illustration:
Fig. 16. Apparatus arranged for a baking test. Four loaves
which have just been scaled and moulded are seen in an
incubator where they are left to rise or prove before being
transferred to the oven]
[Illustration:
Fig. 17. The loaves shown in the last figure have just been
baked and are ready to be taken out of the oven, the door of
which is open. Note the different shapes. That on the right
hand is obviously shown by the test to be made from a strong
flour, the other from a very weak flour]
The process of kneading causes the particles of gluten to absorb
water and to adhere to one another, so that the dough may be regarded
as being composed of innumerable bubbles each surrounded by a thin
film of gluten, in or between which lie the starch grains and other
constituents of the flour. Each yeast cell as above explained forms a
centre for the formation of carbon dioxide gas, which cannot escape
at once into the air, and must therefore form a little bubble of
gas inside the particular film of gluten which happens to surround
it. The expansion of the dough is due to the formation inside it of
thousands of these small bubbles. It is to the formation of these
bubbles too that the porous honey-combed structure of wheaten bread is
due. Also since the formation of the bubbles is due to the retention
of the carbon dioxide by the gluten films, such a porous structure is
impossible in bread made from the flour of grains which do not contain
gluten.
The rising of the dough is usually allowed to proceed for several
hours. The baker finds by experience how long a fermentation is
required to give the best results with the flours he commonly uses.
When the proper time has elapsed, the dough is removed from the trough
or pan in which it was mixed to a board or table, previously dusted
with dry flour to prevent the dough adhering to the board or to the
hands. It is then divided into portions of the proper weight to
make loaves of the desired size. This process is known technically
as scaling. Usually 2 lbs. 3 ozs. of dough is allowed for baking a 2
lb. loaf. Each piece of dough is now moulded into the proper shape if
it is desired to bake what is known as a cottage loaf, or placed in
a baking tin if the baker is satisfied with a tinned loaf. In either
case the dough is once more kept for some time at a sufficiently warm
temperature for the yeast to grow so that the dough may once more be
filled with bubbles of carbon dioxide gas. As soon as this second
rising or proving has proceeded far enough the loaves are transferred
to the oven. Here the intense heat causes the bubbles of gas inside
the dough to expand so that a sudden increase in the size of the loaf
takes place. At the same time the outside of the loaf is hardened and
converted into crust.
After remaining in the oven for the requisite time the bread is
withdrawn and allowed to cool as quickly as possible, after which it is
ready for use or sale.
The method of baking which has been described above is known as the
off-hand or straight dough method. It possesses the merit of rapidity
and simplicity, but it is said by experts that it does not yield the
best quality of bread from certain flours. Perhaps the commonest
variation is that known as the sponge and dough method, which is
carried out as follows. As before, the requisite amount of flour is
weighed out into the mixing trough, and a depression made in it for
the reception of the water and yeast. These are mixed together in the
proper proportions, enough being taken to make a thick cream with
about one quarter of the flour. This mixture is now poured into the
depression in the flour, and enough of the surrounding flour stirred
into it to make a thick cream or sponge as it is called. At the same
time a small quantity of salt is added to the mixture. The sponge is
allowed to ferment for some hours, being kept warm as in the former
method. As soon as the time allowed for the fermentation of the sponge
has elapsed, more water is added, so that the whole or nearly the whole
of the flour can be worked up into dough. This dough is immediately
scaled and moulded into loaves, which after being allowed to prove
or rise for some time are baked as before. This method is used for
flours which do not yield good bread when they are submitted to long
fermentation. In such cases the mellow flours, which will only stand a
very short fermentation, are first weighed out into the mixing trough,
and a depression made in the mass of flour into which a quantity of
strong flour which can be fermented safely for a long time is added. It
is this last addition which is mixed up into the sponge to undergo the
long preliminary fermentation. The rest of the flour is mixed in after
this first fermentation is over, so that it is only subjected to the
comparatively slight fermentation which goes on in the final process of
proving.
Many other modifications are commonly practised locally, their object
being for the most part to yield bread which suits the local taste.
It will suffice to mention one which has a special interest. In this
method the essentially interesting point is the preparation of what is
known as a ferment. For this purpose a quantity of potatoes is taken,
about a stone to the sack of flour. After peeling and cleaning they
are boiled and mashed up with water into a cream. To this a small
quantity of yeast is added and the mixture kept warm until fermentation
ceases, as shown by the cessation of the production of gas. During
this fermentation the yeast increases enormously, so that a very small
quantity of yeast suffices to make enough ferment for a sack of flour.
The flour is now measured out into the trough, and the ferment and some
additional water and salt added so that the whole can be worked up into
dough. Scaling, moulding, and baking are then conducted as before. This
method was in general use years ago when yeast was dear. It has fallen
somewhat into disuse in these days of cheap compressed yeast, in fact
the use of potatoes nowadays would make the process expensive.
In private houses and in the smaller local bakeries the whole of the
processes described above are carried out by hand. During the last
few decades many very large companies have been formed to take up
the production of bread on the large scale. This has caused almost
a revolution of the methods of manipulating flour and dough, and in
many cases nowadays almost every process in the bakery is carried out
by machinery. In many of the larger bakeries doughing and kneading
are carried out by machines, and this applies also to the processes
of scaling and moulding. A similar change has taken place too in the
construction of ovens. Years ago an oven consisted of a cavity in a
large block of masonry. Wood was burned in the cavity until the walls
attained a sufficiently high temperature. The remains of the fuel were
then raked out and the bread put in and baked by radiation from the hot
walls.
Nowadays it is not customary to burn fuel in the oven itself, nor is
the fuel always wood or even coal. The fuel is burned in a furnace
underneath the oven, and coal or gas is generally used. Sometimes
however the source of heat is electricity. In all cases it is still
recognised that the heat should be radiated from massive solid walls
maintained at a high temperature. In the latest type of oven the heat
is conducted through the walls by closed iron tubes containing water,
which of course at the high temperatures employed becomes superheated
steam. It is recognised that the ovens commonly provided in modern
private houses, whether heated by the fire of the kitchen range, or by
gas, are not capable of baking bread of the best quality, because their
walls do not radiate heat to the same degree as the massive walls of a
proper bake oven.
It is commonly agreed that bread, in the usual acceptation of the term,
should contain nothing but flour, yeast, salt, and water; or if other
things are present they should consist only of the products formed by
the interaction of these four substances in the process of baking.
Millers and bakers have, however, found by experience that the addition
of certain substances to the flour or to the dough may sometimes enable
them substantially to improve the market value of the bread produced by
certain flours. The possible good or bad effect of such additions on
the public health will be discussed in a later chapter. It may be of
interest here to mention some of the substances which are commonly used
as flour or bread improvers by millers and bakers, and to discuss the
methods by which they effect their so called improvements.
In a former chapter we have discussed the quality of wheat from the
miller’s point of view, and during the discussion certain views were
enunciated on the subject of strength. It was pointed out that a strong
flour was one which would make a large well-shaped loaf, and that the
size of the loaf was dependent on the flour being able to provide sugar
for the yeast to feed upon right up to the moment when the loaf goes
into the oven. This can only occur when the flour contains an active
ferment which keeps changing the starch into sugar. That this view is
generally accepted in practice is shown by the fact that, when using
flours deficient in such ferment, bakers commonly add to the flour,
yeast, salt, and water, a quantity of malt extract, the characteristic
constituent of which is the sugar producing ferment of the malt. This
use of malt extract is now extending to the millers, several of whom
have installed in their mills plant for spraying into their flour a
strong solution of malt extract. It seems to be agreed by millers and
bakers generally that such an addition to a flour which makes small
loaves distinctly increases the size of the loaf. There can be no doubt
that this effect is produced by the ferment of the malt extract keeping
up the supply of sugar, and thus enabling the yeast to maintain the
pressure of gas in the dough right up to the moment when it goes into
the oven.
The view that the shape of the loaf is due to the effect of salts, and
particularly of phosphates, on the coherence of the gluten has also
been put to practical use by the millers and the bakers. Preparations
of phosphates under various fancy names are now on the market, and are
bought by bakers for adding to the flour to strengthen the gluten and
produce more shapely loaves. A few millers too are beginning to spray
solutions of phosphates into their flours with the same object in view,
and such additions are said to make material improvements in the shape
of the loaf produced by certain weak flours.
These two substances, malt extract and phosphates, are added to the
flour with the definite object of improving the strength and thus
making larger and more shapely loaves. But there is a second class of
substances which are commonly added to flours, not in the mill but in
the process of bread making, with the object of replacing yeast. Yeast
is used in baking in order that it may form gas inside the dough and
thus produce a light spongy loaf. Exactly the same gas can be readily
and cheaply produced by the interaction of a carbonate with an acid.
These substances will not react to produce acid as long as they remain
dry, but as soon as they are brought into close contact with each other
by the presence of water, reaction begins and carbon dioxide gas is
formed. These facts are taken advantage of in the manufacture of baking
powders and self-rising flours. Baking powders commonly consist of
ordinary bicarbonate of soda mixed with an acid or an acid salt, such
as tartaric acid, cream of tartar, acid phosphate of lime, or acid
phosphate of potash. One of these latter acid substances is mixed in
proper proportions with the bicarbonate of soda, and the mixture ground
up with powdered starch which serves to dilute the chemicals and to
keep them dry. A small quantity of the baking powder is mixed with the
flour before the water is added to make the dough. The presence of the
water causes the acid and the carbonate to give off gas which, as in
the case of the gas formed by the growth of yeast, fills the dough with
bubbles which expand in the oven and produce light spongy bread. When
using baking powders in place of yeast it must not be forgotten that
gas formation in most cases begins immediately the water is added, and
lasts for a very short time. Consequently the dough must be moulded and
baked at once or the gas will escape. This is not the case, however,
with those powders which are made with cream of tartar, for this
substance does not react with the carbonate to any great extent until
the dough gets warm in the oven. For some purposes it is customary to
use carbonate of ammonia, technically known as volatile, in place of
baking powder. This substance is used alone without any addition of
acid, because it decomposes when heated and forms gas inside the dough.
Sometimes too one or other of the baking powders above described are
added to the flour by the miller, the product being sold as self-rising
flour. Such flour will of course lose its property of self-rising if
allowed to get damp. Occasionally objectionable substances are used in
making baking powders of self-rising flours. Some baking powders for
instance contain alum which is not a desirable addition to any article
of human food. Baking powders and self-rising flours are far more
frequently used by house-wives for making pastry or for other kinds of
domestic cookery than for breadmaking.
Bread is made on the large scale without the intervention of yeast
by the aeration process, which is carried out as follows. A small
quantity of malt is allowed to soak in a large quantity of water, and
the solution thus obtained is kept warm so that it may ferment. This
charges the solution with gas and at the same time produces other
substances which are supposed to give the bread a good flavour. Such a
solution too retains gas much better than pure water. This solution is
then mixed with a proper proportion of flour inside a closed vessel,
carbon dioxide gas made by the action of acid on a carbonate being
pumped into the vessel whilst the mixing is in progress. The mixing
is of course effected by mechanical means. As soon as the dough is
sufficiently mixed, it is allowed to escape by opening a large tap
at the bottom of the mixing vessel. This it does quite readily being
forced out by the pressure of gas inside. As it comes out portions of
suitable size to make a loaf are cut off. These are at once moulded
into loaves and put into the oven. The gas which they contain expands,
and light well risen bread is produced. This process is especially
suited for wholemeal and other flours containing much offal, which
apparently do not give the best results when submitted to the ordinary
yeast fermentation.
Before closing this chapter it may be of interest to add a short
account of the sale of bread. Bread is at the present time nominally
sold by weight under acts of Parliament passed about 80 years ago.
That is to say, a seller of bread must provide in his shop scales and
weights which will enable him to weigh the loaves he sells. No doubt
he would be prepared to do so if requested by a customer, in which
case he would probably make up any deficiency in weight which might be
found by adding as a makeweight a slice from another loaf. For this
purpose it is commonly accepted that the ordinary loaf should weigh two
pounds. But in practice this does not occur, for practically the whole
of the bread which is sold in this country is sold from the baker’s
cart, which delivers bread at the houses of customers, and not over
the counter. Customers obviously cannot be expected to wait at their
doors whilst the man in the cart weighs each loaf he is delivering
to them. In actual practice therefore the bread acts, as they are
called, are really a dead letter, and bread is sold by the loaf and
not by weight, though it must be remembered that the loaf has the
reputed weight of two pounds. There are no doubt slight variations
from this weight, but for all practical purposes competition nowadays
is quite as effective a check on the _bona fides_ of the bread seller
as enforced sale by weight would be likely to be. If a baker got the
reputation of selling loaves appreciably under weight his custom would
very soon be transferred to one of his more scrupulous competitors.
Altogether it may be concluded that the present unregulated method of
sale does not work to the serious disadvantage of the consumers. A
little consideration will show that the sale of bread could only be put
on a more scientific basis by the exercise of an enormous amount of
trouble, and the employment of a very numerous and expensive staff. No
doubt the ideally perfect way of regulating the sale of either bread
or any other feeding stuff would be to enact that it should be sold by
weight, and that the seller should be compelled to state the percentage
composition, so that the buyer could calculate the price he was asked
to pay per unit of actual foodstuff. Now bread normally contains 36
per cent. of water, but this amount varies greatly. A two pound loaf
kept in a dry place may easily lose water by evaporation at the rate of
more than an ounce a day. The baker usually weighs out 2 lbs. 3 ozs.
of dough to make each two pound loaf, and this amount yields a loaf
which weighs in most cases fully two pounds soon after it comes out
of the oven. But if the weather is hot and dry such a loaf may very
well weigh less than two pounds by the time it is delivered to the
consumer. In other words the baker cannot have the weight of the loaves
he sells under complete control. Furthermore the loss in weight when a
loaf gets dry by evaporation is due entirely to loss of water, and does
not decrease the amount of actual foodstuff in the loaf. To sell bread
in loaves guaranteed to contain a definite weight of actual foodstuff
might be justified scientifically, but practically it would entail
so great an expense for the salaries of the inspectors and analysts
required to enforce such a regulation that the idea is quite out of
the question. Practically, therefore, the situation is that it would
be unfair to enforce sale by weight pure and simple for the weight of
a loaf varies according to circumstances which are outside the baker’s
control, and further because the weight of the loaf is no guarantee of
the weight of foodstuff present in it. Nor is it possible to enforce
sale by guarantee of the weight of foodstuff in the loaf, for to do
so would be too troublesome and expensive. Finally the keenness of
competition in the baking trade may be relied on to keep an efficient
check on the interests of the consumer. Quite recently an important
public authority has published the results of weighing several
thousand loaves of bread purchased within its area of administration.
The results show that over half the two pound loaves purchased
were under weight to the extent of five per cent. on the average.
Legislation is understood to be suggested as the result of this report,
in which case it is to be hoped that account will be taken of the fact
that the food value of a loaf depends not only on its weight but also
on the percentage of foodstuffs and water which it contains.
CHAPTER VII
THE COMPOSITION OF BREAD
Bread is a substance which is made in so many ways that it is quite
useless to attempt to give average figures showing its composition. It
will suffice for the present to assume a certain composition which is
probably not far from the truth. This will serve for a basis on which
to discuss certain generalities as to the food-value of bread. The
causes which produce variation in composition will be discussed later,
together with their effect on the food value as far as information is
available. The following table shows approximately the composition of
ordinary white bread as purchased by most of the population of this
country.
per cent.
Water 36
Organic substances:
Proteins 10
Starch 42
Sugar, etc. 10
Fat 1
Fibre ·3 63·3
Ash:
Phosphoric acid ·2
Lime, etc. ·5 ·7
------
100·0
The above table shows that one of the most abundant constituents of
ordinary bread is water. Flour as commonly used for baking, although it
may look and feel quite dry, is by no means free from water. It holds
on the average about one-seventh of its own weight or 14 per cent. In
addition to this rather over one-third of its weight of water or about
35 to 40 per cent. is commonly required to convert ordinary flour into
dough. It follows from this that dough will contain when first it is
mixed somewhere about one-half its weight of water or 50 per cent.
About four per cent. of the weight of the dough is lost in the form
of water by evaporation during the fermentation of the dough before
it is scaled and moulded. Usually 2 lb. 3 oz. of dough will make a
two pound loaf, so that about three ounces of water are evaporated in
the oven, This is about one-tenth the weight of the dough or 10 per
cent. Together with the four per cent. loss by evaporation during the
fermenting period, this makes a loss of water of about 14 per cent.,
which, when subtracted from the 50 per cent. originally present in the
dough, leaves about 36 per cent. of water in the bread. As pointed out
in the previous chapter this quantity is by no means constant even in
the same loaf. It varies from hour to hour, falling rapidly if the loaf
is kept in a dry place.
To turn now to the organic constituents. The most important of these
from the point of view of quantity is starch, in fact this is the
most abundant constituent of ordinary bread. Nor is it in bread only
that starch is abundant. It occurs to the extent of from 50 to 70 per
cent. in all the cereals, grains, wheat, barley, oats, maize, and
rice. Potatoes too contain about 20 per cent. of starch, in fact it
is present in most plants. Starch is a white substance which does not
dissolve in cold water, but when boiled in water swells up and makes,
a paste, which becomes thick and semisolid on cooling. It is this
property which makes starch valuable in the laundry. Starch is composed
of the chemical elements carbon, hydrogen, and oxygen. When heated
in the air it will burn and give out heat, but it does not do so as
readily as does fat or oil. It is this property of burning and giving
out heat which makes starch valuable as a foodstuff. When eaten in the
form of bread, or other article of food, it is first transformed by
the digestive juices of the mouth and intestine into sugar, which is
then absorbed from the intestine into the blood, and thus distributed
to the working parts of the body. Here it is oxidized, not with the
visible flame which is usually associated with burning, but gradually
and slowly, and with the formation of heat. Some of this heat is
required to keep up the temperature of the body. The rest is available
for providing the energy necessary to carry on the movements required
to keep the body alive and in health. Practically speaking therefore
starch in the diet plays the same part as fuel in the steam engine. The
food value of starch can in fact be measured in terms of the quantity
of heat which a known weight of it can give out on burning. This is
done by burning a small pellet of starch in a bomb of compressed
oxygen immersed in a measured volume of water. By means of a delicate
thermometer the rise of temperature of the water is measured, and it
is thus found that one kilogram of starch on burning gives out enough
heat to warm 4·1 kilograms of water through one degree. The quantity of
heat which warms one kilogram of water through one degree is called one
unit of heat or calorie, and the amount of heat given out by burning
one kilogram of any substance is called its heat of combustion or
fuel-value. Thus the heat of combustion or fuel-value of starch is 4·1
calories.
Sugar has much the same food-value as starch, in fact starch is readily
changed into sugar by the digestive juices of the alimentary canal or
by the ferments formed in germinating seeds. From the point of view
of food-value sugar may be regarded as digested starch. Like starch,
sugar is composed of the elements carbon, hydrogen, and oxygen. Like
starch too its value in nutrition is determined by the amount of heat
it can give out on burning, and again its heat of combustion or fuel
value 3·9 calories is almost the same as that of starch. It will be
noted that the whole of the 10 per cent. quoted in the table as sugar,
etc., is not sugar. Some of it is a substance called dextrin which is
formed from starch by the excessive heat which falls on the outside of
the loaf in the oven. Starch is readily converted by heat into dextrin,
and this fact is applied in many technical processes. For instance much
of the gum used in the arts is made by heating starch. The outside
of the loaf in the oven gets hot enough for some of the starch to be
converted into dextrin. Dextrin is soluble in water like sugar and so
appears with sugar in the analyses of bread. From the point of view of
food-value this is of no consequence, as dextrin and sugar serve the
same purpose in nutrition, and have almost the same value as each other
and as starch.
Bread always contains a little fat, not as a rule more that one or two
per cent. But although the quantity is small it cannot be neglected
from the dietetic point of view. Fat is composed of the same elements
as starch, dextrin, and sugar, but in different proportions. It
contains far less oxygen than these substances. Consequently it burns
much more readily and gives out much more heat in the process. The heat
of combustion or fuel value of fat is 9·3 calories or 2·3 times greater
than that of starch. Evidently therefore even a small percentage of
fat must materially increase the fuel value of any article of food.
But fat has an important bearing on the nutritive value of bread from
quite another point of view. In the wheat grain the fat is concentrated
in the germ, comparatively little being present in the inner portion
of the grain. Thus the percentage of fat in any kind of bread is on
the whole a very fair indication of the amount of germ which has been
left in the flour from which the loaf was made. It is often contended
nowadays that the germ contains an unknown constituent which plays an
important part in nutrition, quite apart from its fuel-value. On this
supposition the presence of much fat in a sample of bread indicates the
presence of much germ, and presumably therefore much of this mysterious
constituent which is supposed to endow such bread with a special value
in the nutrition particularly of young children. This question will be
discussed carefully in a later chapter.
White bread contains a very small percentage of what is called by
analysts fibre. The quantity of this substance in a food is estimated
by the analyst by weighing the residue which remains undigested when a
known weight of the food is submitted to a series of chemical processes
designed to imitate as closely as may be the action of the various
digestive juices of the alimentary canal. Theoretically, therefore,
it is intended to represent the amount of indigestible matter present
in the food in question. Practically it does not achieve this result
for some of it undoubtedly disappears during the passage of the
food through the body. It is doubtful however if the portion which
disappears has any definite nutritive value. That part of the fibre
which escapes digestion and is voided in the excrement cannot possibly
contribute to the nutrition of the body. Nevertheless it exerts a
certain effect on the well-being of the consumer, for the presence of
a certain amount of indigestible material stimulates the lower part of
the large intestine and thus conduces to regularity in the excretion
of waste matters, a fact of considerable importance in many cases.
The amount of fibre is an index of the amount of indigestible matter
in a food. In white bread it is small. In brown breads which contain
considerable quantities of the husk of the wheat grain it may be
present to the extent of two or three per cent. Such breads therefore
will contain much indigestible matter, but they will possess laxative
properties which make them valuable in some cases.
We have left to the last the two constituents which at the present time
possess perhaps the greatest interest and importance, the proteins
and the ash. The proteins of bread consist of several substances, the
differences between which, for the present purpose, may be neglected,
and we may assume that for all practical purposes the proteins of bread
consist of one substance only, namely gluten. The importance of gluten
in conferring on wheat flour the property of making light spongy loaves
has already been insisted upon. No doubt this property of gluten has a
certain indirect bearing on the nutritive value of bread by increasing
its palatability. But gluten being a protein has a direct and special
part to play in nutrition, which is perhaps best illustrated by
following one step further the comparison between the animal body and
a steam engine. It has been pointed out that starch, sugar, and fat
play the same part in the body as does the fuel in a steam engine. But
an engine cannot continue running very long on fuel alone. Its working
parts require renewing as they wear away, and coal is no use for this
purpose. Metal parts must be renewed with metal. In much the same way
the working parts of the animal body wear away, and must be renewed
with the stuff of which they are made. Now the muscles, nerves, glands
and other working parts of the body are made of protein, and they can
only be renewed with protein. Consequently protein must be supplied in
the diet in amount sufficient to make good from day to day the wear and
tear of the working parts of the body. It is for this reason that the
protein of bread possesses special interest and importance.
Protein like starch, sugar, and fat contains the elements carbon,
hydrogen, and oxygen, but it differs from them in containing also
a large proportion of the element nitrogen, which may be regarded
as its characteristic constituent. When digested in the stomach and
intestine it is split into a large number of simpler substances known
by chemists under the name of amino-acids. Every animal requires these
amino-acids in certain proportions. From the mixture resulting from
the digestion of the proteins in its diet the amino-acids are absorbed
and utilised by the body in the proportions required. If the proteins
of the diet do not supply the amino-acids in these proportions, it is
obvious that an excessive amount of protein must be provided in order
that the diet may supply enough of that particular amino-acid which
is present in deficient amount, and much of those amino-acids which
are abundantly present must go to waste. This is undesirable for
two reasons. Waste amino-acids are excreted through the kidneys, and
excessive waste throws excessive work on these organs, which may lead
to defective excretion, and thus cause one or other of the numerous
forms of ill health which are associated with this condition. Again,
excessive consumption of protein greatly adds to the cost of the diet,
for protein costs nearly as many shillings per pound as starch or sugar
costs pence.
These considerations show clearly the wisdom of limiting the amount
of protein in the diet to the smallest amount which will provide for
wear and tear of the working parts. The obvious way to do this is to
take a mixed diet so arranged that the various articles of which the
diet consists contain proteins which are so to speak complementary.
The meaning of this is perhaps best illustrated by a concrete example.
The protein of wheat, gluten, is a peculiar one. On digestion it
splits like other proteins into amino-acids, but these are not present
from the dietetic point of view in well balanced proportions. One
particular amino-acid, called glutaminic acid, preponderates, and
unfortunately this particular acid does not happen to be one which the
animal organism requires in considerable quantity. Other amino-acids
which the animal organism does require in large amounts are deficient
in the mixture of amino-acids yielded by the digestion of the protein
of wheat. It follows, therefore, that to obtain enough of these latter
acids a man feeding only on wheat products would have to eat a quantity
of bread which would supply a great excess of the more abundant
glutaminic acid, which would go to waste with the evil results already
outlined. From this point of view it appears that bread should not
form more than a certain proportion of the diet, and that the rest of
the diet should consist of foods which contain proteins yielding on
digestion little glutaminic acid and much of the other amino-acids in
which the protein of wheat is deficient. Unfortunately information
as to the exact amount of the different amino-acids yielded by the
digestion of the proteins even of many of the common articles of food
is not available. But many workers are investigating these matters, and
the next great advance in the science of dietetics will probably come
along these lines. By almost universal custom certain articles of food
are commonly eaten in association: bread and cheese, eggs and bacon,
are instances. Such customs are usually found to be based on some
underlying principle. The principle in this case may well be that of
complementary proteins.
The remarks which have been made above on the subject of the _rôle_
of protein in the animal economy apply to adults in which protein
is required for wear and tear only and not for increase in weight.
They will obviously apply with greatly increased force to the case of
growing children, who require protein not only for wear and tear, but
for the building up of their muscles and other working parts as they
grow and develope. Consequently the diet of children should contain
more protein in proportion to their size than that of adults. For
this reason it is not desirable that bread should form an excessive
proportion of their diet. The bread they eat should be supplemented
with some other food richer in protein.
The ash of bread although so small in amount cannot be ignored, in
fact it is regarded as of very great importance by modern students
of dietetics. The particular constituent of the ash to which most
importance is attached is phosphoric acid. This substance is a
necessary constituent of the bones and of the brain and nerves of all
animals. It exists too in smaller proportions in other organs. Like
other working parts of the body the bones and the nervous system are
subject to wear and tear, which must be replaced if the body is to
remain in normal health. A certain daily supply of phosphoric acid is
required for this purpose, and proportionally to their size more for
children than for adults. Considerable difference of opinion as to the
exact amount required is expressed by those who have investigated this
question, nor is it even agreed whether all forms of phosphoric acid
are of the same value. There is however a general recognition of the
importance of this constituent of the diet, and the subject is under
investigation in many quarters.
CHAPTER VIII
CONCERNING DIFFERENT KINDS OF BREAD
The table given in the last chapter states the average composition
of ordinary white bread baked in the form of cottage loaves, and the
remarks on the various constituents of bread in the preceding pages
have for the most part referred to the same material, though many of
them may be taken to refer to bread in general. It will now be of
interest to inquire as to the variation in composition which is found
among the different kinds of bread commonly used in this country.
This enquiry will be most readily conducted by first considering the
possible causes which may affect the composition of bread.
The variation in the composition of bread is a subject which is taken
up from time to time by the public press, and debated therein with a
great display of interest and some intelligent knowledge. In most of
the press discussions in the past interest has been focussed almost
entirely on the effect of different kinds of milling. The attitude
commonly assumed by the food reform section of the contributors may be
stated shortly as follows: In the days of stone milling a less perfect
separation of flour and bran was effected, and the flour contained
more of the materials situated in the grain near the husk than do the
white flours produced by modern methods of roller milling. Again the
modern roller mills separate the germ from the flour, which the stone
mills fail to do, at any rate so completely. Thus the stone ground
flours contain about 80 per cent. of the grain, whilst the whole of the
flour obtained from the modern roller mill seldom amounts to much more
than about 72 per cent. The extra eight per cent. of flour produced
in the stone mills contains all or nearly all the germ and much of
the material rich in protein which lies immediately under the husk.
Hence the stone ground flour is richer in protein, and in certain
constituents of the germ, than white roller mill flour, and hence again
stone ground flour has a higher nutritive value. Roller mill flour has
nothing to commend it beyond its whiteness. It has been suggested that
millers should adopt the standard custom of producing 80 per cent. of
flour from all the wheat passing through their mills and thus retain
those constituents of the grain which possess specially great nutritive
value.
It would probably be extremely difficult to produce 80 per cent. of
flour from many kinds of wheat, but for the present this point may
be ignored, whilst we discuss the variation in the actual chemical
composition of the flour produced as at present and on the 80 per cent.
basis. In comparing the chemical composition of different kinds of
flour it is obvious that the flours compared must have been made from
the same lot of wheat, for as will be seen later different wheats vary
greatly in the proportions of protein and other important constituents
which they contain. Unfortunately the number of analyses of different
flours made from the same lots of wheat is small. Perhaps the best
series is that published by Dr Hamill in a recent report of the Local
Government Board. Dr Hamill gives the analyses of five different grades
of flour made at seven mills, each mill using the same blend of wheats
for all the different kinds of flour. Calculating all these analyses
to a basis of 10 per cent. of protein in the grade of flour known as
patents, the figures on the opposite page were obtained, which may be
taken to represent with considerable accuracy the average composition
of the various kinds of flours and offals when made from the same wheat.
Description of flour Protein Phosphoric acid
or offal per cent. per cent.
Flours:
Patents 10·0 0·18
Straight grade, about 70 per cent. 10·6 0·21
Households 10·9 0·26
Standard flour, about 80 per cent. 11·0 0·35
Wholemeal 11·3 0·73
Offals:
Germ 24·0 2·22
Sharps 14·5 1·66
Bran 13·5 2·50
Accepting these figures as showing the relative proportions of protein
and phosphoric acid in different flours as affected by milling only,
other sources of variation having been eliminated by the use of the
same blend of wheat, it appears that the flours of commercially higher
grade undoubtedly do contain somewhat less protein and phosphoric
acid than lower grade or wholemeal flours. Taking the extreme cases
of patents and wholemeal flours, the latter contains one-ninth more
protein and four times more phosphoric acid than the former, provided
both are derived from the same wheat.
In actual practice, however, it generally happens that the higher
grade flours are made from a blend of wheats containing a considerable
proportion of hard foreign wheats which are rich in nitrogen, whilst
wholemeal and standard flours are usually made from home grown wheats
which are relatively poor in nitrogen. From a number of analyses of
foreign and home grown wheats it appears that the relative proportions
of protein is about 12½ per cent. in the hard foreign wheats as
compared with 10 per cent. in home grown wheats. Thus the presence
of a larger proportion of protein in the hard wheats used in the
blend of wheat for making the higher grade flours must tend to reduce
the difference in protein content between say patents and wholemeal
flours as met with in ordinary practice. Furthermore much of the bread
consumed by that part of the population to whom a few grams per day
of protein is of real importance is, or should be, made, for reasons
of economy, from households flour, and the disparity between this
grade of flour and wholemeal flour is much less than is the case with
patents. It appears, therefore, on examining the facts, that there is
no appreciable difference in the protein content of the ordinary white
flours consumed by the poorer classes of the people and wholemeal flour
or standard flour.
In the above paragraphs account has been taken only of the total amount
of protein in the various kinds of bread and flour. It is obvious,
however, that the total amount present is not the real index of
food-value. Only that portion of any article of diet which is digested
in the alimentary canal can be absorbed into the blood and carried
thereby to the tissues where it is required to make good wear and tear.
The real food-value must therefore depend not on the total amount of
foodstuff present but on the amount which is digestible. The proportion
of protein which can be digested in the different kinds of bread
has been the subject of careful experiments in America, and lately
in Cambridge. The method of experimenting is arduous and unpleasant.
Several people must exist for a number of days on a diet consisting
chiefly of the kind of bread under investigation, supplemented only by
small quantities of food which are wholly digestible, such as milk,
sugar and butter. During the experimental period the diet is weighed
and its protein content estimated by analysis. The excreta are also
collected and their protein content estimated by analysis, so that
the amount of protein which escapes digestion can be ascertained.
The experiment is then repeated with the same individuals and the
same conditions in every way except that another kind of bread is
substituted for the one used before. From the total amount of protein
consumed in each kind of bread the total amount of protein voided
in the excreta is subtracted, and the difference gives the amount
which has been digested and presumably utilised in the body. From
these figures it is easy to calculate the number of parts of protein
digested for every 100 parts of protein eaten in each kind of bread.
This description will have made evident the unpleasant nature of such
experimental work. Its laboriousness will be understood from the fact
that a series of experiments of this kind carried out at Cambridge last
winter necessitated four people existing for a month on the meagre
diet above mentioned, and entailed over 1000 chemical analyses.
The following table shows the amounts of protein digested per 100 parts
of protein consumed in bread made from various kinds of flour, as based
on the average of a number of experiments made in America, and in the
experiments at Cambridge above referred to.
Kind of flour from Percentage of Amount of protein digested
which bread the grain per 100 parts eaten
was made contained in American Cambridge
the flour experiments experiments
Patents 36 -- 89
Straight grade 70 89 --
Standard 80 81 86
Brown 88 -- 80
Brown 92 -- 77
Wholemeal 100 76 --
The American and the Cambridge figures agree very well with each other,
and this gives confidence in the reliability of the results. It appears
to be quite certain therefore that the protein in bread made from the
higher grade flours is very considerably more digestible than that
contained in bread made from flours containing greater amounts of husk.
The percentages following the names of the various grades of flour in
the first column of the table indicate approximately the proportion
of the whole grain which went into the flour to which the figure is
attached. Looking down these figures it appears that the digestibility
of the protein decreases as more and more of the grain is included in
the flour. It follows, therefore, that whilst by leaving more and more
of the grain in the flour we increase the percentage of protein in the
flour, and consequently in the bread, at the same time we decrease
the digestibility of the protein. Apparently, too, this decrease in
digestibility is proportionally greater than the increase in protein
content, and it follows therefore that breads made from low grade
flours containing much husk will supply less protein which is available
for the use of the body, although they may actually contain slightly
more total protein than the flours of higher grade.
When all the facts are taken into account it appears that the
contention of the food reformers, that the various breads which contain
those constituents of the grain which lie near the husk are capable of
supplying more protein for the needs of the body than white breads,
cannot be upheld. From statistics collected by the Board of Trade some
few years ago as to the dietary of the working classes it appears that
the diet of workers both in urban and in rural districts contains
about 97 grams of total protein per head per day. This is rather under
than over the commonly accepted standard of 100 grams of protein which
is supposed to be required daily by a healthy man at moderate work.
Consequently a change in his diet which increased the amount of protein
might be expected to be a good change. But the suggested change of
brown bread for white, though it appears to increase the total protein,
turns out on careful examination to fail in its object, for it does not
increase the amount of protein which can be digested.
From the same statistics it appears that the diet of a working man
includes on the average about 1¼ lb. of bread per day. This amount of
bread contains about 60 grams of protein, or two-thirds of the total
protein of the diet. Now it was pointed out in the last chapter that
the protein of wheat was very rich in glutaminic acid, a constituent
of which animals require comparatively small amounts. It is also
correspondingly poor in certain constituents which are necessary to
animals. Apparently therefore it would be better to increase the diet
in such cases by adding some constituent not made from wheat than by
changing the kind of bread. From the protein point of view, however we
look at it, there appears to be no real reason for substituting one or
other of the various kinds of brown bread for the white bread which
seems to meet the taste of the present day public.
But important as protein is it is not everything in a diet. As we have
already pointed out the food must not only repair the tissues, it must
also supply fuel. It has been shown also that the fuel-value of a food
can be ascertained by burning a known weight and measuring the number
of units of heat or calories produced. Many samples of bread have been
examined in this way in the laboratories of the American Department of
Agriculture, and it appears from the figures given in their bulletins
that the average fuel value of white bread is about 1·250 calories per
pound, of wholemeal bread only 1·150 calories per pound. These figures
are quite in accord with those which were obtained in Cambridge in
1911, in connection with the digestion experiments already described,
which were also extended so as to include a determination of the
proportion of the energy of the bread which the diet supplied to the
body. The energy or fuel-value of the diet was determined by measuring
the amount of heat given out by burning a known weight of each of
the kinds of bread used in the experiment. The energy which was not
utilised by the body was then determined by measuring how much heat was
given out by burning the excreta corresponding to each kind of bread.
The following table gives side by side the average results obtained in
several such experiments in America and in Cambridge.
The agreement between the two sets of figures is again on this point
quite satisfactory. It is evident that a greater proportion of the
total energy of white bread can be utilised by the body than is the
case with any of the breads made from flours of lower commercial grades
which contain more husk. In fact it appears that the more of the outer
parts of the grain are left in the flour the smaller is the proportion
of the total energy of the bread which can be utilised. Combining this
conclusion with the fact that brown breads contain on the average less
total energy than white breads, there can be no doubt that white bread
is considerably better than any form of brown bread as a source of
energy for the body.
Kind of flour from Percentage of Amount of energy utilised
which the bread the grain per 100 units in food
was made contained in American Cambridge
the flour experiments experiments
Patents 36 96 96
Straight grade 70 92 --
Standard 80 87 95
Brown 88 -- 90
Brown 92 -- 89
Wholemeal 100 82 --
There is one more important substance in respect of which great
superiority is claimed for brown breads, namely phosphoric acid. From
the table on page 122 there can be no doubt that flours containing more
of the outer parts of the grain are very much richer in phosphoric
acid than white flours, and the disparity is so great that after
allowing for the larger proportion of water in brown breads they
must contain far more of this substance than do white breads. In the
Cambridge digestibility experiments quoted above the proportion of the
phosphoric acid digested from the different breads was determined. It
was found that for every 100 parts of phosphoric acid in white bread
only 52 parts were digested, and that in the case of the brown breads
this proportion fell to 41 parts out of 100. Again, as in the case of
protein and energy, the phosphoric acid in white bread is more readily
available to the body than that of brown bread, but in this case the
difference in digestibility is not nearly enough to counterbalance
the much larger proportion of phosphoric acid in the brown bread.
There is no doubt that the body gets more phosphoric acid from brown
bread than from the same quantity of white bread. But before coming
to any practical conclusion it is necessary to know two things, how
much phosphoric acid does a healthy man require per day, and does his
ordinary diet supply enough?
From the Board of Trade statistics already quoted it appears that,
on the assumption that the average worker eats white bread only, his
average diet contains 2·4 grams of phosphoric acid per day, which would
be raised to 3·2 grams if the white bread were replaced by bread made
from 80 per cent. flour containing ·35 per cent. of phosphoric acid.
Information as to the amount of phosphoric acid required per day by
a healthy man is somewhat scanty, and indicates that the amount is
very variable, but averages about 2½ grams per day. If this is so,
the ordinary diet with white bread provides on the average enough
phosphoric acid. Exceptional individuals may, however, be benefited by
the substitution of brown bread for white, but it would probably be
better even in such cases, for the reasons stated when discussing the
protein question, to raise the phosphorus content of their diet by the
addition of some substance rich in phosphorus but not made from wheat.
Finally comes the question of the variation in the composition of
bread due to the presence or absence of the germ. The first point in
this connection is to decide whether germ is present in appreciable
proportions in any flour except wholemeal. The germ is a soft moist
substance which flattens much more readily than it grinds. Consequently
it is removed from flour by almost any kind of separation, even when
very coarse sieves are employed. If this contention is correct no flour
except wholemeal should contain any appreciable quantity of germ, and
it is certainly very difficult to demonstrate the presence of actual
germ particles even in 80 per cent. flour. Indirect evidence of the
presence of germ may, however, be obtained as already explained by
estimating by chemical analysis the proportion of fat present in
various flours. The figures for such estimations are given by Dr Hamill
in the report of the Local Government Board already referred to. They
show that the percentages of fat in different grades of flours made
from the same blends of wheat are on the average of seven experiments
as follows: patents flour ·96: household flours 1·25: 80 per cent.
or standard flour 1·42. These figures show that the coarser flours
containing more of the whole grain do contain more germ than the flours
of commercially higher grade, in spite of the fact that it is difficult
to demonstrate its presence under the microscope.
Remembering, however, that the whole of the germ only amounts to about
1½ per cent. of the grain, it is clear that the presence or absence of
more or less germ cannot appreciably affect the food-value as measured
by protein content or energy-value. It is still open to contention that
the germ may contain some unknown constituent possessing a peculiar
effect on nutrition. Such a state of things can well be imagined in the
light of certain experimental results which have been obtained during
the last few years.
It has been shown for instance by Dr Hopkins in Cambridge, and his
results have been confirmed at the Carnegie Institute in America, that
young rats fail to thrive on a diet composed of suitable amounts of
purified protein, fat, starch, and ash, but that they thrive and grow
normally on such a diet if there is added a trace of milk or other
fresh animal or vegetable substance far too small to influence either
the protein content or the energy-value. Another case in point is the
discovery that the disease known as beri beri, which is caused by a
diet consisting almost exclusively of rice from which the husk has been
removed, can be cured almost at once by the administration of very
small doses of a constituent existing in minute quantities in rice
husk. The suggestion is that high grade flours, like polished rice, may
fail to provide some substance which is necessary for healthy growth,
a substance which is removed in the germ or husk when such flours are
purified, and which is present in flours which have not been submitted
to excessive purification.
The answer is that no class in Great Britain lives on bread
exclusively. Bread appears from the government statistics already
quoted to form only about half the diet of the workers of the country.
Their diet includes also some milk, meat, and vegetables, and such
substances, according to Dr Hopkins’ experiments, certainly contain the
substance, whatever it may be, that is missing from the artificial diet
on which his young rats failed to thrive.
One last point. It will have been noticed in the figures given
above that the variations in protein content, digestibility, and
energy-value, between different kinds of bread are usually not
very large. There is, however, one constituent of all breads whose
proportions vary far more widely, namely water. During last summer the
author purchased many samples of bread in and around Cambridge, and
determined the percentage of water in each sample. The samples were all
one day old so that they are comparable with one another. The results
on the whole are a little low, probably because the work was done
during a spell of rather dry weather, when the loaves would lose water
rapidly.
The average figures are summarised below:
Percentage
of water
Cottage loaves made of white flour 31·7
Tinned loaves made of white flour 32·7
Small fancy loaves made of white flour 33·7
Tinned loaves made of “Standard” flour 35·9
Tinned loaves made of brown or germ flour 40·0
The figures speak for themselves. There must obviously be more actual
food in a cottage loaf of white flour containing under 32 per cent.
of water than in any kind of Standard or brown loaf in which the
percentage of water is 36 to 40. It is quite extraordinary that no one
who has organised any of the numerous bread campaigns in the press
appears to have laid hold of the enormous variation in the water
content of different kinds of bread, and its obvious bearing on their
food-value.
BIBLIOGRAPHY
The reader who wishes further information on any of the numerous
subjects connected with the growth, manipulation and composition of
breadstuffs is referred to the following publications, to which among
others the author is much indebted. The list is arranged, as far as
possible, in the same order as the chapters of the book.
CHAPTER I.
The Book of the Rothamsted Experiments, by A. D. Hall. (John
Murray, 1905.)
The Feeding of Crops and Stock, by A. D. Hall. (John Murray,
1911.)
Fertilizers and Manures, by A. D. Hall. (John Murray, 1909.)
The Soil, by A. D. Hall. (John Murray, 1908.)
Agriculture and Soils of Kent, Surrey, and Sussex, by A. D.
Hall and E. J. Russell. (Board of Agriculture and Fisheries.)
Some Characteristics of the Western Prairie Soils of Canada,
by Frank T. Shutt. (_Journal of Agricultural Science_, Vol.
III, p. 335.)
Dry Farming: its Principles and Practice, by Wm Macdonald. (T.
Werner Laurie.)
Profitable Clay Farming, by John Prout. (1881.)
Continuous Corn Growing, by W. A. Prout and J. Augustus
Voelcker. (_Journal of the Royal Agricultural Society of
England_, 1905.)
CHAPTER II.
The Wheat Problem, by Sir W. Crookes. (John Murray, 1899.)
The Production of Wheat in the British Empire, by A. E.
Humphries. (_Journal of the Royal Society of Arts_, Vol.
LVII, p. 229.)
Wheat Growing in Canada, the United States, and the Argentine,
by W. P. Rutter. (Adam and Charles Black, 1911.)
Agricultural Note-Book, by Primrose McConnell. (Crosby,
Lockwood and Son, 1910.)
CHAPTER III.
Agricultural Botany, by J. Percival. (Duckworth and Co., 1900.)
The Interpretation of the Results of Agricultural Experiments,
by T. B. Wood, and Field Trials and their interpretation,
by A. D. Hall and E. J. Russell. (_Journal of the Board of
Agriculture and Fisheries_, Supplement No. 7, Nov. 1911.)
Heredity in Plants and Animals, by T. B. Wood and R. C.
Punnett. (_Journal of the Highland and Agricultural Society of
Scotland_, Vol. XX, Fifth Series, 1908.)
Mendelism, by R. C. Punnett. (Macmillan and Co., 1911.)
Mendel’s Laws and Wheat Breeding, by R. H. Biffen. (_Journal of
Agricultural Science_, Vol. I, p. 4.)
Studies in the Inheritance of Disease Resistance, by R. H.
Biffen. (_Journal of Agricultural Science_, Vol. II,
p. 109; Vol. IV, p. 421.)
The Inheritance of Strength in Wheat, by R. H. Biffen.
(_Journal of Agricultural Science_, Vol. III, p. 86.)
Variation, Heredity, and Evolution, by R. H. Lock. (John
Murray, 1909.)
Minnesota Wheat Breeding, by Willet M. Hays and Andrew Boss.
(McGill-Warner Co., St Paul.)
The Improvement of English Wheat, by A. E. Humphries and R. H.
Biffen. (_Journal of Agricultural Science_, Vol. II,
p. 1.)
Plant Breeding in Scandinavia, by L. H. Newman. (The Canadian
Seed Growers Association, Ottawa, 1912.)
CHAPTERS IV, V, AND VI.
The Technology of Bread Making, by W. Jago. (Simpkin, Marshall
and Co., 1911.)
Modern Development of Flour Milling, by A. E. Humphries.
(_Journal of the Royal Society of Arts_, Vol. LV, p.
109.)
Home Grown Wheat Committee’s Reports. (59, Mark Lane, London,
E.C.)
The Chemistry of Strength of Wheat Flour, by T. B. Wood.
(_Journal of Agricultural Science_, Vol. II, pp. 139,
267.)
CHAPTERS VII AND VIII.
Composition and Food Value of Bread, by T. B. Wood. (_Journal
of the Royal Agricultural Society of England_, 1911.)
Some Experiments on the Relative Digestibility of White and
Whole-meal Breads, by L. F. Newman, G. W. Robinson, E. T.
Halnan, and H. A. D. Neville. (_Journal of Hygiene_, Vol.
XII, No. 2.)
Nutritive Value of Bread, by J. M. Hamill. (_Local Government
Board Report_, Cd. 5831.)
Bleaching and Improving Flour, by J. M. Hamill and G. W. Monier
Williams. (_Local Government Board Report_, Cd. 5613.)
Diet of Rural and Urban Workers. (_Board of Trade Reports_, Cd.
1761 and 2337.)
Bulletins of the U.S.A. Department of Agriculture. (Division
of Chemistry 13; Office of Experiment Stations 21, 52, 67, 85,
101, 126, 156, 185, 227.)
INDEX
Aerated bread, 104
Amino-acids, 116
Ash of bread, 119
Baking, 63, 91
Baking powders, 102
Biffen’s new varieties, 49, 59
method, 41, 46, 58
Bread, amount in diet, 127
composition of, 109
variations in, 120
water in, 135
Break rolls, 81
Breeding of wheat, 29, 35, 40
Burgoyne’s Fife, 59
Climate suitable for wheat, 2, 28
Clover as preparation for wheat, 8
Colloids, 67
Continuous growth of wheat, 7
Crookes, Sir W., shortage of nitrogen, 5
Cropping power of wheats, 32
Cross-breeding, 40
Digestibility of bread, 124
Dressing wheat, 16
Dry farming, 10
Elements required by wheat, 2
Energy-values, 111
Fat in bread, 113
Fermentation in dough, 94
Fibre, 114
Field plots, accuracy of, 32
Fife wheat, 47, 57
Flour, composition of, 122
grades of, 88, 122
self-rising, 102
Food-value of various breads, 120
of starch, etc. in bread, 110
Foreign wheat growing, 21
Fuel-values, 111
Futures, 26
Germ, food-value of, 132
in milling, 89
in bread, 114, 132
Gluten, 63
properties of, 68
Grades of flour, 88, 122
of wheat, 23
Home Grown Wheat Committee, 53, 56
Hopkins’ work, 132
Hybridisation, 40
Improvers, flour, 100
Indigestible matter in bread, 114
Inheritance in wheat, 41
Johannsen, 37
Judging wheats, 60
Lawes and Gilbert, 4
Liebig, 3
Little Joss wheat, 51
Manuring wheat, 3, 7
Markets, home, 16
foreign, 22, 27
Market quotations, 19
Mendel’s laws, 40
Milling, history of, 74, 77
effect of, on flour, 122
Mineral manures, 3
Minnesota experiments, 36
Natural moisture in wheat, 52
Nitrogen, cost of, in manures, 4
fixation, 8
for wheat, 4
from air, 6
scarcity of, 5
synthetic, 6
Ovens for baking, 99
Patents flour, 88
Pedigree in wheat, 39
Phosphates in bread, 119
in diet, 131
in flour, 70
Plots for yield testing, 32
Protein, cost of, in diet, 116
in bread, 115
Prout’s system of farming, 7
Pure-line theory, 37
Purification of flour, 86
Rainfall for wheat, 2
Red Fife, 47
Reduction rolls, 87
Roller mill, 79
Rotation of crops, 9
Rothamsted experiments, 4
Rust-proof wheat, 51
Sale of bread, 105
of wheat, 16
Scaling loaves, 96
Selection for cropping power, 35
Self-rising flour, 102
Separation of flour, 85
Semolina, 86
Sheep-folding, 10
Soils for wheat, 2
“Standard” flour, 135
Starch in bread, 110
Stone mill, 75
Strength of flour, cause of, 62
of flour, test for, 66, 72
of wheat or flour, 53
Strong wheats, characters of, 60
value of, 59
Sugar in bread, 112
Synthetic nitrogenous manures, 6
Thrashing wheat, 15
Turbidity test for strong wheats, 73
Variety of wheat, choice of, 28
testing, 32
Virgin soils, 5
Water in bread, 109, 135
Weak wheats, characters of, 61
Weights and measures, 17
Yeast, growth in dough, 94
Yield of wheat, conditions of, 28
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Transcriber's Note:
Page 11, 12. “Olland” defined in 1863 by John Morton thus:
Olland (Nors., Suff.) arable land which has been laid down to clover or
grass, for two years.
Inconsistent spelling and hyphenation are as in the original.
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