[Transcriber's Note:
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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.