The technology of bread-making : including the chemistry and analytical and practical testing of wheat, flour, and other materials employed in bread-making and confectionery

Front matter

LIBRARY

64-1

Jl8t

Preface

The volume now offered to the reader must be regarded as a development of the vTiter’s former works on the same subject, which appeared in 1886 and 1895. The general mode of treatment is, therefore, to some extent governed by that of its predecessors. It should be remembered that the requirements of the student of the technology of bread-making, whether miller or baker, have been the first consideration ; and accordingly the arrangement is that which seems most likely to be of service and assistance to him. In addition the authors have endeavoured to make the book as complete a work of general reference as possible.

In the preparation of the present treatise the wTiter has had the benefit of the assistance of his son, Mr. William C. Jago, whose name, together with his ^ own, appears on the title-page. Mx. William C. Jago’s wide experience of ' the practical application of chemical methods in the mill and the factory r have been of much advantage. So also has been his knowledge of the dairying industries gained in Denmark, and of modern biology and bacteriology acquired in the laboratories of Professor Jorgensen in Copenhagen. The writer is further indebted to him for the investigation and verification of many references in the original French, German, and Danish.

Since 1895 much valuable original work has been done in this country, ^ and also in Europe and America, on bread-making and cognate subjects. The authors have tried to place this as fully as possible on record. In so doing they have adopted the method of giving a resume of each investiga- - tor’s work and conclusions, following the same where necessary by any

j

7 comments of their own. In pursuance of this plan, new chapters have been i wTitten on the Strength of Flour, the Bleaching of Flour, Wheat Flour and ] Bread Improvers, the Nutritive Value and Digestibility of Bread, and the I Weighing of Bread. Subjects such as “ Standard ” Bread, and the use of

V

199817

PREFACE.

additions to flour and bread have been critically and exhaustively examined. The application of chemical and other tests to routine mill practice has been dealt with in a special chapter. Following on the inclusion of Confectionery in the programme of the City and Guilds of London Institute for the Advancement of Technical Education, a chapter has been added on the Chemistry of the Confectioners’ Raw Materials and Processes.

Again, the authors desire to express their thanks to the number of millers, bakers, and scientists who by personal communications and in many other ways have rendered them so much assistance in the preparation of this volume. The numerous instances of help of this kind will be evident on a perusal of the following pages.

In a work of such magnitude, the authors cannot hope to have altogether avoided mistakes, and in such cases they confldently appeal to the generous consideration of their readers.

WILLIAM JAGO.

London, E.C.,

1, Garden Court, Temple, July, 1911.

Contents

CHAPTER

PAGE

I Introductory ..........

Chapter I. Introductory

1. General Scope of Work. — ^The object of the present Work is to deal, in the first place, with those branches of knowledge which together constitute the scientific foundations of Bread-making as a science in itself. Paramount among these is —

Chemistry.

With which is closely associated —

Heat and its properties.

Fermentation and the Biology of Micro-organisms.

Vegetable Physiology in its relation to the Wheat Plant.

Microscopy.

Next, viewing Bread-making as an Art or Industry, the design of Bakeries and adaptation of Machinery for various purposes is discussed. Following on this is a description of the various processes and operations involved in the Commercial Manufacture of Bread, together with an investigation of the many important practical problems connected therewith. Chapters are also added on the nutritive value, and weighing, of bread, and other matters of interest.

The more purely analytical section of the work includes detailed diiections foi the commercial testing and valuation of flour, yeast, and other bread-making materials ; in addition to which there are also given approved methods for the commercial and complete chemical analysis of such substances. A number of analyses and other chemical investigations have been recently made for the purposes of this book, and are here for the first time published. The work concludes with a description of the chemistry of confectioners’ raw materials.

It is not proposed to adhere to any very rigid classification but so to arrange the subject matter as seems most likely to meet the requirements of the majority of readers.

2. Matter. — The bodies with which we are surrounded present an almost endless diversity of colour, appearance, and other characteristics. One property they however all possess in common, and that is the property of weight. All bodies are attracted by the earth, and any substance is said to be heavy because of the resistance which it offers to this earth-attraction or gravitation. Not only are solid bodies, such as iron and wood, possessed of weight, but so likewise are liquids, such as water and oil, and also gases, such as, for example, common air, or coal-gas. It is convenient to have one name for all bodies which possess weight, and for this purpose, in English, the term Matter is employed. Matter, then, is anything

THE TECHNOLOGY OF BREAH-MAKING.

which possesses weight (i.e., is acted on by gravitation), and exists in three distinct forms, namely, as solids, liquids, and gases.

3. Force. — The definition of matter just given would seem at first sight sufficiently comprehensive to embrace everything of which we can take cognisance, but yet a moment’s reflection shows the existence of other things beside matter. An illustration best demonstrates this fact — A hammer-head is known to consist of matter because it possesses weight ; but if with this hammer-head you give a series of blows to a small piece of nail -rod, you have given the nail-rod something which is not matter. The hammer-head is not lighter, nor is the nail-rod heavier — still the blows are something, as otherwise they could produce no effect. For one thing, the nail-rod will have been flattened and altered in shape ; further, and which is of far more present importance, it will have become hot to the touch. Again, to make use of another illustration, if a dry brick be carefully weighed and then made red-hot in a furnace, it will be found to weigh when hot precisely the same as it did when cold. Further, this brick, if allowed to become cold, imparts heat to surrounding objects, and nevertheless remains unaltered in weight. Here, then, is something very definite which a body can receive and again yield, and which is not matter. This something has, however, a very direct relation to matter ; in the first illustration the blows were struck by the moving hammer-head, which consists of matter in motion. The more rapid the motion, the more violent would be the blows ; in fact the force of the blow depends both on the quantity of matter and the rapidity of its motion. A number of considerations lead to the belief that the hot iron of the nail-rod and also the hot brick differ from the same substances in the cold state, in that their component particles are in a state of movement ; as these substances cool, the particles once more enter into a condition of comparative rest. This something beyond matter is closely associated with motion, and is termed force. Force is defined as that which is capable of setting matter in motion, or of altering the direction or velocity of matter already in motion. The motion of bodies may be divided into two classes : there is, first, that of the body as a whole, as in the case of the moving hammer-head ; second, the internal movements of the particles of a body, as when it becomes hot.

Elements of Heat.

4. Heat, its Nature and Effects. — Among generally observed facts with regard to heat, one of the first and most important is that it induces the sensation of warmth. According to the character and degree of this sensation, a body is said to be cold, warm, or hot. The conditions which produce this sensation of warmth also cause other well-marked changes in the physical condition of substances. The general effects of heat are to cause bodies as they get hot to expand in volume ; further, solids are reduced to the liquid state ; and, with still further increments of heat, liquids are converted into gases. The opposite series of changes occur as heat is abstracted from bodies. From the explanation of Force given in the preceding paragraph, it will be understood that these changes are not accompanied by any addition or diminution of weight. On the contrary. Heat is viewed as a form of Force, and is regarded as a mode or variety of internal motion of the particles of bodies — the hotter they are, the more violent and energetic is this motion.

5. Measurement of Heat : Temperature. — The earliest and most accessible measure to be applied to heat is that of the sensation of warmth before referred to, and according to whether a boiy to the touch is hot or cold, it is said to be of high or low temperature. Temperature is, in fact, the mea-

INTRODUCTORY.

sure of what is popularly termed “how hot a body is ; ” it will be seen on consideration that this depends on the power the body has of imparting heat to another body. Thus, if when the hand is thrust into water, the water is able to yield heat to the hand, it is said to be “hot,” while if it robs the hand of heat it is said to be “ cold.” The measure of this power is termed temperature, and is more exactly embodied in the following definition : — The temperature of a body is a measure of the intensity of its heat, and is further defined as the thermal state of a body considered with reference to its power of communicating heat to other bodies.

6. The Thermometer. — ^For scientific, and also for most technical, purposes, the sensations are not sufficiently accurate methods of measuring temperature ; accordingly temperature is usually measured by certain of the effects which heat produces : the most convenient for this purpose is the expansion of liquids with an elevation of temperature. For the general purposes of temperature measurement, the metal mercury is the most convenient substance. This liquid, enclosed in a suitable vessel, constitutes the temperature-measuring instrument termed a thermometer. In constructing a thermometer, a bulb is blown at one end of a glass tube of very narrow bore ; the bulb and tube are next filled with carefully purified mercury ; this is boiled, and thus all air and moisture are driven out of the tube ; the open end is then hermetically sealed by fusing the glass itself. At this stage the bulb and a portion of the tube are filled with mercury, the remainder of the tube being a vacuum, save for the presence of a minute quantity of mercury vapour. On heating the bulb of this

- instrument, the mercury expands and rises considerably in the stem. Throughout any body, or series of bodies in contact with each other, heat lias a tendency so to distribute itself that the whole series shall be at the same temperature ; consequently if the thermometer be placed in contact with the body whose temperature it is desired to measure, a redistribution of heat occurs, until the two are at the same temperature. That is to say, if the body be the hotter, it yields heat to the thermometer ; and if it be colder, it receives heat from the thermometer, until the temperature of both is the same. The two being in efficient contact, this stage is indicated by the mercury becoming stationary in the thermometer. Now the volume of mercury is constant for any one temperature ; therefore, to register temperature, it is only necessary to have further a scale, or series of graduations, attached to the stem of the instrument, by which the temperature may always be read.

7. The Pyrometer. — ^The ordinary mercury thermometer is not well adapted to the measurement of comparatively high temperatures, since the mercury boils at a temperature considerably below that of a dull red heat. In consequence other instruments have been devised for that purpose, to which the name of pyrometers has been given. The pyrometer may therefore be regarded as a high temperature thermometer. The pyrometers used for measuring the temperature of some types of bakers’ ovens, consist usually of a rod and casing constructed of materials which expand at different rates with an increase of temperature. The differential expansion actuates a needle moving in front of a dial plate.

8. Thermometric Scales. — Subject to certain precautions, the temperatures of melting ice and of steam in contact with boiling water are constant. The height at which the mercury stands when immersed in each of these is marked on most thermometers ; for the registration of other temperatures some system of graduation must be devised. The one most commonly employed in this country is that of Fahrenheit, while for scien-

THE TECHNOLOGY OF BREAD-MAKING.

tific purposes that of Celsius, or the Centigrade Scale, is almost universally adopted. Fahrenheit divided the distance between the melting and boiling points of his thermometer into 180 degrees ; degrees of the same value were also set off on either side of these limits. At 32 degiees below the melting point he fixed an arbitrary zero of temperature, from which he reckoned. On his thermometric scale, the melting point is 32°, while the boiling point is 32 + 180 = 212°. Degrees below the zero are reckoned as — (minus) degrees, thus —8° means 8 degrees below zero, or 40 degrees below the melting point ; degrees above 212 simply reckon upwards, 213, 214° F., etc.

The Centigrade Scale is much simpler, the melting point is taken as 0° or zero, and the boiling point as 100° ; temperatures below the melting point are reckoned as — degrees.

The conversion from one to the other of the Centigrade and Fahrenheit Scales may be easily performed.

180 Fahrenheit degrees = 100 Centigrade degrees.

0 — 5

1 ,, degree = ,, degree.

."> 5 5 5 5 ■ 1 5 5 5 5

There is this important difference between the two scales — Centigrade degrees count from the melting point, while Fahrenheit degrees are reckoned from 32 below the melting point.

30° C. = 30 X 5 = 54 Fahrenheit degrees.

Therefore 30° C. are equivalent to 54 Fahrenheit degrees above the melting point, but as the melting point is 32, that number must be added on to 54 ; the temperature Fahrenheit equal to 30° C. is 86°. By the reverse operation, Fahrenheit degrees are converted into degrees Centigrade. The following formulae represent the two operations : —

The following table gives the equivalent readings on the two thermometric scales for some of the most important temperatures —

-40°

-40°

F.

—

158°

F.

-17*7

? 9

9 9

80 ,,

=

9 9

’ 9

9 9

85 „

9 9

15-5

9 9

90 „

9 9

9 9 1

93-3 ,.

zzn

-—

9 9

95 ,,

9 9

9 9

100 „

—

9 9

26-6

9 9

9 9

150 „

9 9

1 200 „

9 9

—

232*2

=

9 9

37-7

9 9

9 9

250 !!

9 9

9 5

260 „

=

9 9

9 9

9 9

287*7 „

9 9

9 9

300 „

—

9 9

9 9

316*6 ,,

9 '

9 9

9 9

! 350 „

9 9

9 9

1 400 „

9 J

9. Quantity of Heat. — Temperature is not a measure of quantity of heat, for a thermometer would indicate the same temperature both in a vessel containing a pint, and one containing a gallon of boiling w^ater, although it is evident that one must contain eight times as much heat as the other ; further, to raise the gallon of water to the boiling point, eight ^mes the amount of heat necessary to similarly raise the pint is required. This leads to the mode of measuring and registering quantity of heat. Quantity of heat is measured by the amount necessary to raise a certain weight of some body from one to another fixed temperature. The amount of heat necessary to raise 1 gram of water from 0° to 1° C. is termed a Unit of Heat. For the phrase Unit of Heat, a distinctive term, “ Calorie ” is now frequently employed From this it follows that to raise 2 grams of water from 0 to 1 C. will require 2 Units of heat, or 2 H.U., or 2 Calories. Befreezing and the boiling points, ap'proximately the same amount

01 heat IS necessary to raise 1 gram of water through any 1 degree of temperature, so that to raise 1 gram through 2 degrees will require approximately

2 H.U. For practically all purposes, it may be taken that the weight of water in grams X degrees of temperature through which it must be raised — the number of H.U. required.

10. Specific Heat.— The quantity of heat necessary to raise the same V eight of different substances through 1 degree of temperature varies very

considerably. The quantity of heat necessary to raise) 1 gram of any substance through 1 degree of temperature is termed its SpeciBc Heat. Prom this definition it follows that the specific heat of water at 0° C is I'OO or unity. The following table gives the specific heat of various substances’;—

Substance.

Water Alcohol

Glass Iron . .

Copper Mercury

Specific Heat.

1-00000

0-61500

0-19768

0-11379

0-09391

0-03332

If equal weights of water at different temperatures are mixed together the result is a mixture having a temperature the mean of the two • thus a gallon of water at 20° C. mixed with a gaUon at 50° C. will produce a mixture at the temperature of 35° C. But if equal weights of two substances of different specific heats be thus mixed, the temperature of the mixture of the two will not be a mean of those of the substances, but will be nearer that of the substance having the higher specific heat. The most important mixture with which the baker has to do is that of flour with water, as the temperature of the resultant dough is a matter of vital concern to him The results are complicated by the presence of other ingredients, as salt and yeast, and also in practice by loss of heat through absorption by the surroundings of the dough, and heat generated by chemical action among the ingredients. The following are the results of laboratory experiments made by mixing together flour and water only, and carefully taking the temperatures, but not allowing for loss of heat absorbed bv containing vessels. ^ of flour at

Specific Heat.

500 „

water at

0-53 flour at

500 „

water at

0-42

500 „

flour at

500 „

water at

0-40

I heats are calculated from the above experiments in the

lollowmg manner : in the first experiment 500 grams of water have fallen from H5 to 118°, that is 27°, during which they must have afforded 500 x ~ 13,500 H.U. At the same time 500 grams of flour have been raised

THE TECHNOLOGY OF BREAD-MAKING.

from 67° to 118°, that is through 51°, which is equal to 500 x 51 = 25,500 grams through 1°, and to do this 13,500 H.U. have been utilised ; then to raise 1 gram through 1° there has been taken

13.500

25.500

= 0*53

H.U.

therefore 0*53 is the specific heat of flour as derived from this experiment.

A number of observations have also been [made on the temperatures of mixtures made in the bakehouse on the large scale for manufacturing purposes. The doughs were machine-mixed, and no allowance is made for the salt and compressed yeast, quantities of which were the same in all cases. The quantities, temperatures, and calculated specific heats are given in the following table : —

Water.

Flour.

Dough.

Flour.

Specific

Heat.

0-39

Quarts.

Lbs. Temp.

132-5 95°

Lbs.

Temp.

52-5°

Temp.

79-0°

127-5

90°

50-0°

77-0°

0-30

127-5

90°

50-0°

77-0°

0-30

132-5

98°

53-0°

79-0°

0-45

132-5

89°

53-0°

76-0°

0-36

132-5

89°

53-0°

76-0°

0-36

The whole of these figures, it must be remembered, are those obtained in experiments made under conditions such as hold in the bakehouse, and represent rather the result of actual working, than theoretic specific heats with all disturbing causes eliminated. In the case of the mixtures made at the higher temperatures, there is naturally a greater loss of heat, and this causes an increase in the corresponding apparent specific heats. In consequence of this, the No. 1 Laboratory Experiment gives a remarkably high figure ; but the whole of the others lie fairly closely together. Comparing those above given with a large number of observations on the manufacturing scale since made, practically all the specific heat results range between 0‘36 and 0*45, with a mean of 0‘40, to which the majority approach most closely. Taking 0*40 as the working s]3ecific heat of flour, 1 unit by weight of water in falling through 1° raises 2-5 units by weight of flour through the same increment of temperature.

11. Sources of Heat. — ^Directly or indirectly all available terrestrial heat is practically derived from the sun : its immediate source, however, for manufacturing operations is the combustion of different kinds of fuel ; these give out different amounts of heat according to their composition. Tlie following table gives the number of heat units evolved by the combustion of one gram of each substance in oxygen : —

Heat Developed during Combustion.

Substance.

Formula

Heat Units.

H,

34,462

Carbon . .

C

8,080

Carbon Monoxide

CO

2,634

Marsh Gas

CH4

13,063

Olefiant Gas

C2H4

11,942

Alcohol . . . . . .

C2H5HO

6,909

Welsh Chal

about

8,241

Newcastle Coal

8,220 '

D( rbysliire Coal

7,773

Coke

7,000

Wood (dried in air)

. .

3,547

INTRODUCTORY.

12. Expansion by Heat. — It has already been mentioned that in most cases bodies expand under the influence of heat. Solids expand the least, and at a definite rate for each particular solid ; liquids have a higher rate of expansion, each still having its own special rate ; while gases expand at a far higher rate than either liquids or solids. The following table gives what are termed the

Coefficients of Linear Expansions for I° between 0° and 100° 0. Glass.. .. 0*000008613 Brass.. .. 0*000018782

Tliese figures mean that each of these substances expands at the rate expressed by its own coefficient : thus 1 foot of glass at 0° C. becomes 1*000008613 foot long at 1° C., and so for each degree rise in temperature. When a body is heated, its whole three dimensions of course increase, and the coefficients of cubical expansion of solids for practical purposes, may be taken as three times their coefficients of linear expansion.

The apparent expansion of liquids is not so great as the real, because the vessels in which they are contained also expand. The following table gives the

Total Apparent Expansions of Liquids between 0° and 100° C. Mercury . . . . 0*01543 Fixed Oils . . . . 0*08

Distilled Water . . 0*0466 Alcohol . . . . 0*116

The coefficient of apparent expansion for 1° C. is obtained by dividing these numbers by 100, thus that for mercury is 0*0001543. Mercury expands at a practically constant rate from 36° to 100° C. ; water, however, contracts in rising from 0° to 4°, and then expands from 4° to 100° C.

13. Expansion and Contraction of Gases. — There are certain reasons V hich lead us to suppose that at a temperature of — 273° C. bodies would be entirely devoid of heat. This point — 273° C. is therefore often termed the absolute zero of temperature ; and temperature reckoned therefrom is termed “ absolute temperature.” The absolute temperature of a body is its temperature in degrees C. + 273. All gases expand with increase, and contract with diminution, of temperature. The amount of expansion and contraction is the same for all gases between the same limits of temperature, provided the temperature is considerably higher than that at which they condense to liquids. The volume of all gases is directly proportional to their absolute temperature. Because of this variation with temperature it is necessary to fix a temperature which shall be considered as a standard in expressing the volume of gas : 0° C. is commonly adopted for this purpose.

Knowing the volume of a gas at any one temperature, its volume at any other may be easily calculated ; thus, a vessel was found to contain 750 c.c. of air at 15° C. ; it is required to find its volume at the standard temperature.

15° C. -f 273 = 288° Absolute Temperature.

As 288 : 273 : : 750 ; 711 c.c. of gas at standard temperature.

14. Relation of Pressure and Volume of Gases. — It is convenient here to note that the volume of a gas is also affected by the pressure to which it is subjected : this variation is governed by what is called Boyle and Marriotte’s Law — ^The volume of any gas is inversely proportional to the

THE TECHNOLOGY OF BREAD-MAKING.

pressure to which it is subjected. The most important variations of pressure to which gases are liable are those resulting from the changes in pressure of the atmosphere. The height of the mercury column of the barometer is a direct measure of the pressure of the atmosphere, therefore that pressure is commonly expressed in the number of millimetres (m.m.) which that column is high. For purposes of comparison it is also necessary to reduce all pressures to one standard ; that selected is an atmospheric pressure which causes the barometer to stand at 760 millimetres.

The temperature and pressure quoted as standards for gas measurement 0° C. and 760 m.m. are often termed normal temperature and pressure ; for this expression the abbreviation, “ N. T. P.” is frequently used.

The laws governing the relation between the volume and temperature and pressure of gases must not be regarded as absolutely exact, since they are subject to certain small but well-marked departures. These variations, however, have no direct bearing on the present subject.

15. Transmission of Heat. — ^It is well known that when one part of a body or place is heated, the other parts also become hot more or less quickly. Some explanation of how such transmission is effected must now be given.

There are three methods by which heat can be transmitted from one point to another, which are termed respectively Convection, Conduction, and Radiation.

16. Convection. — ^As the word convection implies, a part or mass is heated by the heated matter being conveyed from one part to another. This kind of heating can only occur in liquids or gases where the particles of matter can move freely. One of the best illustrations of convection is the heating of an ordinary vessel of water by the placing of a fire underneath ; the layer of water at the bottom first gets hot, and consequently expands and becomes of lower specific gravity. As a result of being lighter, it therefore rises to the surface, and its place is taken by other water which is colder and denser. This in its turn is heated and rises ; continuous currents of warm water ascend through the liquid, and colder water descends to take its place. In this way the whole mass is gradually made hot. The heating of the water in a supply cistern on the top of a building by currents through flow and return pipes from a small boiler in the basement is due to convection. So, too, the ventilation of a building is naturally caused in the same way — heated air ascends and makes its way through exits at the highest point, while cold air enters through the joints of doors and windows or apertures specially provided for the purpose. Among other illustrations may be mentioned the warming of a building or room by hot-water pipes running close to the floor. The air is thereby heated and ascends ; the cooler air falls and takes its place. Conversely, a mass of water or air is best cooled by the application of cold at the upper surface. Thus, given a vessel of hot water and a coil of pipes at the surface, through which cold water is passing, the cold water lowers the temperature of the upper layer in the vessel ; this consequently descends and its place is taken by hotter water. In this way a series of currents is set up whereby the whole mass of water is uniformly cooled. It will be seen that convection is a mode of distributing heat through a mass of either liquid or gas by means of moving currents, such currents being usually produced by differences in density due to expansion caused by the source of heat itself.

17. Conduction. — ^Instances are well known in which the application of heat to any one point of a solid causes the whole mass to become hot. Thus, if the end of a bar of iron be placed in the fire, the other end gradu-

INTRODUCTORY.

ally increases in temperature. This cannot be due to convection, but is due to the heating effect which the hot particles of the body have on the contiguous particles. In these cases the heat is said to be transmitted by conduction. Conduction is that method of transmitting heat in which the heat passes from the hotter particles of a body to the colder ones lying in contact with them, and so throughout the whole body.