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 121 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, 122 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 123 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
or offal     Protein
per cent.     Phosphoric acid
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     2·5

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 12? per cent. in the hard foreign wheats as compared with 10 per cent. in home grown wheats. Thus the presence of a larger 124 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 125 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 126 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
which bread
was made     Percentage of
the grain
contained in
the flour     Amount of protein digested
per 100 parts eaten
American
experiments     Cambridge
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 127 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 128 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 whit............