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St. Louis the grades are Patent, Extra Fancy, Fancy, Choice and Family, in which the first named indicates the whitest and highest quality, and the last the darkest and lowest grade.1

174. Graham and Entire Wheat Flour.-Graham flour is unbolted wheat meal, while whole wheat or entire wheat flour is wheat meal from which the coarsest of the bran has been removed. It contains, therefore, the embryo and perhaps some portion of the aleurone layer.

The following table gives the composition of a hard Scotch fife wheat, and of graham flour, entire wheat flour and of straight grade patent white flour made therefrom:2

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When made into bread it was found that the white flour made the lightest bread (the largest loaf) and that the graham flour made the smallest loaf. Expressing the digestibility of the bread when fed to men in terms of available energy, it was found that 90.1 per cent of the white bread, 85.5 per cent of the entire wheat bread and 80.7 per cent of the graham bread was digested. The greater digestibility of the white flour was, in part, attributed to its greater fineness. The result of this and other experiments indicates that while bread from graham and entire wheat flour is a perfectly healthful and often desirable article of diet, bread from white flour produces the largest amount of

1 Ark. Bul. 42, p. 66.

2 Minn. Bul. 74, p. 157.

energy per unit of flour and is probably to be preferred as the main diet for the average person. The digestibility of bread from different grades of patent flour was quite similar.

175. Amount of Bread from Flour.-The value of flour depends upon the amount and quality of bread produced. (172) The amount of bread does not, however, depend upon the flour alone but also upon the conditions of baking, chief of which are the percentage of water used in the dough, the size of the loaves, the temperature of the ovens and the length of time of baking. Richardson reports that by differences in these factors the amount of bread may be varied as much as fifteen pounds per 100 pounds of flour. For different flours handled as nearly alike as may be, he obtained variations ranging from 129 pounds to 140 pounds of cold bread for each 100 pounds of flour, and he concludes that the yield of bread is dependent on physical conditions of breadmaking and not to a large extent upon the chemical composition of the wheat (flour). It was a fact, however, that the flour with the least per cent of nitrogen produced the smallest per cent of bread and the flour with the largest per cent of nitrogen produced the largest per cent of bread. As the percentage of flour in wheat is about seventy-two, each pound of wheat produces about a pound of bread.

176. Milling Machinery.—There are three types of machinery for producing flour which may be represented as follows:

I. The mortar and pestle, which is the primitive method, in which the force employed is principally that of impact.

2. Burr stones, which was the universal method of milling wheat in the United States until 1878, in which the wheat is cut and crushed.

3.

The roller process, which has made large mills possible, in which the wheat, and subsequently its several parts, pass through a series of graduated hardened steel rollers and in which

1 U. S. Dept. of Agr., Bu. of Chem. Bul. 4, pp. 60-62.

the material is mashed, rather than torn as in the burr stones. There were in the United States in 1900 about two and one-half as many pairs of rolls as runs of stone.

The separation of the different portions of the grain is accomplished partly by gravity and partly by bolting cloth of different sized meshes. The endosperm breaks up into spherical or cubical particles, while the other portions are more or less flattened, forming comparatively larger dimensions and having a less specific gravity.

177. The Purifier.-Formerly, and by what is now known as the old process of milling, wheat was merely ground as finely as possible and then bolted. By the introduction of the middlings purifier two steps have been added to the process, viz., puri

The middlings purifier, which has greatly influenced

the wheat industry.

fying and regrinding. The details of this "new" process are elaborate and complicated but the principles involved are quite simple. The thoroughly cleaned wheat, whether rolls or burrs are used, is first ground, or rather granulated coarsely, resulting in three products: flour of a low grade, middlings and bran. The middlings are now put through the purifier in order to extract dirt, bran and fuzz. They are then ground by a more or less gradual process, depending upon the construction of the mill, and finally bolted. It is from these middlings thus purified that the highest grade (so-called patent) of flour is made.

The introduction of the purifier in 1870 revolutionized the process of milling, and made the use of the hard spring wheats of the Northwest of the highest value, while formerly they were of the least value for the production of high grade flour.

178. The By-products of Wheat consist of the outer coats, the aleurone layer, the embryo, and such portions of the endosperm as cannot, by the common process of milling, be removed from the aleurone layer. There are a number of grades of these by-products, depending principally upon the relative proportion of outer coats to endosperm. The common grades are bran, shorts and middlings, while a low grade of flour known as "red dog" or "dark feeding flour" is sometimes sold for feeding purposes. Bran and shorts are essentially the same, except that in the process of milling the outer coats in the latter are more thoroughly pulverized; while the middlings contain a larger portion of the endosperm, and are therefore more starchy and dense than bran or even shorts. In the bran the outer coats are in large flakes, with portions of the aleurone layer and endosperm attached, thus making a light, bulky product. While the embryo itself constitutes a much smaller proportion, in the process of milling about eight per cent of the grain is removed as embryo. (64) Care is taken to remove these embryos, because their introduction into the flour injures its keeping qualities, and its nitrogenous compounds are not suitable for breadmaking purposes. On account of their high nitrogen, phosphorus and fat content, they are a valuable addition to the by-products. They are sometimes found in the bran and sometimes in the middlings. As in the process of milling they are separated from the rest of the products, it is optional with the miller where they are put. The yellowish flattened embryos are readily recognized in the mill products.

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179. Composition of By-products. The analyses that have been compiled show very great variations in every constituent in different samples of bran, shorts and middlings. Taking them as a class, the ash has been found to vary from 1.4 to 7.8 per cent; the protein from 10.1 to 20.0 per cent; the crude

1 The Chemistry of Plant and Animal Life, p. 307.

U. S. Dept. of Agr., Office of Expt. Sta. Bul. 11.

fiber from 1.3 to 15.5 per cent; nitrogen-free extract from 45.5 to 70.9 per cent; and fat from 1.5 to 7.0 per cent. The following table shows the average composition:

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High protein content may be accompanied with high content of crude fiber and low content of starch due to exhaustive milling, and equal protein content may result in two samples of bran unequally milled because of differences in the protein content of the wheat used.

The total phosphorus in wheat bran has been found by the New York (Geneva) Station to be 1.22 per cent, as compared with 0.7 per cent in malt sprouts and 0.4 in oats. It is also more soluble, eighty-seven per cent being soluble in water, as compared with eighty-one per cent in malt sprouts and fifty per cent in oats. Practically all of the soluble phosphorus of wheat bran is of an organic nature.'

180. Food Value of By-products. Within the memory of many persons now living, the bran spout of grist mills emptied its contents into the river. The by-products of wheat are now among the most highly prized stock foods for all classes of domestic animals. While its value is undoubted, the digestibility of bran is not much greater than that of hay of good quality. The esteem in which it is held sometimes causes it to be an expensive food compared with others that are available. 1 N. Y. (Geneva) Bul. 250 (1904), p. 169.

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