crude fiber than the grain. The highest grades consist of approximately pure endosperm, but since in producing these highest grades it is necessary to reject practically all of those portions of the endosperm that remain attached to the embryo and to the aleurone layer, it is customary in the roller process of milling to make several grades of flour with varying admixtures of portions foreign to the endosperm, in order to increase the total percentage of the flour. The superiority of the modern methods of milling lies largely in the exactness with which the various products of the wheat grain can be sorted. The almost complete elimination of crude fiber in the patent flour is probably one of the most important factors in affecting its commercial and breadmaking value. Another rather important factor is the fineness of the particles of flour. While flour seems like an impal

pable powder, there is in reality considerable variation in the size of the particles, as may be readily determined by passing flour through sieves of proper dimensions. Microscopic examination will show that some particles are spherical, while others are angular. Flour from hard wheat is generally larger and more angular than that from soft wheat. The character of the milling has, of course, the greatest effect upon the granulation of the flour. The most desirable condition for breadmaking probably exists when the flour is of medium granulation, with a mixture of medium and smaller sized particles, as the capacity of the flour to absorb water is thus increased.1

The quantity and quality of the flour therefore depend upon the character of the wheat grain both physically and chemically, upon its condition at the time of milling, upon the mill and upon the skill of the miller. Usually seventy to seventy-two per cent of the grain is made into flour, although variations ranging from sixty-five to eighty per cent have been reported for different varieties of wheat milled by the roller process. Where

1 The Northwestern Miller, Christmas, 1900, p. 20.

U. S Dept. of Agr., Div. of Chem. Bul. 4 (1884), p. 60.

millers do custom milling for an eighth toll, it is customary to give thirty-six to thirty-seven pounds of flour and twelve to fourteen pounds of mill feed for each bushel. While wide variations may occur on account of differences in the process of milling and mixing, ordinarily about one-half the by-product is bran, and the other half shorts and middlings.

The larger the endosperm and the smaller the embryo and aleurone layer, the larger the percentage of flour obtained. The evidence seems conclusive that the embryo and aleurone layer are considerably nigher in ash, and especially in phosphoric acid, nitrogenous compounds and fat, than the endosperm, and that the composition of wheat may vary on account of the proportion of these to endosperm without any variation in the composition of the endosperm. There is, therefore, no necessary relation between the composition of the wheat grain and the composition of the flour therefrom. In general, however, grains with high percentage of nitrogenous compounds produce flour with high percentage of these compounds and with high gluten content. (69)

173. Grades of Flour.-The expert miller determines the quality of the flour largely by feel and color. Great expertness is acquired in judging of the granulations by the feel, which depends both on the size of the flour particles and their form. The quality of the flour also depends upon the per cent and quality of the gluten. (70) The quality of the gluten may be determined by the "baker's sponge test" by which the volume of dough per unit of gluten as well as the time required to obtain the maximum rise is determined. (204)

Many trade names are given to different grades of flour by manufacturers. Dealers have sought to obtain uniformity of grading by a system of inspection similar to that employed for whole wheat and other grains. As a guide for the inspector, a series of standards is prepared and renewed from time to time as required. The classification differs in different cities.

In

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

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

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).1 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

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.