12. STRUCTURE OF WHEAT GRAIN.--In its natural state, wheat contains all the food substances required for the nourishment of the human body in nearly the proper proportions, and in addition it has in its composition sufficient cellulose to give it considerable bulk. It has been estimated that the average composition of this grain is as follows:
| PER CENT. | |
| Protein | 11.9 |
| Fat | 2.1 |
| Carbohydrates | 71.9 |
| Mineral salts | 1.8 |
| Water | .5 |
| Cellulose | 1.8 |
| Total | 100.0 |
So that the composition of wheat and the making of wheat flour may be more clearly understood, it will be well to observe the structure of a grain, or kernel, of wheat, which is shown greatly enlarged in Fig. 1. At a is shown the germ of the young plant, which remains undeveloped until the grain is planted. This part contains practically all the fat found in the grain, some starch, and a small quantity of protein. At b is shown the inside of the kernel, or the endosperm, as it is called, which is composed of starch granules interlaced with protein and mineral salts. Surrounding these, as at c, is a layer of coarse cells that contain mineral matter and protein, and between these cells and the outer husk, as at d, e, f, and g, are layers of bran, which are composed of cellulose and contain mineral salts and small quantities of starch and protein. Enveloping the entire kernel is a husk, or bran covering, h. This forms a protection to the rest of the grain, but it cannot be used as food, because it is composed almost entirely of cellulose, which is practically indigestible. The center of the grain, or the heart, is the softest part and consists of cells filled with starch. From this soft center the contents of the grain gradually grow harder toward the outside, the harder part and that containing the most gluten occurring next to the bran covering.
13. MILLING OF WHEAT FLOUR.--Great advances have been made in the production of flour from wheat, and these are very good evidence of man's progress in the way of invention. The earliest method consisted in crushing the grain by hand between two stones, and from this crude device came the mortar and pestle. A little later millstones in the form of thick, heavy disks were brought into use for grinding grain. Two of these stones were placed so that their surfaces came together, the lower one being stationary and the upper one made to revolve. Early grinding apparatus of this kind was turned by human power, but this kind of power was first displaced by domestic animals and later by wind and water. Out of this arrangement, which is still used to some extent in small mills, has grown the present-day complicated machinery of the roller process, by which any part of the grain may be included or rejected.
14. In the roller process, the grain is crushed between metal rolls instead of being ground between stones. It is first screened in order to separate all foreign matter from it, and then stored in bins. When it is taken from these receptacles, it is put through another cleaning process, called scouring, or it is thoroughly washed and dried in order to loosen the dirt that clings to it and to free it entirely from dust, lint, etc. As soon as it is completely cleansed, it is softened by heat and moisture and then passed through a set of corrugated rollers, which are adjustable as are the rubber rollers of a clothes wringer and which flatten and break the grains. After this first crushing, some of the bran is sifted out, while the main portion of the grain is put through another set of rollers and crushed more finely. During the milling, these processes of crushing the grain and removing the bran are repeated from six to nine times, each pair of rollers being set somewhat closer than the pair before, until the grain is pulverized. After the grain has been thus reduced to a powder, it is passed through bolting cloth, which acts as a very fine sieve and separates from it any foreign material that may remain. The result is a very fine, white flour.
15. GRAHAM FLOUR.--Sometimes the entire grain, including the bran, germ, etc., is ground fine enough merely for baking purposes and is used as flour in this form. Such flour is called graham flour. It contains all the nutriment, mineral matter, and cellulose of the original grain, and is therefore considered valuable as food. However, the objection to this kind of flour is that its keeping quality is not so good as that of the kinds from which the germ has been removed, because the fat contained in the germ is liable to become rancid.
16. WHOLE-WHEAT FLOUR.--The best grades of fine white flour make bread of excellent quality, but such bread is not so nutritious as that made from whole-wheat flour. In the making of this kind of flour, some of the choicest varieties of wheat are first moistened in order to soften the woody fiber of the bran and are then sifted until the outer husk of the grain is removed. After this treatment, the grains are dried and then pulverized into various grades of so-called whole-wheat flour. The name whole-wheat flour is misleading, because it implies that all of the grain is used; whereas, since several of the outer layers of bran and the germ are removed in its production, whole-wheat flour is merely flour in which practically all the gluten and the starch are retained. Because this variety is not sifted as are the white flours, it is not so fine as they are; but it is not so coarse as graham flour, nor is bread made from it so dark in color. Both graham and whole-wheat flours produce a more wholesome bread than any of the varieties of white flour, because they contain more of the nutritive elements and mineral salts, which are necessary in the diet. The bran that is retained in them is not used by the body as food, but it adds bulk to the diet and assists in carrying on the normal functions of the digestive tract.
17. SELECTION OF FLOUR.--If a large quantity of flour must be bought at one time, as, for instance, enough to last through an entire season, it is advisable to test it carefully before the purchase is made, so as to avoid the danger of getting a poor grade. As a rule, however, housewives are obliged to purchase only a small quantity at a time. In such cases, it will not be necessary to test the flour before purchasing it, provided a standard make is selected. Very often, too, a housewife in a small family finds it inconvenient to keep on hand a supply of both bread flour and pastry flour. In such an event, a blend flour, which, as has been mentioned, is a mixture of flour made from spring and winter wheat that will do for all purposes, is the kind to purchase. While such flour is not ideal for either bread or pastry, it serves the purpose of both very well.
18. QUALITY OF FLOUR.--Flour is put on the market in various grades, and is named according to its quality. The highest grade, or best quality, is called high-grade patent; the next grade, bakers'; and the next, second-grade patent. The lowest grade, or poorest quality, is called red dog. This grade is seldom sold for food purposes, but it is used considerably for the making of paste.