======================================================== | Per Cent Water | 12.00 | { Potash } | { Soda } | { Lime } | Ash { Magnesia } | 2.25 { Phosphoric anhydrid} | { Sulphuric anhydrid } | { Other substances } | | { Albumin 0.4} | { Globulin 0.9} | Protein { Gliadin 6.0} | 13.00 { Glutenin 5.3} | { Other proteids 0.4} | Other nitrogenous bodies, as amids, lecethin | 0.25 Crude fat, ether extract | 2.25 Cellulose | 2.25 Starch | 66.00 Sucrose, dextrose, soluble carbohydrates, etc.| 2.00 =======================================================
154. Roller Process of Flour Milling.--Flours vary in composition, food value, and bread-making qualities with the character of the wheat and the process of milling employed. Prior to 1870 practically all wheat flour was prepared by grinding the wheat between millstones; but with the introduction of the roller process, steel rolls were substituted for millstones.[60] By the former process a smaller amount of flour was secured from the wheat, but with the present improved systems about 75 per cent of the weight of the grain is recovered as merchantable flour and 25 per cent as wheat offals, bran, and shorts[61].
[Illustration: FIG. 38.--GRANULAR WHEAT FLOUR PARTICLES.]
The wheat is first screened and cleaned, then passed on to the corrugated rolls, or the first break, where it is partially flattened and slightly crushed and a small amount of flour, known as the break flour, is separated by means of sieves, while the main portion is conveyed through elevators to the second break, where the kernels are more completely flattened and the granular flour particles are partially separated from the bran. The material passes over several pairs of rolls or breaks, each succeeding pair being set a little nearer together. This is called the gradual reduction process, because the wheat is not made into flour in one operation. More complete removal of the bran and other impurities from the middlings is effected by means of sieves, aspirators, and other devices, and the purified middlings are then passed on to smooth rolls, where the granulation is completed. The flour finally passes through silk bolting cloths, containing upwards of 12,000 meshes per square inch. The dust and fine débris particles are removed at various points in the process. The granulation of the middlings is done after the impurities are removed, the object being first to separate as perfectly as possible the middlings from the branny portions of the kernel. If the wheat were first ground into a fine meal, it would be impossible to secure complete separation of the flour from the offal portions of the kernel.
