ilz ANNUAL REPORT OF THE Off. Doc. 



Richardson* made 208 pai'tial analyses of winter wheats from the 

 Atlantic, Gulf and Middle States and of 33 samples of spring wheats 

 from Minnesota, Dakota and Manitoba; the respective protein aver- 

 ages are 11.47 and 14.07 per cent. These data indicate an average of 

 13 to 13.5 per cent, of protein for spring wheats, an amount from one 

 to two per cent, greater than that in winter wheats. 



The structure of the wheat grain divides it into essentially four 

 principal parts: 1. The epidermis or skin, including the hairs at 

 the tip of the grain and three thin outer layers, weighing collect- 

 ively about 3 pounds in 100 pounds of grain. 2. The color layer, 

 composed of small cells containing two pigments, a yellowish' and a 

 red, according to whose relative predominance the color of the grain 

 is "white," "amber'' or "red." This forms 2 pounds in 100 pounds of 

 grain. 3. The germ or embryo, located at the lower part of the grain 

 and connected with a thin layer of tissue entirely enveloping (4) the 

 endosperm- or inner portion of the grain. 



The outer layers are almost wholly composed of woody tissue. 

 The germ is chiefly composed, on the other hand, of protein, oil and 

 certain ash materials. The endosperm is not at all uniform in com- 

 position. At the center it is white and powdery, and is composed 

 chiefly of starch enclosed in large, thin-walled cells. But toward 

 the exterior of the mas® of endosperm, the starch diminishes in 

 proportion, and albuminoids, fats and ash become more abundant. 

 The laxative materials of the endosperm, probably albuminoid in 

 nature, also increase, relative to the other albuminoids, as the ex- 

 terior is approached, and among the ash constituents, the lime grows 

 relatively less, the magnesia more abundant. 



The process of milling has for its object the powdering of the 

 grain and the removal of the less desirable portions. The germ is 

 removed because flours retaining it, tend, on standing, to darken 

 and become ill-flavored. The outer layers are removed as bran. 

 This is not, however, composed wholly of the epidermis and color 

 layers, but also includes a large proportion of the endosperm, more 

 especially of the outer, albuminoid layers of it. When separately 

 prepared, these outer layers constitute the middlings, a dark flour 

 making a "runny" dough. In general, the milling process commonly 

 yields but 70 to 75 per cent, of flour and 25 to 30 per cent, of bran 

 and middlings, including the germ, as its separation from other by- 

 products is not common in many mills. 



The character and proportion of the several milling products 

 varies, of course, both with the character of the grain and the de- 

 tailed method of milling. There are three principal methods of 

 milling, two stone-milling processes and one roller process. For- 

 merly, the flour was thoroughly ground by a single run through close- 



•Bulletlns 4 and 9, Chemical Division, U. S. Dept. of Agrlc. 



