22 



BULLETIN" 557, IT. S. DEPARTMENT OF AGRICULTURE. 



those in loaf volume, although the differences are not so marked. 

 The average variation in texture between the several classes is 

 largely an indication of differences arising from the number of 

 cavities in the loaf, which is clearly related to the thickness of the 

 walls of these cavities and consequently to the character of the 

 crumb. "When the walls of the cavities are very thin the bread is 

 elastic and yielding to the touch, does not crumble easily when cut 

 into thin slices, but is nevertheless tender and free from toughness. 

 Bread with thick cell walls may be brittle, or very crumbly and 

 harsh to the touch when cold, or rubbery and lacking tenderness. 

 Soft wheats tend toward the former, while the very hard wheats of 

 poor quality tend toward the latter condition. 



RELATION BETWEEN CRUDE PROTEIN IN WHEAT AND THE 

 STRENGTH OF FLOUR. 



The strength of wheat flour apparently bears a very intricate rela- 

 tion to its composition. The physical properties of the proteins of 



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Fig. 18. — Diagram showing the variations in crude protein of four classes of wheat. 

 Samples from the crops of 1908 to 1913, inclusive. 



the wheat kernel have long been known to be chiefly responsible for 

 those characters of wheat flour which differentiate it from the flour of 

 other cereals with regard to its ability to retain the gas produced by 

 yeast fermentation. 



Figure 18 shows graphically the ranges and averages of the crude 

 protein content of soft red winter, durum, hard red spring, and hard 

 red winter wheats. With soft red winter wheat the extreme range is 

 from between 7 and 8 to between 14" and 15 per cent, nearly 90 per 

 . cent of the samples, however, falling between 9 and 12 per cent, the 

 average being 10.6 per cent. This average is 1.5 per cent lower than 

 the next highest, which is hard winter wheat. The crude protein 

 content of durum wheat averages 14.3 per cent and the extreme range 

 is from 9 and 10 to between 18 and 19 per cent, with about 88 per cent 

 of the samples falling between 11 and IT per cent. 



Figure 19 shows the relation between the total crude protein of 

 wheat and the strength of the flour within the three classes of common 

 wheat under discussion. 



