24 



BULLETIN 557, U. S. DEPARTMENT OF AGRICULTURE. 



tion should also be made of durum wheat, which on the average has 

 the highest crude protein of any wheat, but which is of only medium 

 strength. 



The wide difference between durum and common wheat in the rela- 

 tion between these factors has been mentioned. Some differences in 

 the relation of crude protein to loaf volume or expansion are also 

 observed with other classes of wheat. For a given percentage of 

 protein the loaf volume is greater for hard red spring wheat than 

 for either hard or soft red winter wheat and is greater for hard 

 winter than for soft winter wheat. This is illustrated in figure 19. 



PROTEIN CONTENT OF WHEAT AND FLOUR. 



Since in baking flour is used rather than the wheat itself, it is of 

 interest to note the relation between the protein content of flour and 

 that of the wheat from which it is made. The data in Table V show 

 the general variations to be expected, and it is evident that the pro- 

 tein content of the flour, as a rule, is considerably lower than that of 

 the wheat, though in a small percentage of cases it appears to be 

 slightly higher. 



Table V. — Relationship between the crude-protein content of wheat and that 

 of straight flour produced from hard and soft red winter and hard red spring 

 wheat of the crops from 1909 to 1913, inclusive. 



Crude protein in straight flour. 



Proportion of samples falling into various ranges 

 protein content of wheat (per cent). 



in crude- 



8 to 

 8.9 



9 to 

 9.9 



10 to 

 10.9 



11 to 



11.9 



12 to 

 12.9 



| 

 13 to 14 to 

 13.9 14.9 



15 to 

 15.9 



16 to 

 16.9 



17 to 

 17.9 



Range (per cent): 



17 to 17.9 



















25 



16 to 16.9 

















50 



15tol5.9. . 

















67 



14 to 14.9. 











1.5 

 12.8 

 66.2 

 17.3 



2.3 



4.3 



52.9 



35.6 



5.7 



1.4 



55. 5 



38.9 



5.6 



33 25 



13 to 13.9 















12 to 12.9. 







0.5 

 2.5 



40 

 52 



5.6 | 16.2 

 21 | 62. 1 

 60. 1 ' 20. 7 

 12.4 





11 to 11.9 









10tol0.9. . 



4.2 



44.7 

 46.9 

 4.2 







9 to 9.9 











8 1 o 8.9 



31.7 

 68.3 



.9 











7 to 7.9 























19 47 



203 224 203 



133 70 



36 



3 4 























Cases where the protein content of flour is higher than that of the 

 wheat are evidently abnormal and are explained by the differences in 

 the moisture content of the wheat and of the flour. A sample of 

 wheat of unusually high moisture content might appear to have a low 

 percentage of protein, while the flour having a moisture content sev- 

 eral per cent lower might appear higher. This seeming inconsistency 

 could be eliminated by calculating constituents to a dry basis, but 

 this hardly seemed desirable, as it makes the interpretation of results 

 more complex from a commercial standpoint. 



