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 
13.9 
14 to 
14.9 
15 to 
15.9 
16 to 
16.9 
I7t0 
17.9 
Range (percent): 
17 to 17 9 
| 
25 
16 to 16 9 
50 
15 to 15.9. . 
:::::::::::: 
67 
33 
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 
25 
13 to 13 9 
"'6.' 5' 
2.5 
40 
52 
5 
' 
5.6 i 16.2 
21 62. 1 
60. 1 1 20. 7 
12.4 
12 to 12 9 
11 to 11.9. 
10 to 10 9 
4.2 
44.7 
46.9 
4.2 
9 to9 9 
8 to8 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. 
