2 BULLETIN 701, IT. S. DEPARTMENT OF AGRICULTURE. 
Wheat flour always has been held in high favor as the principal 
ingredient of bread, because in the presence of water the protein of 
wheat yields a tenacious and elastic substance, called gluten, which 
has the property of expanding during fermentation, thus forming a 
network of cellular air spaces throughout the dough. During the 
baking process the gluten is so altered, or "set," that the cellular 
structure is retained, as a result of which there comes from the oven 
a light, porous loaf, unlike that produced from any other cereal flour. 
' FLOUR. 
Standard flour. — As the experiments herein reported were carried 
on intermittently over a period of three years, it was impossible to 
obtain the -same standard wheat flour for the entire series. Conse- 
quently the standard flour, which formed three-fourths of the flour 
content of the breads analyzed, varied in its composition. The flour 
used in making the loaf here designated as the standard contained 
12.50 per cent protein (NX 6.25), while the protein content of the 
bread of this standard loaf as analyzed was 8.74 per cent. Other 
wheat flours used in admixture with the substitutes considered in the 
course of this work varied in their protein content from 11.38 to 
12.63 per cent, the breads naturally showing a corresponding varia- 
tion in the protein content. This accounts for some apparent dis- 
crepancies in the protein content of the breads made with 3 parts of 
wheat flour to 1 part of substitute. 
The substitutes used in these experiments may be classified as 
follows : 
Group 1: Substitutes of low protein content or high carbohydrate 
content. They include the starches from different sources; fruits, 
such as the banana; roots, such as the cassava; tubers, such as the 
potato and the dasheen; and nuts rich in carbohydrates, such as 
the chestnut. 
Group 2: Substitutes obtained from grains and cereals. Among 
these are the common cereals, as well as buckwheat, grain sorghums, 
and millet. 
Group 3: Substitutes obtained from the legumes, including the 
peanut. 
Group 4: Substitutes obtained from certain by-products, like 
bran, wheat germ, cotton seed, peanut oil cake, and soy-bean oil 
cake. Most of these flours or meals were obtained from the trade. 
A few of the experimental flours were prepared in the Fruit and 
Vegetable Utilization Laboratory of the Bureau of Chemistry in this 
way: For Irish potato flour, the potatoes were pared, sliced, cooked 
in steam for about five minutes, then dried, and finely ground. 
The sweet potato flour was prepared by cutting the roots into long 
thin slices, spreading them on trays to dry in a current of warm air 
