2 BULLETIN 701, U. 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 hght, porous loaf, unhke that produced from any other cereal flour. 



Standard Jlour.— 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 (Nx6.25), 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 %vith 3 parts of 

 wheat flour to 1 part of substitute. 



The substitutes used in these experiments may be classified as 

 f oUows : 



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, hke 

 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 UtiHzation Laboratory of the Bureau of Chemistry in this 

 way: For Irish potato flour, the potatoes were pared, shced, cooked 

 in steam for about flve minutes, then dried, and finely ground. 

 The sweet potato flour was prepared by cutting the roots into long 

 thin sHces, spreading them on trays to dry in a current of warm air 



