USE OF WHEAT II7 



energy per unit of flour and is probably to be preferred as the 

 main diet for tlie average person. The digestibility of bread 

 from different grades of patent flour was quite similar. 



175. Amount of Bread from Flour. — Th; value of flour de- 

 pends upon the amount and quality of bread produced. (172) 

 The amount of bread does not, however, depend upon the flour 

 alone but also upon the conditions of baking, chief of which are 

 the percentage of water used in the dough, the size of the loaves, 

 the temperature of the ovens and the length of time of baking. 

 Richardson reports that by differences in these factors the 

 amount of bread may be varied as much as fifteen pounds per 

 100 pounds of flour. For different flours handled as nearly 

 alike as maybe, he obtained variations ranging from 129 pounds 

 to 140 pounds of cold bread for each 100 pounds of flour, and 

 he concludes that the yield of bread is dependent on physical 

 conditions of breadmaking and not to a large extent upon the 

 chemical composition of the wheat (flour).^ It was a fact, how- 

 e\er, that the flour with the least per cent of nitrogen produced 

 the smallest per cent of bread and the flour with the largest per 

 cent of nitrogen produced the largest per cent of bread. As the 

 percentage of flour in wheat is about seventy-two, each pound 

 of wheat produces about a pound of bread. 



176. Milling Machinery. — There are three types of machinery 

 for producing flour which may be represented as follows : 



1. The mortar and pestle, which is the primitive method, in 

 which the force employed is principally that of impact 



2. Burr stones, which was the universal method of milling 

 wheat in the United States until 1878, in which the wheat is cut 

 and crushed. 



3. The roller process, which has made large mills possible, 

 in which the wheat, and subsequently its several parts, pass 

 through a series of graduated hardened steel rollers and in which 



1 U. S. Dept of Agr., Bu. of Chem. Bui. 4, pp. 60-62. 



