462 FIELD AND GARDEN. PRODUCTS 



resulting higher feeding value; but this is not desirable in milling 

 wheat, where the flour is the critical product in determining the 

 value of the manufactured product. 



Fourth, the quality of the flour. This is the dominant factor 

 in determining the real milling value of the wheat. Wheat flour 

 is distinguished from the meals of all other grains by its ability to 

 produce "light bread." Other meals, such as corn-meal, oat-meal, 

 etc., often contain as much, or possibly more, total food materials or 

 nutriment, as does wheat flour, but they will not produce "light 

 bread." "Lightness" is due to imprisoned gas, generated by the fer- 

 mentation of starch by yeast, or produced by baking powders. This 

 same fermentation of starch, liberating bubbles of carbonic acid gas, 

 may be caused by yeast acting on starch in corn-meal, but the corn- 

 meal dough will not become "light" because there is nothing there 

 to imprison them. The substance which is peculiar to wheat flour is 

 this tenacious, elastic material, called gluten, which serves to retain 

 these gas bubbles in the dough during baking. Gluten is not the 

 only valuable ingredient in wheat flour. Starch is just as necessary 

 an ingredient and possibly of even greater food value. But starch 

 can be grown and supplied by many other plants just as easily, and 

 perhaps more cheaply than by wheat. If it were possible to grow 

 a wheat so rich in protein that it would yield flour containing too 

 small a proportion of starch for proper baking qualities, this de- 

 ficiency could easily be overcome by adding starch from some other 

 source. But if, as is often the case, a given wheat is too rich in starch 

 and produces flour yielding too small amounts of gluten, there is no 

 other possible source to get gluten with which to build up this lack 

 and the flour must be poor in baking qualities. Hence it is that 

 the amount of gluten yielded by the flour is properly taken as the 

 measure of the value of the wheat for milling purposes. But it is 

 not alone the quantity of gluten produced which measures the value 

 of the flour for baking purposes. The quality of the gluten must be 

 taken into consideration as well. As will be more fully described 

 in the section on baking tests in this bulletin, gluten is made up of 

 a mixture of two proteid bodies of very different properties, and 

 the quality of the gluten depends very largely upon the proportion 

 of these two which is present in the flour. The quality of the gluten 

 from two different samples of wheat may be very different even 

 though its quantity may be the same. Hence a determination of 

 the total amount of gluten yielded by a sample of flour must be sup- 

 plemented by certain tests as to its quality before a true judgment 

 as to the quality of the flour can be passed. 



The fifth and final factor in determining the milling value of 

 wheat is the color of the flour which it will yield. This is a matter 

 of prejudice alone, on the part of the consumer, and is in part con- 

 trolled by the system of milling employed. Hence, while color is 

 still a factor of some importance in determining the preference of 

 purchasers for certain grades of flour, it is of minor importance in 

 a scientific investigation of the milling values of our wheats. 



