FOOD. 



125 



"gluten." The different grains in common use for food have, when 

 dry, the following average composition, according to Payen. 



COMPOSITIOX OF THE CEREAL GRAINS. 



Thus, of the cereal grains, oats contain, next to wheat, the largest 

 proportion of nitrogenous matters ; but they also contain a considerable 

 abundance of cellulose, or indigestible vegetable tissue, which inter- 

 feres with their nutritive quality as human food. Indian corn is espe- 

 cially rich in fatty ingredients, while rice consists mainly of starch, and 

 is the poorest of all in both nitrogenous and fatty ingredients. 



Wheat is more valuable than the other cereal grains for making 

 bread, not only on account of its larger proportion of albuminous 

 matter, but also on account of the peculiar glutinous quality of this 

 ingredient, which is useful in giving to the dough a proper consistency. 



In preparing the wheat, the grains are first cleansed from husks and 

 adherent foreign material, ground into meal, and the finer and whiter 

 portions from the interior of the grain separated, by sifting and bolting, 

 from the coarser external parts, or bran. Thus purified, the flour 

 consists of starch, gluten, diastase, dextrine, a little fat, sometimes a 

 trace of sugar, mineral salts, and about 15 per cent, of water, which is 

 never wholly expelled by ordinary drying. For making into bread, the 

 flour is mixed with about one-half its weight of water, and kneaded 

 into a flexible dough of uniform consistency. The next process is the 

 fermentation of the dough. For this purpose a little yeast is incor- 

 porated with it, and the mixture allowed to remain for a few hours at 

 a temperature of about 25 C. During this time the sugar originally 

 present in the flour, and that produced from the starch and dextrine by 

 the action of the diastase, passes into fermentation under the influence 

 of the yeast, and is transformed into alcohol and carbonic acid. The 

 alcohol is dissipated by evaporation ; but the carbonic acid, generated 

 in small gas-bubbles, is entangled by the tenacious gluten of the flour, 

 and the dough is thus puffed up into a spongy, reticulated mass. When 

 the fermentation of the dough is completed, it is placed in ovens, and 

 baked at a temperature of 210 C. The effect of this is to cook the 

 glutinous part of the dough, communicating to it an agreeable flavor, 

 and at the same time solidifying it ; so that the baked loaf, when cut 

 open, retains its spongy texture. It is thus made easy of mastication, 

 and readily permeable by the digestive fluids. The spongy texture 



