120 FOOD. 



Thus, of the different grains, that of oats contains, next to wheat, the 

 largest proportion of nitrogenous matters ; but it also contains a con- 

 siderable abundance of cellulose, or indigestible vegetable tissue, which 

 interferes with its nutritive quality as human food. Indian corn is 

 especially 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 the purpose 

 of making bread, not only on account of its larger proportion of albu- 

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

 this ingredient, already mentioned. 



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

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

 portions derived 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 fully 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 fer- 

 mentation of the dough. For this purpose a little yeast is incorporated 

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

 perature of about 25 (77 F.). 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, which is 

 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 (about 40(PF.). The effect 

 of this heat 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 substance of the baked loaf, when cut open, retains its spongy and 

 reticulated texture. It is thus made easy of mastication, and readily 

 permeable by the saliva and other digestive fluids. The spongy texture 

 acquired by bread is the main object of its fermentation, although an 

 agreeable flavor is also developed by the process, which does not exist 

 in unfermented bread. The interior of the loaf, in baking, does not rise 

 above 100 (212 F.); the exterior, which is subjected to a higher tem- 

 perature, becomes covered with a crust formed of partially torrefied 

 starch or dextrine, and caramelized sugar. The interior of the loaf also 

 usually retains a little glucose, which is not all destroyed in the process 

 of fermentation. A considerable portion of the water which was mixed 

 with the flour remains permanently united with its organic ingredients ; 

 so that 100 parts of flour will usually yield, after baking, 130 parts, by 

 weight, of bread. 



