The Boston cooking-school cook book

account of its great power of expansion, it holds the gas developed in bread dough by fermentation, which otherwise would escape. Yeast Yeast is a microscopic plant of fungous growth, and is the lowest form of vegetable life. It consists of spores, or germs, found floating in air, and belongs to a family of which there are many species. These spores grow by budding and division, and multiply very rapidly under favorable conditions, and produce fermentation. =Fermentation= is the process by which, under influence of air, warmth, moisture, and some ferment, sugar (or dextrose, starch converted into sugar) is changed into alcohol (C_{2}H_{5}HO) and carbon dioxide (CO_{2}). The product of all fermentation is the same. Three kinds are considered,—alcoholic, acetic, and lactic. Where bread dough is allowed to ferment by addition of yeast, the fermentation is _alcoholic_; where alcoholic fermentation continues too long, _acetic_ fermentation sets in, which is a continuation of alcoholic. _Lactic_ fermentation is fermentation which takes place when milk sours. Liquid, dry, or compressed yeast may be used for raising bread. The compressed yeast cakes done up in tinfoil have long proved satisfactory, and are now almost universally used, having replaced the home-made liquid yeast. Never use a yeast cake unless perfectly fresh, which may be determined by its light color and absence of dark streaks. The _yeast plant_ is killed at 212° F.; life is suspended, but not entirely destroyed, 32° F. The temperature best suited for its growth is from 65° to 68° F. The most favorable conditions for the growth of yeast are a warm, moist, sweet, nitrogenous soil. These must be especially considered in bread making. Bread Making =Fermented bread= is made by mixing to a dough, flour, with a definite quantity of water, milk, or water and milk, salt, and a ferment. Sugar is usually added to hasten fermentation. Dough is then kneaded that the ingredients may be thoroughly incorporated, covered, and allowed to rise in a temperature of 68° F., until dough has doubled its bulk. This change has been caused by action of the ferment, which attacks some of the