Fermentation

(für-men-tā'shun.) [From L.fermento, to cause to boil.] (Chem.) A peculiar change to which certain complex organic bodies are liable, under the influence of an external disturbing force. If to a solution of sugar there be added a little blood, flour, paste, or other putrescible azotized matter, F. will set in, and the sugar will be converted into alcohol, carbonic acid being at the same time disengaged. Nothing acts more powerfully as an exciter of F. than yeast-the matter thrown off by beer when fermenting. A certain amount of heat is required, and the presence of atmospheric air is nece ary at the commencement. In making wine, the vegetable albumen of the must absorbs oxygen from the atmosphere, and thus excites the action of F. in the sugar of the juice, which becomes changed into alcohol. In brewing, the liquor in which malted grain has been infused is caused to ferment by the addition of yeast, and this results in the conversion of the saccharine liquor into beer. In this case, however, the F. is not allowed to run its full course. The beer is drawn off into casks at a particular stage of the fermenting action, and a very slow F. afterwards goes on, which charges the liquor with carbonic acid. F. is also made use of in preparing the weak spirit from grain, which is afterwards distilled into what, when rectified and flavored, is called gin. The preceding are cases of alcoholic or vinous F. Acetous F. takes place if weak alcohol be mixed with a little yeast, or other azotized organic matter, liable to putrefy, and be then exposed to the air. Oxygen is absorbed from the atmosphere, and the alcohol is converted into acetic acid or vinegar. Carbonic acid is not disengaged during this F. Vinegar is usually made either from wine by spontaneous acidification, a isted by a temperature of about 80° F., or from ak ind of beer prepared for the purpose. [s. 361]