Fermentation
a change which occurs in an organic substance, by which it is decomposed.
Alcoholic fermentation was known to the ancients, and is the change which sugar undergoes under the influence of yeast. Before fermentation takes place, cane sugar is transformed into glucose, thus About 95 per cent. of the glucose is converted into alcohol, Of the other 5 per cent., about 1 part is used by the growth of the yeast, the other 4 parts are converted into succinic acid, glycerin, carbonic acid, and free hydrogen: a larger quantity of these secondary products is formed if the fermentation is slower, or is made with more exhausted and impure yeast. Fermentation takes place most readily at about 24° to 30°. The saccharine liquid becomes turbid, gives off CO2, and becomes comes warmer than the air; when the evolution of CO2 ceases, the yeast or ferment, torula cerevisiæ, separates from the liquid which which now contains alcohol, glycerin, and succinic acid in the place of the sugar. A small quantity of acetic acid is always formed, probably from the decomposition of the yeast.
Most of the natural saccharine juices, as beet-root, potato, and grape juice, when fermented, yield small quantities of alcohols, homologous with ethylic alcohol, forming fusel oil, which contains propyl, butyl and amyl alcohols, also a small quantity of caprioic enanthyl, and caprylic alcohols. FERN Butyric fermentation is the conversion of lactic acid, etc., into butyric acid, due to the presence of Vibrio, according to Pasteur. Lactic fermentation is the conversion of sugar into lactic acid, said to be due to the presence of Penicillium glaucum. It takes place when 2 gallons of milk are mixed with 6 pounds of raw sugar, 12 pints of water, 8 ounces of putrid cheese, and 4 pounds of zinc white; the mixture is kept at a temperature of 30° for some weeks. If the fermentation is allowed to go further, the lactic acid, CH CH OH COOH, is converted into butyric acid, CH₂CH₂CH₂ COOH. Mucus fermentation is the conversion of sugar into mannite, C₆H₁₂O₆, gum, C12H20O10, and carbonic acid, CO2 under the influence of a peculiar ferment. Tannous fermentation is the conversion of tannin, in a solution of galls, into gallic acid, +CO2+2H2O.