Fermentation. The conversion (q.v.) of more or less complex organic substances into simpler ones by the action of viable microorganisms through enzymatic (q.v.) decomposition. The different kinds of fermentation are usually designated by their most important end products, e.g., acetic acid fermentation (q.v.), lactic acid fermentation (q.v.), etc. Alcoholic fermentation by yeast involves the enzymatic conversion of certain sugars, especially dextrose (q.v.), into ethanol (q.v.) and carbon dioxide (q.v.), the process taking place under anaerobic (q.v.) conditions, as when yeast is added to a dough at a suitable temperature, and with adequate sweetener concentrations, supplies of essential yeast nutrients, etc. The most apparent manifestations of such a fermentation are an expansion in dough volume (q.v.) that results from carbon dioxide evolution and the formation of flavor substances, including alcohol (q.v.).