noun
Etymology: part translation of French acide lactique
: a hygroscopic usually syrupy alpha-hydroxy acid CH 3 CH(OH)COOH that readily undergoes self-esterification when heated and is known in three optically isomeric forms: (1) the dextrorotatory d- form present normally in blood and muscle tissue as a product of the metabolism of glucose and glycogen; (2) the levorotatory l- form obtained by biological fermentation of sucrose; and (3) the racemic dl- form present in sour milk, beer, sauerkraut, pickles, and other food products and made usually by bacterial fermentation (as of whey, molasses, raw sugar, or starch hydrolysates) but also synthetically, and used chiefly in foods and beverages, in medicine, in tanning and dyeing, and in making esters for use as solvents and plasticizers — called also respectively (1) dextro-lactic acid or sarcolactic acid, (2) levo-lactic acid, (3) dl-lactic acid or ordinary lactic acid ; compare hydracrylic acid