A crystalline naturally occurring carboxylic acid, (CHOH)2(COOH)2; r.d. 1.8; m.p. 171–174°C. It can be obtained from tartar (potassium hydrogen tartrate) deposits from wine vats, and is used in baking powders and as a foodstuffs additive. The compound is optically active (see optical activity). The systematic name is 2,3-dihydroxybutanedioic acid.