Potassium bitartrate

Potassium bitartrate, also known as potassium hydrogen tartrate, with formula KC₄H₅O₆, is the potassium acid salt of tartaric acid (a carboxylic acid)—specifically, l-( + )-tartaric acid. Especially in cooking, it is also known as cream of tartar. It is produced as a byproduct of winemaking by purifying of the precipitate deposited by fermenting must in wine barrels, which arises from the tartaric acid and potassium naturally occurring in grapes.

Approved by the FDA as a direct food substance, cream of tartar is used as an additive, stabilizer, pH control agent, antimicrobial agent, processing aid, and thickener in various food products. It is used as a component of baking powders and baking mixes, and is valued for its role in stabilizing egg whites, which enhances the volume and texture of meringues and soufflés. Its acidic properties prevent sugar syrups from crystallizing, aiding in the production of smooth confections such as candies and frostings. When combined with sodium bicarbonate, it acts as a leavening agent, producing carbon dioxide gas that helps baked goods rise. It will also stabilize whipped cream, allowing it to retain its shape for longer periods.

Potassium bitartrate further serves as mordant in textile dyeing, as reducer of chromium trioxide in mordants for wool, as a metal processing agent that prevents oxidation, as an intermediate for other potassium tartrates, as a cleaning agent when mixed with a weak acid such as vinegar, and as reference standard pH buffer. It has a long history of medical and veterinary use as a laxative administered as a rectal suppository, and is used also as a cathartic and as a diuretic. It is an approved third-class OTC drug in Japan and was one of active ingredients in Phexxi, a non-hormonal contraceptive agent that was approved by the FDA in May 2020.