Potassium bitartrate, also known as potassium hydrogen tartrate, has formula KC4H5O6. It is a byproduct of winemaking. In cooking it is known as cream of tartar. It is the potassium acid salt of tartaric acid, a carboxylic acid. In food, potassium bitartrate is used for: Stabilizing egg whites, increasing their heat tolerance and volume; Preventing sugar syrups from crystallising; Reducing discolouration of boiled vegetables; Frequent combination with baking soda (which needs an acid ingredient to activate it) in formulations of baking powder. Commonly used in combination with potassium chloride in sodium-free salt substitutes A similar acid salt, sodium acid pyrophosphate, can be confused with cream of tartar because of their common function as a baking powder.