Cream of tartar is a by-product of the fermentation process in wine-making, and is useful as a stabilizing and leavening agent in baking. Cream of tartar is the commercial name for potassium hydrogen tartrate.
Cream of tartar is derived from tartaric acid, a substance that occurs naturally in grapes and some other acidic fruits. The acid acts as a preservative in wine-making. Deposits of potassium hydrogen tartrate, or cream of tartar, appear in wine barrels over time. Cream of tartar reacts with baking soda when a person adds liquid, allowing baked goods to rise and become fluffy. It also helps to stabilize egg whites and improve the texture of icing and meringue.