Cream of tartar, chemically known as potassium bitartrate, is a white, acidic, crystalline powder derived from tartaric acid and is a byproduct of winemaking. In baking, it stabilizes egg whites to increase their volume and stability in meringues, prevents sugar crystallization in things like frostings and syrups, and is a key acidic component in baking powder.

Uses

Stabilizing egg whites and whipped cream: Cream of tartar helps egg whites and cream whip up faster and hold stiff peaks, making meringues, soufflés, and other light desserts fluffier and more stable.

Preventing sugar crystallization: It prevents sugar syrups from forming crystals, which is useful for making smooth candies, frostings, and certain jellies.

Leavening: As a component of baking powder or when mixed with baking soda, it produces carbon dioxide, helping baked goods like cakes and cookies rise.

Flavoring: It adds a mild, tart flavor to baked goods, such as the distinctive tang of snickerdoodles.

Stabilizing whipped cream: It helps whipped cream maintain its volume and hold its shape.