Potassium bitartrate, also known as cream of tartar, is a natural byproduct of winemaking. It is a white, crystalline powder that is soluble in water. Potassium bitartrate is used in winemaking for a variety of purposes, including:
 
Reducing acidity: Potassium bitartrate can be used to reduce the acidity of wine. This is because potassium bitartrate is a salt of tartaric acid, the primary acid found in grapes. When potassium bitartrate is added to wine, it reacts with tartaric acid to form a less acidic salt.
Stabilizing wine: Potassium bitartrate can also be used to stabilize wine. This is because potassium bitartrate can precipitate out of wine when it is cold. This process, known as cold stabilization, can help to remove impurities from the wine and make it more stable.
Promoting malolactic fermentation: Potassium bitartrate can also be used to promote malolactic fermentation. Malolactic fermentation is a secondary fermentation that converts malic acid, another acid found in grapes, into lactic acid. Lactic acid is a softer acid than malic acid, and it can give wine a more mellow flavor.