In its raw form, Cream of Tartar is a by-product of winemaking. It is powdered tartaric acid that precipitates out of the grapes and is refined for use in a variety of baking applications. It is combined with baking soda to make baking powder and it’s useful as a stabilizer for egg whites in things like meringues. Mixed with water, it becomes a useful cleaning paste for stains. It is also used for making homemade play dough.