Cream of tartar is a winemaking byproduct. This calcium deposits binds to the wine barrels. Once collected, the deposit is grinded, purified, dehydrated and grinded again into a fine powder. It is used, for example, for meringue, angelfood cakes, souffles, etc.. Cream of tartar helps stabilize the whipped egg whites. Using it prevents whipped egg whites from drying out. You can also uses cream of tartar to prevent sugar crystallization in syrups.