What is cream of tartar used for? Adding a small amount of cream of tartar when you're beating egg whites—usually 1/8 teaspoon per egg white—. Cream of tartar is a popular ingredient in many recipes. What Does Cream of Tartar Do? Cream of tartar is a recipe staple, bonding your ingredients together as a stabilizer. Technically, cream of tartar is an acid—specifically, tartaric acid.