Cream of Tartar

Also known as potassium acid tartrate, this by-product of wine making has an indefinite shelf life if not exposed to moisture or humidity. It can be used to stabilize beaten egg whites, as described, and as an interfering agent in sugar syrups and caramel to inhibit crystallization. I also add a little to the water when baking a cake in a water bath to help prevent the aluminum pans from discoloring.