Cream of tartar, (aka potassium bitartrate), is a dry, powdery, acidic byproduct of fermenting grapes into wine. If you're out of cream of tartar there are substitutes. But know they bring some extra flavors to the recipe. It's a good idea to have cream of tarter, if you're planning on making this type of cookie recipe often. 1. Lemon juice - use a 1:2 ratio in baking. Using lemon juice as a cream of tartar substitute is as easy as adding the same amount of lemon juice as the recipe calls for cream of tartar unless baking is involved. For every 1/2 teaspoon of cream of tartar in the recipe, use 1 teaspoon lemon juice. Adds a subtle tangy flavor, similar to cream of tarter, but with a hint of citrus. 2. White vinegar - use a 1:2 ratio in baking. Adds a subtle tangy flavor, similar to cream of tarter.