Cream of tartar belongs to a category of ingredients called leavening agents. A leavener produces gas in a flour-based food such as bread, cake or cookies, making the food rise. Without a leavener, a scone would not have the light, fluffy texture it is supposed to develop while it bakes. Cream of tartar is a vital ingredient in a scone recipe. If you omit it from your dough, you must substitute an alternate leavening agent.
Giving Rise to Scones
Cream of tartar is an acidic compound that reacts to an alkaline ingredient to form a complete leavening agent. Sodium bicarbonate -- or baking soda -- is the most common alkali in recipes that include cream of tartar. Baking powder is essentially just a mixture of cream of tartar and baking soda as well as cornstarch, which prevents the two principle ingredients from reacting prematurely. To replace cream of tartar in a scone recipe, add the volumes of cream of tartar and baking soda together. Then, substitute a measure of baking powder that equals that sum. For example, if a scone recipe calls for 1/2 teaspoon of cream of tartar and 1/4 teaspoon of baking soda, add 3/4 teaspoon of baking powder and omit the cream of tartar and baking soda.