While breads use yeast—an organic leavener—cookies rely on chemical reactions to give them lift and make them palatable. In this article, we will explore these chemical leaveners and how they work: baking powder, baking soda, and cream of tartar.
Baking soda is a powerful alkaline used primarily to leaven cookies, muffins, and cakes. Because it is alkaline, it reacts with acids in a batter as soon as it is mixed causing bubbling and a thickening of the batter. It does not require the heat of the oven to begin leavening.
Generally, only acidic recipes call for baking soda. Buttermilk, juices, unalkalized cocoa, and molasses are common acids used in baking. The reaction of the alkaline baking soda with an acidic batter has two effects: it creates the carbon dioxide bubbles that leaven the batter and it neutralizes the acid in the batter. Neutralizing the acid changes the taste—buttermilk, for example, no longer has its characteristic acid tang.
Typically, recipes use 1/4 teaspoon baking soda for each cup of flour. Very heavy batters or very acidic ones may use more. Occasionally drop cookies call for more baking soda but that is to allow the cookie to brown more easily. A batter with a lower pH will brown more easily.
While baking soda is alkaline, baking powder is a mixture of an alkaline baking soda and two acids designed to create a neutral compound. It therefore reacts with itself using the moisture of the batter as a catalyst. Like baking soda, this reaction creates carbon dioxide bubbles.
The baking powder generally used in the kitchen is double-acting: it reacts at room temperature in the presence of moisture and again in the oven in the presence of heat. The result is the extra lifting power necessary to make a cake light and airy. Because the baking powder reacts with itself, it does not alter the pH of the batter.
Often a weakly acidic recipe will call for both baking soda and baking powder. The baking soda will react with the acid in the batter but the reaction will not be strong enough and is bolstered with the extra baking powder.
Cream of Tartar
Cream of tartar is a by-product of the wine-making industry and is derived from tartaric acid. As an acid, it is the counterpart to baking soda and when the two are combined they create a chemical reaction which produces carbon dioxide. Most recipes that call for cream of tartar also call for baking soda. In some recipes, cream of tartar is used to increase the acidity in the batter to preserve the tang of buttermilk or an acidic juice used in conjunction with baking soda.
There are other chemical leaveners, though they are rarely used in today’s kitchens. In addition, mechanical means are used for leavening. Creaming butter and sugar together entrains air in the batter. Steam is used to lift products. Egg whites are whipped to capture tiny air pockets and thereby lighten products.
Did you like this? This was excerpted from our upcoming: “About Baking: Ingredients and How They Work.” You will be able to get this handbook free with our next newsletter.