Both baking soda and baking powder, referred to as chemical leaveners, give breads, cakes, and other doughs and batters a light texture by introducing carbon dioxide gas into the batter. The gas expands the bubbles that are already present in the batter due to the action of mixing or creaming. Once the baked good goes into the oven, the heat causes the gas to expand so that the bread rises even higher. Eventually, the other ingredients of the batter settle into a firm structure. These little pockets of empty space cause the baked item to crumble or break apart easily when we eat it.
Baking soda, also known as bicarbonate of soda, needs to come into contact with both a liquid and an acid in order to work. Batters that include buttermilk, yogurt, sour cream, or fruits often call for baking soda. Bakers used to add cream of tartar to react with the baking soda if the recipe didn’t use acidic ingredients, a trick that is reflected in older recipes.
Baking soda reacts immediately when it is moistened in the presence of an acid, and recipes leavened by baking soda alone should be baked soon after mixing to take full advantage of the leavening power.
Baking powder is a mixture of an alkali and an acid, plus cornstarch to keep the powder dry until use. Baking powder begins working when it comes into contact with a liquid, and it receives another boost when it goes into the heat of the oven. This double reaction is why it’s referred to as “double acting.”
When chemical leaveners aren’t fully blended into the batter, they clump together. Biting into a pocket of baking powder leaves a bitter or soapy taste in your mouth. Combine the baking soda or powder completely with the flour by sifting, stirring, or whisking together the dry ingredients before mixing in the remaining ingredients.
Baking soda keeps for up to 2 years if it is stored in a cool, dry place, but it does gradually lose its effectiveness. To test it, mix about 1/4 teaspoon with 2 teaspoons of vinegar. It should foam up immediately.
Baking powder lasts about 6 months. Check it by mixing 1 teaspoon baking powder with 1 cup hot water. If it bubbles immediately, it is still potent enough to leaven a batter.