Baking soda is an alkaline compound that reacts to the acidity of other ingredients to produce carbon dioxide. To activate it, you need to have both a liquid and an acid. Acidic ingredients you might have in your kitchen include lemon juice, yogurt, buttermilk, vinegar, brown sugar, and cream of tartar. When baking soda is activated, carbon dioxide is produced. That is what leads to baked goods rising and becoming light and fluffy.
One of the reasons you may end up with a dense pastry after baking is not using enough baking soda. The opposite isn’t true though; too much baking soda will not lead to an extremely fluffy pastry. Too much baking soda can result in a bitter taste.
Baking soda is sometimes referred to as sodium bicarbonate.
Unlike baking soda, baking powder is already combined with an acid. All you need to do to cause a reaction is add liquid. The most commonly used baking powder is double-action baking powder. What is double-acting baking powder? It means that the baking powder allows the dish to rise on two occasions.
In double-acting baking powder, the first rise occurs when baking powder gets wet at room temperature. The first reaction occurs when the powder is combined with a liquid at room temperature, and the second happens when the powder is combined with heat, like when you put the dish in the oven. Most baking powder on the market is double-acting, and will say so on the label.
Single-action baking powder is most often used by professional chefs, and it only has a reaction when heated. Baking powder is used in recipes that do not call for the addition of acidic ingredients. You can use baking powder for quick breads, baked good recipes, and other baking recipes. For example, in a simple biscuit recipe that only calls for baking powder, eggs, milk, and flour, the baking powder reacts with the liquids and acts as the rising agent.