Baking soda is a versatile product with several culinary uses. If your recipe requires it, it probably does so for a good reason and it is better to use it rather than a substitute. None of the alternatives have exactly the same properties as baking soda. This means that all are likely to result in a different flavor and texture than you would get if you used the real thing. That said, consider one of the baking soda substitutes below if using baking soda is out of the question.
Your best bet: Baking powder
Baking powder is the best baking soda substitute simply because it contains baking soda. It is baking soda along with an acidic ingredient that causes the leavening reaction, and a starch to keep them from reacting prematurely. Baking powder has the benefit of not requiring buttermilk or any other acidic ingredient to cause the release of gas that makes your baked goods rise. Baking soda causes your dough or batter to rise when the soda is exposed to moisture, such as when you combine your dry ingredients with your wet ingredients. Most baking powder is double-acting, which means that it causes the baked goods to rise when the baking powder is exposed to moisture and again when the dough or batter is heated. Baking powder can be used in almost all of the recipes that require baking soda.
When using baking powder instead of baking soda, use four teaspoons for every teaspoon of baking soda that the recipe requires.
A decent second choice: Potassium bicarbonate
Individuals must limit their sodium intake often use potassium bicarbonate as an alternative to baking soda. It works in the same way, but does not contain any sodium. Note that you will probably not be able to find it in your local grocery store, but you may be able to buy some online or in a pharmacy. Many pharmacies stock it since it is often used to treat acid reflux.
When using potassium bicarbonate in place of baking soda, note that it does not require the use of an acid to be activated. This means that you may need to replace any acidic ingredients in your recipe with something else.
You do not need to adjust the amount used since potassium bicarbonate works as a 1:1 substitute for baking soda.
In a pinch: Yeast
Along with being the oldest leavening agent in existence, yeast has the benefit of not being a chemical. When used correctly, you can get the desired effects without the bitter taste that can come with baking soda and sometimes baking powder. It is important to note that yeast generates gases by a completely different set of processes and the results may not be the same as you would expect from baking soda. The texture and flavors may be considerably different depending on the recipe. As a result, you may want to try out some test batches if you have time.
When using yeast in place of baking powder, use the same amount that your recipe specifies for baking soda.
If your recipe requires baking soda for its leavening benefits, self-rising flour is a convenient alternative. Self-rising flour consists of baking powder mixed with flour in a specific ratio, which means that it contains baking soda.