As a former biochemistry major, I should be able to remember and understand the difference. Yet, time and time again, I have to look up this information online. The memory retention (lack of that is) in the late 30’s is a truly a frightening thing.
Baking soda or sodium bicarbonate (NaHCO3) is combined with some form of acid such as buttermilk, yogurt, lemon juice, cream of tartar, and vinegar as a leavening agent in cooking and baking requiring fast leavening effect. Some examples are cakes, quick breads, muffins, scones, and cookies.
When baking soda and an acid is combined, carbon dioxide is released quickly and causes the batter to rise. Since the carbon dioxide is released quickly, the main disadvantage of using baking soda is the time between mixing and baking can be critical.
Baking powder is a leavening agent that, basically, already contains the baking soda or the bicarbonate and the acid. The acid can be fast or slow acting. The fast acid reacts in the wet mixture at room temperature and the slow acid reacts will react only when heated. Most commonly used baking powders are called double-acting and actually contain both fast and slow acids. They work in two phases, first in the wet mix when cold and a second time while cooking when hot. This helps to increase the reliability of the leavening effect.
Where I often get confused is when a recipe calls for both baking soda and baking powder. I’ve looked up and read a few explanations, so here’s my basic understanding. Baking powder is the preferred “quick” leavening agent due to reliability. However, many recipes contain acidic ingredients such as the yogurt in a blueberry yogurt muffins. Then, the alkaline in the baking soda helps to neutralize the excess acid.
The general proportion is 1 teaspoon of baking powder to 1 cup of flour and 1 egg. In recipes with acidic ingredient, the baking powder is decreased to 1/2 teaspoon per 1 cup of flour since the yogurt, etc. and baking soda provides the additional leavening effect. You ask, “Why not just use baking soda when an acid is one of the main ingredients?” The use of baking soda alone will not cause enough leavening effect. However, more baking soda cannot be added without adding more acid and adding more acid will change the taste of the recipe.
Phew. Got it? No? Read it a few more times if your brain is slow like mine and it will eventually sink in.
Can you substitute one for the other?
When a recipe calls for baking soda, you can not use baking powder. There will be way too much acid. However, you can use baking soda in place of baking powder by adding some acidic component. In fact, you can make your own “baking powder” by mixing 2 parts cream of tartar to 1 part baking soda. So, when a recipe calls for 1 teaspoon of baking powder, take 1 teaspoon of your mixture.
A final thought since we’re talking about baking soda and powder. How do you determine if the baking soda and powder is still effective? I wonder, especially, about baking powder since with the amount of baking I do, one can will sit in my pantry for years. Simply put a teaspoon of baking powder in some hot water. If it bubbles energetically, it’s still useable. For baking soda, put a small amount in an acid like vinegar or lemon juice. Again, if it bubbles up, it’s useable.