We were curious about why recipes call for one over the other, and we went on a hunt to find out.
Baking soda is also known by its chemist term: sodium bicarbonate. When heated, this chemical compound forms carbon dioxide gas - making your breads and cookies rise. That's not all it produces, though, which can be a problem...
When heated, sodium bicarbonate also produces sodium carbonate, which doesn't taste so great. It leaves an unpleasant, alkaline flavor behind. But if you mix baking soda with an acid (like lemon juice or another citric acid carrier) then the sodium carbonate is partially neutralized and leaves behind less aftertaste. This acid also helps the carbon dioxide gas release more quickly.
Baking powder is basically just baking soda with acid added in. It has just enough acid to use up the sodium carbonate. Shirley Corriher in her great book Cookwise says that 1 teaspoon baking powder contains 1/4 teaspoon baking soda. The other 3/4 teaspoon contains the acid and cornstarch.
Depending on how much acid is in the baking powder (remember how it helps release the carbon dioxide?) the baking powder can be labeled as fast-acting, slow-acting, and double-acting. Most baking powders are double-acting and will release only a small amount of gas during mixing; the majority will release in the hot oven.
This may all be very interesting if you are into food chemistry, but what's the takeaway for the home cook?
First, remember that baking soda works with foods that are acidic. If you are making biscuits that call for buttermilk and baking soda, but you substitute regular milk, your biscuits may not rise. Buttermilk is acidic and releases the raising power in the baking soda. Add a tablespoon of vinegar to each cup of milk.
On the other hand, what if you add an acidic ingredient to a recipe with baking powder? You will need to add a little soda. Let's say you are making cookies and substituting 1/2 cup lemon juice for the water in order to make lemon cookies. The recipe calls for 2 teaspoons of baking powder, but you will need to neutralize the acid in the lemon juice. Substitute baking soda for one teaspoon of the baking powder. Corriher says that baking soda is 4 times as powerful as baking powder, so use only 1/4 teaspoon baking soda for each teaspoon of baking powder in the original recipe.
Originally published January 16, 2008.