Let’s continue the conversation about leavening agents today. Last week, we talked about yeast which is a biological leavening agent. This week, we will discuss the other two most common leavening agents used in home baking, baking soda and baking powder, which are chemical leaveners.
Baking soda is pure sodium bicarbonate (NaHCO3) and is an amphoteric compound, which means it can react as an acid as well as a base. In an acidic solution, baking soda reacts with the acid to form a salt (a compound resulted from the reaction between an acid and a base, not table salt), water and carbon dioxide in gaseous form, which is what we are after in baking. For example, take a look at the chemical reaction of baking soda with acetic acid (found in vinegar):
NaHCO3 + CH3COOH (vinegar) → CH3COONa + H2O + CO2
Try this at home, fill a measuring cup with some water, pour in a half teaspoon of vinegar, and then add a half teaspoon of baking soda, it will sizzle and fizzle, fun!
However, in a basic solution, baking soda will also react to form a salt and only water, no carbon dioxide this time. So if you use baking soda in a recipe that doesn’t have any acidic ingredient, your baked goods will not rise. Another thing to keep in mind is that the chemical reaction with baking soda will start upon mixing, so you will need to bake immediately.
Some acidic ingredients typically used in baking are: buttermilk, yogurt, brown sugar, lemon juice, vinegar…
Baking powder contains baking soda, an acidic component (usually acid salts), and corn starch to keep the mixture dry and prevent premature reactions. Most commercially available baking powders you can find at the grocery store are double acting, which means it contains two acid salts, sodium aluminum sulfate and monocalcium phosphate. Monocalcium phosphate will react with the baking soda upon entering a solution at room temperature, and sodium aluminum sulfate will react at higher temperature during baking. Thus, releasing carbon dioxide in two phases. Because of this, the time elapsed between mixing and baking becomes less critical.
Since baking powder already includes an acidic component, there is no need to use an acidic ingredient in the batter.
Substitution can be made as long as the acidity of the batter is corrected for the type of leavener you are using. Keep in mind that baking powder only contains about 30% of baking soda by weight. So 1 teaspoon of baking powder is equivalent to about ⅓ teaspoon of baking soda. And 1 teaspoon of baking soda is equivalent to about 3 teaspoons of baking powder (or 1 tablespoon). If you are substituting baking soda in place of baking powder, make sure to add an acidic ingredient to your batter. A teaspoon of lemon juice or vinegar will do.