Baking Soda and Baking Powder

Baking soda and baking powder are in a lot of baking recipies. But why? And what is the difference between the two?

 

Baking Soda

Baking soda is the common name for sodium bicarbonate (NaHCO₃). This white powder leavens foods. Through a series of chemical reactions sodium bicarbonate is broken down and releases carbon dioxide (CO₂). Bubbles of carbon dioxide are what give cakes, muffins, quick breads and other baked goods their characteristic fluffy texture.

Of course, baking soda doesn’t spontaneously turn into carbon dioxide while it sits on the shelf. To get the chemical reaction to occur there has to be an acid. Acid is present in many foods like cream of tartar, lemon juice, cocoa, or vinegar.

Baking Powder

Baking powder combines baking soda with the acid it needs to create carbon dioxide. To prevent the two components from mixing and reacting in the container, baking powder also has a drying agent such as corn starch. Without moisture, the reaction can’t happen.

If you look at the ingredient list on baking powder, you’ll see some pretty crazy names. Believe it or not, sodium aluminum sulfate (Na₂Al₂(SO₄)₄) and monocalcium phosphate (CaH₄(PO₄)₂) are the acidic conponents. Although both of them react with baking soda to create CO₂, the reactions happen under different conditions. One is slow-acting and the other is fast-acting. Having both makes baking powder more foolproof than baking soda.

Fast-Acting vs. Slow-Acting Acids

Not all acids work the same way. Some are fast-acting and others are slow-acting. Fast-acting means that they react with baking soda right away. Slow-acting acids don’t react with baking soda unless there is heat. The timing of the reaction and creation of CO₂ can effect how food turns out.

Let’s say you are making muffins and the recipe calls for baking soda and a fast-acting acid ingredient like cream of tartar. You put all the ingredients together, put it in a mixer, and forget about it for a while. Those muffins are going to be flat. The baking soda reacted, made CO₂ bubbles, and many of those bubbles escaped out of the batter before the muffins cooked.

If you were using baking powder instead the muffins would only be a little flat. The monocalcium phosphate (a fast-acting acid) would have reacted but the sodium aluminum sulfate (a slow-acting acid) would not have. Only when the muffins are put into the oven will the sodium aluminum sulfate react with baking soda.

 

Substitutions?

Baking soda and baking powder are not interchangable. About half of baking powder is the drying agent, so a teaspoon of baking powder does not leaven as much as a teaspoon of baking soda. In a pinch, you can use one part baking soda and two parts cream of tartar in place of baking powder. Cream of tartar is a fast-acting acid. The mix will not work exactly the same as baking powder because there is no slow-acting acid and the lack of drying agent will throw off the amounts. But it is close enough for most applications. Just don’t store the mix. Without a drying agent the components will react and the mix will become ineffective over time.

 

Summary

Baking soda and baking powder are leavening agents. Baking soda needs an acidic ingredient for it to do its job. Baking powder is a mix of baking soda, acids, and a drying agent. Both leaven by creating carbon dioxide through chemical reactions. Who knew that baking and science experiments were so similar?

 

Photo: Olga Zielinska