J: I'm Jeremy Benson from NIU STEM Outreach and I'm in the studio with Kate Powers. This is the Sound of Science on WNIJ.
K: Hi Jeremy, I hear you have a delicious question for me today.
J: That's right! This question is about the chemistry of baking. Lynn wants to know why many recipes call for both baking soda and baking powder. And what's the difference between the two?
K: Lynn's right. Many cookie or cake recipes call for both types of chemical raising agents.
J: Chemical raising agent? Are there other types of raising agents?
K: Sure, lots of bakers also uses eggs for their raising -- and setting -- powers. And baked goods with lots of gluten usually require yeast to create a rise. For cakes, we want a delicate batter that has pockets of air to give them a light airy texture. Chemical raising agents use the same chemistry that happens when we make a kitchen volcano of baking soda and vinegar.
J: When you mix baking soda and vinegar you get a big foaming mess. That's because the baking soda is a base and the vinegar is an acid.
K: Right, acids and bases interact with each other to form carbon dioxide, which is a gas. Baking soda, or sodium bicarbonate, is put into baked goods so the carbon dioxide is formed as bubbles within the batter, making it light.
J: But it needs an acid to react, right?
K: Yep, that's why so many baking recipes call for an acidic ingredient like yogurt, buttermilk or vinegar.
J: Okay, but why the two types of raising agents in recipes?
K: Well, the baking soda reacts very quickly and very early; much of the gas can raise up and out of the batter in the first few minutes of cooking. Baking powder however is frequently referred to as "double acting." Baking powder contains the same sodium bicarbonate as baking soda, but it also contains two types of acid. Monocalcium phosphate and sodium acid pyrophosphate are two acids that don't react with sodium bicarbonate until they become wet, so the combination is shelf stable. But the second acid, the sodium acid pyrophosphate, doesn't react until it becomes wet and hot. The batter will get an initial big burst of raising power when the bases and acids get mixed together with liquid ingredients and put in the oven. And then a slower, longer amount of raising as the batter heats up.
J: So cake is delicious because acids and bases react to make carbon dioxide? I love chemistry. Thanks for the info Kate!
K: You're welcome Jeremy. Keep your questions coming to firstname.lastname@example.org. This has been the Sound of Science on WNIJ.
J: Where you learn something new every day.