How Leavening Works

Hi, I’m Dr. Kiki Sanford. And today on Food Science, we’re discussing the rising power of baking powder. Have you ever wondered why some cookie recipes fall flat while others wind up fluffy? They’re definitely several factors at play but at least part of the answer depends on your ingredients. The most important ingredients to make breads cakes and cookies light and airy are leavening agents. The word leaven actually means to lighten or cause to rise. One common leavening agent, yeast, is biological. But there are also several chemical leaveners. All leavening agents release gas which gets trapped in dough and creates bubbles. The bubbles made by yeast come from CO2 which is released through the process of fermentation. However, this process can be too slow for some kinds of baked goods. Sometimes cooks just need something faster. That’s when chemical leavening agents are useful. If you check the baking aisle in your local grocery store, you’re likely to find baking powder and baking soda tucked away somewhere between the flour and the chocolate chips. These two products are used instead of slow acting yeast for making cookies and quick breads because they release carbon dioxide more quickly. You want to use yeast for making thick dough’s because they’re better able to hold on to the bubbles. The fast action of baking powder and baking soda relies on the process known in chemistry as an acid-base reaction. Acids are compounds that like to give away or donate hydrogen atoms or protons. Bases like to accept protons. When acids and bases interact, they neutralize one another. In doing so, water and the neutral ionic compound they called a salt are created as byproducts. Baking soda or sodium bicarbonate is basic. It’s usually used by itself in recipes that contain anesthetic components such as buttermilk, brown sugar or molasses. The baking soda reacts with the acid to create carbon dioxide, a salt and water. By combining vinegar which is acetic acid with the baking soda, we can watch the reaction take place. I’ll have a half a teaspoon of baking soda, and add it to warm water. No bubbles yet. Now I’ll add a teaspoon of vinegar. Nice and fizzy. The reaction begins the moment the ingredients interact and then ends rather quickly. So if you let your batter sit very long before you put in the oven, it’s possible to loose the benefit of that bubble action. In the case of baking powder, it contains both an acid and a base which react when added to liquid. The base in baking is actually baking soda. And it is usually mixed with the dry acid. Like cream of tartar, otherwise known as tartaric acid, and filler like cornstarch. Cornstarch helps to elongate the shelf life baking powder by absorbing water from the air and preventing the acid in base components from reacting prematurely. However, it is important to test your baking powder before used to determine whether or not it’s any good. Let’s test mine. Remember, baking powder contains both an acid and a base. So all I should need is a little bit of water for the reaction to take place. Water acts as a solvent in which the molecules can dissolve and then react. Just a teaspoon of baking powder per cup of warm water should do the trick. We can see bubbles forming in the water almost immediately. Baking powder comes in several different varieties. The most common one found in stores these days is called double-acting. Less common is the single-acting sort which contains only one acid and one base and reacts only once when added to liquid. Single-acting powders are named for the kind of acid they contain, tartrate or phosphate. Double acting powders have a second acid that’s heat activated, usually sodium aluminum sulfate. So they react and create carbon dioxide during the mixing process just like the single-acting powders. But the second acid is activated during the cooking process allowing further gas release and rising to take place. If you’re ever in a bind for baking powder, you can make your own. To substitute, a half a teaspoon of cream of tartar, a quarter teaspoon of baking soda, and a quarter teaspoon of cornstarch for each teaspoon of baking powder in the recipe. Knowing how baking powder and baking soda interact with the other ingredients and recipes explains why you are told to mix the wet and the dry parts separately. It keeps the acid based reaction from happening too early and your baked goods from falling flat. But remember, it’s not just food, it’s science.