15 Sep Kitchen science fair
I’ve mentioned before that Valerian gets an upset stomach from eating foods that have a lot of baking powder in them. I’d never heard of this reaction before we met; in fact I don’t think I had ever given any thought to the leavening agents I used. I first read up on the chemistry of baked goods to maintain marital harmony. But if you’re ever interested in working out your own recipes, it does help to have a basic understanding of kitchen science to get the best results.
First of all, there’s chemistry. Chemical leavening works through the release of gasses when you mix together (or heat) different agents; these gasses make little bubbles in your batter or dough that give the light texture you’re looking for. Baking soda is straight sodium bicarbonate, and it reacts immediately when you mix it with an acidic liquid. If you’ve ever made a science fair volcano or rocket car by mixing baking soda and vinegar, you know this reaction is fast and powerful. You need the acid from your liquid to get the reaction going, so choose buttermilk, yogurt, sour cream or even orange juice when you bake with baking soda.
Baking powder combines sodium bicarbonate with another acid ingredient (often cream of tartar, which is potassium hydrogen tartrate). You see where this is going – when you use baking powder, the acid is already present, and is just activated when it gets wet; the liquid itself doesn’t need to be acidic to set off the reaction. In double-acting baking powder, a second reaction takes place when you heat the mixture, giving another boost to your batter when you pop it in the oven. You generally need more baking powder to get the same lift as baking soda, about twice as much per cup of flour.
When you use chemical leavening, you need to work fast to take advantage of the gas-producing reaction (Are you giggling? What are you, twelve?), which explains why most muffin and quick bread recipes that use chemical leavening have you mix the wet and dry ingredients separately, then quickly combine them just before you bake. That said, I know from experience that if you only have one muffin pan and have to let the rest of the batter sit while the first batch bakes, it doesn’t make an appreciable difference in the texture of the muffins.
Next up is cookbook physics. While sponge cakes do use a quantity of chemical leavening, what really gives a cake its airy texture is eggs. Eggs contain protein that gives your batter structure; when you beat air into the egg, that protein helps to secure the bubbles that form and expand as the batter is heated. I had trouble with yellow/vanilla cake recipes until I found one that specifies how long you need to beat the butter and eggs – it takes a lot longer than I thought to work the air into your batter! Since it’s the egg whites that have the most protein, they hold bubbles the best. If you look at our recipe for Valeria’s potato torte, you’ll see that the egg whites are beaten separately to give them maximum lifting power. You need to be careful not to break up the bubbles as you’re stirring the mixture together or else you’ll lose that nice light consistency.
Both chemistry and physics come into play when you bake bread. The yeasts in the dough create gas bubbles as they digest the sugars around them, so the dough rises. At the same time, much as the protein in eggs gives structure to a cake, the proteins found in wheat gluten provide structure for yeast breads. Kneading the bread helps line up the gluten into threads or chains that will trap the bubbles made by the yeast.
When you know what’s happening as you mix, you can modify recipes to see what works best. Pancakes are a great place to start experimenting – try making them with milk and baking powder, or buttermilk and baking soda, or even a yeast-based recipe (which we’ll have for you soon) and let the kitchen be your laboratory.