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One of the most interesting things I have learned in the kitchen is about leavening agents. I know most people probably don’t give much thought to leavening agents. I know some of the basics of baking are scary to some people. Yeast freaks a lot of people out.(It is a little touchy, but once you start working with it, you realize it really isn’t that complex.) The truth is leavening agents are magical to some degree, helping baked goods to be light and airy. I was blown away when I first found out the leaveners do not actually create new air bubbles in doughs, just help to expand the existing ones. One of the best books I own has some great information on this process - Cookwise by Shirley Corriher. There is a great story in the book about her first finding this out and realizing why her cakes never came out very good. Anyone who bakes consistently realizes the importance of incorporating air into the butter mixture (with 7 - 8 minutes of whipping, often times) for cakes. Shirley realized after doing some research for another article she was writing that she never did this step and that was why her cakes were not that great! I love stories like that, see you can always learn something in the kitchen.
Yeast is interesting and very important to baking. Yeast is a one-celled organism that feeds simple sugar (that’s why you always use honey or sugar to activate yeast). As the dough rest, the yeast eats the sugar around it and in the process gives off gas and grows. The yeast continues to grow dividing to reproduce. Water temperature is important when working with yeast. Water above 140° or so will kill yeast. Cold water only affects the yeast in the initial activation phase. The yeast will not activate in water that is too cold.
So what about chemical leaveners? Baking powder and baking soda also produce gases that help to leaven cakes and baked goods. When heated these chemicals break down and give off gas. Adding an acid to baking soda helps it to give of gas faster and gets rid of the unpleasant taste. Baking powder works much the same way, as it contains baking soda. It also contains an acid in just the right amount to use up the baking soda. There is also some cornstarch used to keep the baking soda and acid dry and separated.