Ever wonder why that soufflé puffs up so high? Why does your quick-bread rise? Do you know your baking powder from your baking soda? While some baked products are still unleavened flatbreads such as Matzoh, Mexican tortillas, and the similar chapatis from India, many recipes employ leavening, which is central to both their taste and their texture.

Leavening gases are responsible for the volume in most baked food products; "to leaven" means to make light; to raise. They are responsible for expanding the air bubbles that have been mixed, creamed, kneaded or whipped into the batter or dough. Leaveners also contribute to baked goods' taste, coloring and texture.

The basic leavening gases commonly found in baking recipes are: air; water vapor or steam; carbon dioxide; and biological. In baking recipes, one or more leavening agents participate in the leavening process. However, chemical leaveners and yeast usually are not combined, but there are some recipe exceptions. In some frozen or refrigerated dough found in the grocery store, yeast and chemical leavenings complement each other.

The mechanical action of the whip, tool, hand, etc. will incorporate tiny air bubbles into the recipe. These air cells will expand during the baking process from the leaveners, causing the recipe to rise. The proper whipping of the product and the proper incorporation of air into the batter, usually by folding, are of utmost importance to the leavening of the final recipe, such as with Unshortened (Foam) Cakes. Mechanical leavening is achieved by using different mixing techniques. Examples are:

  • Creaming butter and sugar.
  • Kneading, mixing, beating and stirring.
  • Whipping eggs, particularly separated egg whites, with whipping aids such as sugar and cream of tartar, can easily be beaten into a foam. This method produces particularly light and delicate recipes.
  • Whipping​ aquafaba or the “magic raw egg white replacer.” For those of you who don’t know, aquafaba is simply the juice that forms when beans (legumes) are cooked, either strained from canned beans or when you boil the beans yourself

SARAH SAYS: How beaten egg whites work - When you whip egg whites (albumen), you are really stretching the protein in them. As a result, they unwind and join together loosely, making them unstable. The liquid albumen forms elastic films around the air bubbles beaten into them and essentially trap them, which you can see as a foam. When the foam is heated, the trapped, tiny air cells expand from the heat of the oven and/or carbon dioxide released from baking soda or baking powder, if used, causing a batter to rise. During baking, the egg protein coagulates around them, giving permanence to the foam. Egg whites have a great ability to expand and give volume. However, with the same weight of egg yolk, they are less elastic than the egg whites.

How beaten aquafaba works - SARAH SAYS: I have done some research into how aquafaba, derived from legumes, works. Legumes include beans and peas. Aquafaba is the liquid derived from cooking beans, or from canned beans. Legumes are high in starch and protein.

Steam leavened recipes include pastries, such as with Choux Pastry made with Pâte à Choux dough, and quick-breads such as popovers. The crust traps steam inside, generated from its ingredients. It is this principle, that causes them to become inflated, hollow and stay puffy if properly baked.

Baking powder and baking soda, and their siblings, baker's ammonia and cream of tartar are known as chemical leaveners.

Yeast is the most commonly used leavener in bread baking and the secret to great bread making lies in its fermentation, or the metabolic action of yeast.There are:

  1. Commercial Yeast: Member of the Saccharomyces cerevisiae species and is actually a member of the mushroom family. It posses the basic attributes of all living things, which are respiration and reproduction; and, 
  2. Sourdough Starters or "wild" yeasts (and bacteria): Predominant yeast belongs to the Saccharomyces minor family, and is called Saccharomyces exiguus.