The word leaven, as applied to baking, means to lighten dough (i.e., cause it to rise), either chemically, or biologically. There are 3 types of leavening in baking. First, the “unsung” leaveners: These are the leavening agents inherent in the ingredients themselves, and in how they maximize trapped air when they’re combined. Next are the biological leaveners: yeast, both wild (sourdough), and domesticated. Finally, chemical leaveners include baking powder, baking soda, and their chemical siblings.
- The most basic leaven is simply the air that is captured in a dough or batter. This air is created and trapped by a number of different processes while dough is being mixed.
- beating and creaming
- Don't minimize the importance of these steps; give them the time that's required. Electric mixers have greatly simplified the task of beating sugar, butter and eggs into a light and creamy emulsion for cake, or of making egg whites into meringue. When a recipe calls for 10 minutes of beatingdo it!
- Fluff up your flour before sprinkling it into a measuring cup. Aerated flour will get whatever you're baking off to a much lighter start. (One of the first things a King Arthur employee learns when taking our basic bread-baking class is to take a flour scoop and fluff up the first several inches of flour in its container.)
- The way you incorporate fat into a dough or batter also increases the amount of air you add. Creaming butter and sugar together incorporates air, both through the action of the beaters, and because jagged sugar crystals “grab” air as they come to the surface. Vegetable oil will produce a heavier product because it just doesn’t contain as much air as butter. Also, the water in butter, when heated in the oven, expands and turns to steam; this also helps create a lighter baked good.
- Most recipes calling for eggs have them beaten until they’re light and lemon-colored; that’s the signal that they’ve incorporated an appropriate amount of air. Egg whites can be beaten until they’ve ballooned with air and become meringue. And if you beat eggs together with fat (e.g., creaming eggs and butter), you produce an emulsion that can hold more air than either alone.
- Cool liquids have more oxygen than warm ones. We're not advocating cold necessarily, but use cooler (cool tap water, milk from the fridge) rather than warmer, unless directed otherwise.
- Dry sugars will capture more air in a batter or dough than liquid sweeteners. This isn't to say you shouldn't use honey or molasses or maple syrup; when liquid sweeteners are used, the recipe calls for another type of leavening to raise the batter sufficiently.
- wild yeast
- Wild yeast is a ubiquitous part of nature; a small, one-celled plant, it lives on many growing things, including grapes (where it manifests itself as the powdery sheen on a ripe grape), and grains. See Sourdough, chapter X, for more complete information on wild yeast, and how to use it in bread-baking.
- domestic yeast
Domestic yeast is wild yeast that’s been captured and “domesticated” by a yeast manufacturer. Each yeast manufacturer works with basically the same strain of yeast, saccharomyces cerevisiae; but how each cultivates the yeast to produce a final product is what differentiates the different yeasts produced by different companies.
Most chemical leaveners are fairly modern, having been developed in the last 200 years. They were seen as a more “controllable” substitute for yeast, and it was originally thought that chemical leaveners would completely replace yeast. But instead they’ve created a baking category of their own, leaving yeast to continue the good work it’s been doing for so long.
Chemical leaveners work by first being mixed into the batter, where it dissolves and begins its work. Triggered by moisture, heat, or both, the leaven begins to release carbon dioxide, which then dissolves in the batter’s liquid. Once it saturates the liquid, it begins to devolve into the bubbles of air captured in the batter. The carbon dioxide inside the air bubbles causes them to expand and, as they heat in the oven, they continue to expand until the batter around them bakes into a firm structure. That’s how chemically leavened baked goods rise.
Below are the most commonly used chemical leaveners. Each has its own characteristics, some desirable, some not. Let your knowledge be your guide.
- baker’s ammonia
- Ammonium carbonate or ammonium bicarbonate, which we know as baker’s ammonia, is an old-fashioned leavener not usually available in stores, although it can be found in some pharmacies, baking supply companies or catalogues. The positive attribute of baker's ammonia is that, unlike modern baking powders, it leaves absolutely no chemical residue at all in finished baked goods, neither smell, taste, nor color. It has a fast reaction time and while the release of gases (as a result of the chemical itself, plus heat, plus liquid) produces a telltale ammonia smell, this odor disappears once baking is complete, producing wonderfully crisp cookies and crackers. Baker's ammonia is used mainly in thin cookies and crackers, and sometimes in cream puffs and éclairs. It shouldn't be used in cakes or thick and/or moist cookies, as the ammonia won't have time to evaporate. Due to the unfamiliarity most bakers have with it, and its somewhat tricky nature, baker's ammonia should be used only in recipes calling for it.
- baking soda
Sodium bicarbonate (or sodium acid carbonate), is a natural alkaline ingredient derived from an ore called trona. The bulk of it is mined in the Green River Basin in Wyoming by Church and Dwight Co., makers of Arm and Hammer Baking Soda.
A finished product made with baking soda usually is associated with a slightly coarse or shaggy texture. Baking soda works by reacting with the naturally acidic ingredients in a dough or batter (e.g., buttermilk, sour cream, citrus juice or, less obvious, brown sugar, chocolate, or molasses). It releases most of its gas immediately when combined with an acid and moisture, and a bit more when heated. Try to get a baking soda dough into the oven as quickly as you can, as it begins losing its leavening ability as soon as it's mixed. If all the baking soda isn't neutralized, meaning there’s not enough acid to balance it, the final baked product will have a slightly soapy taste, and a brownish-yellow cast. To balance baking soda, use 1/2 teaspoon baking soda with the following: 1 cup yogurt, buttermilk, sour milk or citrus juice; or 3/4 cup honey or brown sugar; or 1/2 cup un-dutched (natural) cocoa.
- cream of tartar
- This is another natural ingredient, a fruit acid that accumulates on the inside of wine casks as the wine matures. It’s one of the ingredients that, along with baking soda, goes into baking powder. Cream of tartar is often used to stabilize meringue, as its acid helps strengthen the proteins in the egg white, allowing them to trap more air as they’re beaten.
- double-acting baking powder
- Most baking powder on the market today is double-acting; this means that its reaction occurs in two stages, using two different acids. One acid reacts very quickly and, when combined with a liquid, helps to aerate the batter. The second acid is slower-acting, and begins to release carbon dioxide only when heated. This one-two kick is an advantage for several reasons. It gives the baker more flexibility; items such as baking powder biscuits may be made ahead, then refrigerated before being baked, and still have some chemical “kick” left by the time they hit the oven. Since double-acting baking powder includes a perfectly balanced amount of acid and soda, you don't need to worry about a soapy aftertaste (as long as the baking powder is evenly distributed).
When a recipe calls for baking soda, you can always choose to use baking powder instead. However, since the baking powder possesses an inherent acid/base balance, any acidic ingredient in the dough won't be neutralized, and will therefore have a more prominent flavor. If you like the slightly acidic flavor of buttermilk, and your recipe calls for baking soda to neutralize it, try using baking powder instead, which will allow the flavor of the buttermilk to be more assertive.
In general terms, up to 1 teaspoon of baking powder or 1/4 teaspoon baking soda is sufficient to leaven 1 cup of flour in any given recipe. If you want to use baking powder as a substitute for baking soda, you'll need about four times the amount of baking powder as baking soda called for in the recipe: e.g., 1/2 teaspoon baking soda = 2 teaspoons baking powder.
Substituting baking soda for baking powder is a bit trickier. You can make the substitution successfully only if there's enough acid present to react with it; don't substitute baking soda for baking powder in a recipe without some clearly acidic ingredients.