Getting to Know: Leaveners

Sodium bicarbonate—baking soda— produces carbon dioxide when activated with moist, acidic ingredients like buttermilk, lemon juice, or sour cream. This gas physically causes batters to rise, and the heat of the oven sets the risen batter. Use too little and you don’t get enough lift; use too much and the bubbles will burst, leaving your baked goods flat. Baking soda also makes doughs more alkaline, which encourages browning.

Ammonium carbonate—also called baker’s ammonia or hartshorn—isn’t used much in this country anymore, but it’s still common in Greek and Scandinavian baking. It adds lift to thin items that benefit from a lighter texture (like crackers) and don’t need to grow much in size. It gives off an initial ammonia odor during baking, but the odor dissipates quickly, leaving no off-flavor in the baked goods.

Baking powder is a combination of baking soda, acid salt (such as cream of tartar), and cornstarch. Since baking powder contains acid already, it only needs moisture to activate. We recommend using double-acting baking powder, which reacts immediately when mixed with liquid and then a second time when exposed to heat. Date your baking powder when you open it; its leavening power declines noticeably after 6 months.

Also known as rapid-rise yeast, instant yeast is dehydrated to the same concentration as active dry, but by a gentler, less-damaging method. As a result, rapid-rise yeast can be mixed directly into other ingredients, and you can use less without a reduction in leavening. We prefer rapid-rise yeast in the test kitchen for its potency, convenience, and clean flavor. This yeast has a long shelf life and can be stored, unopened, for up to two years.

Yeast is a living microorganism that leavens by ingesting sugars in the flour and expelling carbon dioxide. This process takes time, whereas chemical leaveners can work immediately. Also called cake or compressed yeast, fresh yeast has a crumbly, soft texture that dissolves easily in warm liquid. Fresh yeast is a powerful leavener, but its short shelf life (about two weeks in the fridge) makes it impractical for most home uses.

A mix of flour and water provides a home for wild, naturally occurring yeasts and bacteria to collect and grow. Over about 10 days, with daily doses of flour and water “refreshments,” the yeasts and bacteria ferment, transforming sugars in the flour into carbon dioxide gas and lending complex flavor and tang to the mix. A portion of this starter is then added to bread recipes. True sourdough breads contain no other leaveners.

Active dry yeast has been 95 percent dehydrated into tiny granules. This intense process damages some of the cells while others become dormant, so we “proof” the yeast in warm (about 110 degrees) water before adding it to the rest of the ingredients; the yeast will start to bubble when it activates. To substitute rapid-rise yeast in recipes that call for active dry, use 25 percent less than called for. All types of dry yeast stay fresh longer when stored in the refrigerator or freezer.

While not a leavener per se, cream of tartar (or potassium acid tartrate) is the acidic component in baking powder that allows it to activate without an additional acid. Cream of tartar is a helpful pantry ingredient in its own right; its acidic nature lowers the pH of egg whites, which creates more volume, greater stability (they’re less likely to weep), and a glossier appearance when they’re whipped for soufflés and meringues.

Beer’s carbonation makes it a good choice for leavening batters for fried onion rings and tempura-style vegetables. The carbon dioxide bubbles add lift to the batter as they escape and evaporate in the hot oil environment. Beer’s acidity also keeps these batters tender, since the low pH inhibits gluten formation. We use beer in the light batter for our California Fish Tacos (see related content.)

As you whip egg whites, their proteins loosen and stretch, trapping air inside a fluffy foam. While air is the actual leavener that gives angel food cakes, sponge cakes, and some pound cakes their lift, egg whites or whole eggs are usually necessary to provide the foaming ingredient that captures the air and traps it in the batter. See for yourself in our Rolled Soufflé for a Crowd (see related content.)