A leaven is anything that produces bubbles in dough or batter, causing baked goods to rise. Most breads rise because of yeast, which works by fermenting sugar, which in turn produces carbon dioxide. Baking soda and baking powder are used to leaven quick breads, cookies, and muffins. Baking soda is alkaline and reacts with acid to create carbon dioxide bubbles that become trapped within the batter. It's sometimes used in batters that contain acidic ingredients, like buttermilk or molasses. If there's not enough acid in the batter, the recipe will instead call for baking powder, which combines baking soda with one or more acidic salts. When the baking powder becomes wet or sufficiently hot, the soda reacts with the salts and releases bubbles. Air bubbles can also be trapped in beaten egg whites, a technique used to leaven angel food or sponge cakes.
Originally made from the ground antlers of reindeer, this is an ancestor of modern baking powder. Northern Europeans still use it because it makes their springerle and gingerbread cookies very light and crisp. Unfortunately, it can impart an unpleasant ammonia flavor, so it's best used in cookies and pastries that are small enough to allow the ammonia odor to dissipate while baking. Look for it in German or Scandinavian markets, drug stores, baking supply stores, or a mail order catalogue. Don't confuse this with ordinary household ammonia, which is poisonous. Varieties: It comes either as lumps or powder. If it isn't powdered, crush it into a very fine powder with a mortar and pestle or a rolling pin.Learn more
Baking powder is a mixture of one or more acidic salts and baking soda, an alkali. These two compounds react when they get wet and release carbon dioxide gas bubbles. These, in turn, cause baked goods to rise. Baking powder is perishable. To test a batch, add 1 teaspoon to ½ cup hot water. If it doesn't bubble, throw it out. Look for baking powder among the baking supplies in most supermarkets. Most recipes that call for baking powder intend for you to use double-acting baking powder. This includes two acidic salts--one that reacts when wet and one that reacts heated. By giving the baking soda two chances to react, it usually results in light and airy baked goods. Less common is single-acting baking powder, which only reacts when it becomes wet. When using this kind of baking powder, you have to get the batter into a preheated oven immediately after you mix the wet and dry ingredients together. Aluminum-free baking powder is preferred by many cooks; powders made with aluminum lend an unpleasant flavor to delicately-flavored baked goodsLearn more
Baking soda is alkaline, and when mixed with acidic ingredients, it reacts and releases bubbles of carbon dioxide. These bubbles, when trapped inside batter, help baked goods rise. Baking powder contains baking soda, along with acidic salts that react with the soda when they get wet or heated. Recipes that call for both baking powder and baking soda are probably using the baking soda to offset extra acidity in the batter (from ingredients like buttermilk or molasses) and to weaken the proteins in the flour. Omitting the baking soda from these recipes may alter the color or flavor of whatever you're baking, and make it less tender. Tips: Baking soda is used in devil's food cake because it turns the cocoa powder reddish brown. Vegetables cooked in water mixed with baking soda don't lose as much color, though the baking soda makes them mushier and causes them to lose vitamin C. Sprinkling baking soda on a grease or electrical fire will help extinguish it. Placing an opened box in the refrigerator or freezer will absorb bad odors Baking soda is a good, mildly abrasive scouring powder. Store baking soda in a cool, dry place.Learn more