baking powder is a dry leavening agent
Baking powder is a dry leavening agent used to quickly introduce carbon dioxide into wet batter, which creates air bubbles that aerate and lighten the material. In short, baking powder helps breads, cakes and other baked goods to expand, or rise, while baking. For this reason, baking powder is also referred to as a raising agent. Because baking powder forces air bubbles into the dough quickly during baking, as opposed to fermentation with slower-reacting yeast, breads made with baking powder are known as “quick” breads.

A wide array of baked goods and yeast free breads can be made to rise, and so become more light, fluffy and palatable, by the inclusion of baking powder. Recipes for muffins, biscuits, cakes and cookies employ baking powder.

Baking powder is comprised of three dry powder ingredients: one that is acidic, one that is base, and one that is filler Most commonly these dry powders are baking soda (base), Sodium Acid Pyrophosphate (acidic) and potato starch (filler) When they are dissolved in water the acid and alkali react and form carbon dioxide, which expands into bubbles to leaven (ferment and rise) the mixture.

In recipes using single-acting baking powder all the carbon dioxide bubbles form when these three ingredients meet with the liquid ingredients, which is why dry ingredients and wet ingredients are kept separate until just before the ingredients are briefly stirred and quickly baked.

baking soda is a component of baking powder
Many people confuse baking powder with baking soda but, even though both are used in baking, these powders differ chemically and promote different reactions. However, baking soda is actually a component of baking powder.

In fact, baking powder generally consists of baking soda (also known as sodium bicarbonate), a weak acid (like cream of tartar) and corn or potato starch. The addition of an acid improves flavor. Otherwise, even though baking soda alone produces carbon dioxide gas, it also releases sodium carbonate, which results in a metallic taste in baked goods. This means that you can substitute baking powder for baking soda in a recipe, but you cannot substitute baking soda for baking powder. Note, too, that the term “double-acting” baking powder indicates that the formula contains more than one acid.

baking soda vs yeast
Some recipes that use baking powder were adapted from recipes originally containing yeast. This was sometimes achieved to yield similar results in shorter amounts of time. Baking powder provides relatively rapid results in recipes compared with yeasted recipes. For making muffins, cookies, quick breads, and creating the "20-minute meal," and when making baked goods for those with yeast allergies, baking powder is an indispensable ingredient.

a short cut to gain some time
Baking powder is such a significant part of the history and production of baked goods and prepared foods that some of its early manufacturers made their fortunes by producing just baking powder.

The creation of baking powder in the mid-19th century made it unnecessary to activate carbon dioxide production with a liquid and an acid, such as lemon juice or buttermilk and cream of tartar. It also meant that the baker didn’t have to scramble to get the batter into the oven before all the carbon dioxide gas escaped into the air.

Some of the baking powders founded in the post-Civil War era are still manufactured today. Among them: Clabber Girl and Rumford Baking Powder.

storage and evaluation
Baking powder can lose its effectiveness if it isn’t stored in an airtight container in a place free of moisture and direct heat or light. To determine if a baking powder is still active, stir a teaspoon into a cup of hot water. If the liquid foams, the powder is still good for use in baking.