A leavening agent (sometimes
called just leavening or leaven) is a substance used in
doughs and batters that causes a foaming action. The leavening agent
reacts with moisture, heat, acidity, or other triggers to produce gas that
becomes trapped as bubbles within the dough. When a dough or batter is
baked, it "sets" and the holes left by the gas bubbles remain,
giving breads, cakes, and other baked goods their soft, sponge-like
Chemical leaveners are chemical mixtures
or compounds that typically release carbon dioxide when they react with
moisture, heat, and acidity. They usually leave behind a chemical salt.
Chemical leaveners are used in quick breads and cakes. Chemical leavening
- baking powder
- baking soda (a.k.a., sodium
- ammonium bicarbonate (a.k.a.,
- potassium bicarbonate (a.k.a., potash)
- Potassium bitartrate (a.k.a., cream of
- potassium carbonate or (a.k.a.,
- monocalcium phosphate
- Biological Leaveners
Microorganisms that release carbon
dioxide as part of their lifecycle can be used to leaven products.
Varieties of yeast are most often used. Yeast leaves behind waste
byproducts that contribute to the distinctive flavor of yeast breads. In
sourdough breads, the flavor is further enhanced by various lactic or
acetic acid bacteria).
Leavening with yeast is often a slower
process, requiring a lengthy proofing.
Yeast can also be used to make carbonated
beverages like beer, which can then be used as leavening.
Steam and air are used leavening agents
when they expand upon heating. To take advantage of this style of
leavening, the baking must be done at high enough temperatures to flash
the water to steam, with a batter that is capable of holding the steam in
until set. This effect is typically used in popovers and Yorkshire
puddings, and to a lesser extent in Tempura.