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Steam
Appears in
By Paula Figoni
Published 2003
Steam (water vapor) is the gaseous form of water. It forms when water, milk, eggs, syrups, or any other moisture-containing ingredient is heated. Since the conversion of water to steam is considered a physical change, steam is called a physical leavener. Steam is a very effective leavening agent because it expands to occupy over 1,600 times more space than water. Imagine the power of this huge increase in volume.
All baked goods rely on steam for at least some of their leavening because all baked goods contain water or another liquid. In fact, many baked goods rely on steam for leavening more than one might imagine. Sponge cakes, for example, rely on steam as much as air. That is because sponge cake batters are high in eggs, which are high in water. For steam to be an effective leavening agent, however, the oven temperature must be high enough for water to evaporate to steam at a fast enough rate.