A gas in a solid, such as sponge cake, is classified as which type of dispersion?

The correct classification of a gas in a solid, like that found in sponge cake, is known as a foam. In culinary terms, a foam is a stable dispersion of gas in a liquid or solid matrix. In the case of sponge cake, the gas bubbles created during the leavening process are trapped within the structure of the cake, making it light and airy.

Foams are formed when a gas, such as air, is dispersed in a liquid or solid and stabilized by surface tension. The proteins from eggs and other ingredients contribute to the stabilization of the foam as they create a network that holds the gas bubbles in place.

Recognizing the distinct nature of foam helps to understand other types of dispersions, such as sols, suspensions, and colloids, which involve different interactions and states of matter. For example, a sol is a solid dispersed in a liquid, a suspension contains larger particles suspended in a liquid that can settle over time, and colloids consist of smaller particles that don't settle but can scatter light. This emphasizes the unique properties of foams in culinary applications, including how they contribute to the texture and volume of baked goods.