Foams

A foam is a type of colloid where the dispersed phase is a gas and the continuous phase is a liquid. One special characteristic of foams is that the dispersed phase does not settle out of the continuous one.

Foams can be made by agitating a liquid which in turn traps air inside the liquid film. As air is trapped in the liquid, the dispersion increases in volume. This effect is known as foam overrun.

Many foods are foams, such as marshmallows, whipped cream, or meringue.

Liquid foams can also be stabilized by adding a substance called stabilizer, which prevents or retards the coalescence of the gas bubbles. Of the great variety of substances that act as foam stabilizers, the best known are soaps, detergents, and proteins.