Sauces Thickened with Bubbles: Foams

Like emulsions, foams are a dispersion of one fluid in another. In the case of foams, the fluid is not a liquid, but a gas, and the dispersed particles are not droplets, but bubbles. Still, the bubbles do the same thing that droplets do in a sauce: they get in the way of water molecules in the sauce, prevent them from flowing easily, and thus give the sauce as a whole a thicker body. At the same time, they provide two unique characteristics: a large surface area in contact with air that can enhance the release of aromas to the nose; and a light insubstantiality and evanescence that offers a refreshing contrast to the texture of nearly any food they accompany.