Egg foams

Usually I expand more on the basic topic, but as eggs are one of the most versatile food items, I am going to skip and focus the conversation on information that is relevant to the meringue recipe.

The foaming power of egg whites came around the 17th century. At the time, the fork was a still a novelty. Cooks used twigs, bits of dried fruit, or bundle straw to whip the whites into meringues and soufflés.

Physical agitation usually breaks structure, but in egg whites it actually creates structure. Agitation of the sticky egg white transforms it into white foam, a cohesive structure that holds its own when mixed and cooked.  Whipping exerts physical stress that unfolds the compact protein molecules. Air becomes incorporated into the whites. It creates an imbalance of water and air that promotes bonding of globulin proteins and ovotransferrin. The bonded proteins become a solid network that pervades the bubble walls and hold water and air in place. Thus the egg white becomes a semi-solid mass of minute bubbles called a foam.

Left alone the foam eventually collapses. Heat transforms it into a permanent solid. Ovalbumin does not contribute much to the foam network, but heat makes it unfold and coagulate. In a cooked foam, ovalbumin more than doubles the amount of solid protein reinforcement in the bubble walls. As water evaporates, the semiliquid foam turns into a solid.