Egg foam is egg white that has been whipped until it is foamy and stiff — the aerated structure that leavens meringues, soufflés, angel cakes, and mousses. Whipping denatures the white’s proteins, which unfold and link into a network around trapped air bubbles; a little acid or sugar stabilises the network, and the foam grows from frothy to soft peaks to stiff, glossy peaks. The technique is pure protein physics: no chemical leavener, just air held by unfolded albumin. Success demands clean equipment — any yolk fat collapses the foam — and judgement about stiffness, since over-whipping turns the network dry and grainy. Egg foam is the basis of the lightest textures in pâtisserie, the reason a soufflé rises and a meringue shatters. It is also the most temperamental foam in the kitchen.