What is a "stiff peak"?

A stiff peak refers to a stage in whipping egg whites or cream when the mixture holds its shape firmly and stands upright when the beaters are lifted. At this stage, the whipped mixture is thick, glossy, and smooth, with peaks that stand straight up without curling over. Stiff peaks indicate that the mixture has been whipped to its maximum volume, and the proteins have formed a stable network that traps air bubbles within the mixture. Stiff peaks are commonly used in recipes for meringues, pavlovas, soufflés, and stabilized whipped cream, where a firm and stable texture is desired.