11. You mishandle egg whites.
Result: The whites won’t whip up. Or, overbeaten or roughly handled, they produce flat cake layers or soufflés with no lift.
Properly beaten egg whites are voluminous, creamy, and glossy, but they require care. First, separate whites from yolks carefully, by letting the whites slip through your fingers. A speck of yolk can prevent the whites from whipping up fully.
Let the whites stand for a few minutes―at room temperature they whip up better than when cold. Whip with clean, dry beaters at high speed just until stiff peaks form―that is, until the peak created when you lift the beater out of the bowl stands upright. If you overbeat, the whites will turn grainy, dry, or may separate.