A Speck of Yolk Can Ruin Whipped Egg Whites
Egg white foam depends on proteins unfolding and linking around air bubbles as you whip; fat — even a tiny bit of yolk, or oil residue on the bowl — coats those proteins and blocks them from forming a stable structure, which is why a single fleck of yolk can keep whites from ever reaching full volume. A completely clean, dry, grease-free bowl (copper bowls have a genuine chemical assist, reacting with the proteins to add extra stability) and whites at room temperature both whip up fuller and more stable than cold whites in a greasy bowl.
Sources & methodology: These tips draw on established food-science references —
Harold McGee's food-science writing, America's Test Kitchen /
Cook's Illustrated testing, Serious Eats'
technique reporting, USDA food safety guidance,
and peer-reviewed food-safety research (including UC Davis
cutting-board studies) — not reworded recipe-blog consensus.