A cake puffs in the oven, then craters as it cools. What did heat fail to finish?

Answer: Set the crumb scaffold

Trap more oven steam — Steam is part of the lift, not the lasting support. Heat makes water vapor and dissolved gases expand, so the batter can balloon beautifully while it is still weak. Once the cake leaves the oven, vapor pressure drops; if the crumb has not set, those inflated cells shrink like a tent with no poles. More steam would make the timing problem worse, not fix it.

Set the crumb scaffold ✓ — Right: the rise has to be frozen into a solid crumb scaffold. In cakes, heat gelatinizes starch and coagulates egg or gluten proteins, building walls around the bubbles. That is why a cake can look successful at peak puff and still fail minutes later: expansion happened before the structure caught up. The useful mental model is not a balloon but wet foam turning into a sponge.

Dry the center enough — A cake center does need enough heat, but the target is not simply drying it out. Good cake crumb remains moist; it holds shape because starch has gelatinized and proteins have coagulated around the bubbles. An under-set center may feel wet, so this misconception is understandable. The deeper fix is structure, not turning the middle into toast.