Why Cakes Sink in the Middle (and How to Stop It)

A cake sinks when the bubbles inside expand before the batter around them is strong enough to hold the shape — or when the structure never fully sets. Every sunken middle traces back to a handful of causes, and each has a clear fix.

1. Expired baking powder or soda

Both lose strength within months of opening. Test baking powder with hot water and baking soda with vinegar — no vigorous fizz, no rise. Replace them every six months.

2. Underbaking

A cake that looks done at the edges can still be liquid at the core, and it collapses as it cools. A toothpick in the center should show moist crumbs, not batter — and the center should spring back when pressed.

3. The oven runs cool (or hot)

Most home ovens are off by 15–25°F. Too cool and the structure sets late; too hot and the edges set while the middle keeps rising, then falls. A $10 oven thermometer settles it.

4. Opening the door early

A rush of cool air mid-rise deflates the fragile center. Keep the door shut until at least 80% of the bake time has passed, then check quickly.

5. Too much leavening or sugar

It sounds backwards, but extra baking powder makes bubbles too big to hold — they merge, rise, burst and collapse. Measure leavening with proper measuring spoons, leveled, and measure flour correctly so the ratios stay true.

6. Overmixed (or undermixed) batter

Overmixing after the flour goes in builds gluten that shrinks and pulls the crumb down; undermixing leaves streaks that bake into weak spots. Mix just until the last flour disappears.