Old baking powder, an oven cooler than its dial, a pan bigger than the recipe expects, under-creamed butter or a door opened too early. Most of the causes take a minute to check before the next bake.
The eight causes, and the fixes
| Cause | How to tell | Fix |
|---|---|---|
| Old baking powder or soda | No fizz in hot water or vinegar | Replace — 6 to 12 months after opening |
| Oven too cool | An oven thermometer reads low | Set the dial up by the difference |
| Pan too big | Batter less than half the pan depth | Use the recipe’s size — see the pan-size guide |
| Butter under-creamed | Mixture still yellow and dense | Cream 3 to 5 minutes until pale |
| Butter too warm | Greasy, shiny | Use it at about 65 °F |
| Overmixed after flour | Tough, tunnelled crumb | Mix just until combined |
| Too much flour | Dense, dry cake | Weigh, or spoon and level the cup |
| Door opened early | Sank in the middle | Keep it shut for two-thirds of the time |
The equipment causes
An oven cooler than its dial — common in small ovens. An oven thermometer settles it; see how hot does a toaster oven get.
A pan bigger than the recipe assumed, which spreads the batter thin, so it bakes flat. See what pan size does a recipe mean.
A mixer used too briefly at the creaming stage — see how to cream butter and sugar.
The ingredient causes
Leavening past its best. Test it — the FAQ shows how. Cold eggs that curdle the creamed butter. Flour scooped straight from the bag, which packs in up to a quarter more than spooned flour — a scale removes the question; see weighing into the bowl.
How to know it is done
A toothpick comes out clean, the top springs back, and the center reads 200 to 210 °F. See how do I know when a cake is done — an underbaked cake is the most common reason one sinks.
What readers want to know
How do I test if baking powder or baking soda is still good?
Baking powder: stir ½ teaspoon into ¼ cup of hot water — it should fizz at once. Baking soda: add a few drops of vinegar or lemon juice to ¼ teaspoon — it should bubble hard. No fizz means replace it. Baking powder usually loses strength 6 to 12 months after opening.
How do I check my oven temperature?
With an oven thermometer on the middle rack, read 15 minutes after the oven says it is preheated. An instant-read probe is for the food, not the air. If the oven runs cool, set the dial higher by the difference. See how hot does a toaster oven get.
Why did my cake rise and then sink in the middle?
Usually underbaked, or the door was opened too early, so the structure collapsed before it set. Too much leavening does the same: the cake rises fast, then falls. Bake until a toothpick comes out clean and the center reads about 200 to 210 °F, and keep the door shut for the first two-thirds of the time.
Last reviewed 18 October 2026