Why does my cake sink in the middle?

The four causes — opening the oven, underbaking, too much raising agent and overbeating — and how to tell which is yours.

Difficulty: beginner
Time: 30 min
Read: 3 min

Short answer

The structure set before it could support itself, or it never set at all. The usual causes are opening the oven door early, taking it out underbaked, too much raising agent, or too much air beaten in.

A sunken cake rose and then collapsed, which means the structure failed. When it sank tells you why.

Step by step

Note when it sank.During baking usually means the oven door or too much raising agent. As it cooled usually means underbaked. That distinction narrows it immediately.
Keep the oven door shut.For at least the first three quarters of the baking time. The cold air collapses a structure that has not yet set, and it is the single most common cause.
Check your oven temperature.An oven thermometer. A cool oven means the structure sets too slowly to hold the rise, and many domestic ovens run well away from their dial.
Test properly for doneness.A skewer into the centre coming out clean, and the top springing back when pressed lightly. Time alone is unreliable.
Measure the raising agent accurately.Too much makes the cake rise faster than the structure can set, so it collapses. Level teaspoons, and check the baking powder is still active.
Do not overbeat once flour is in.Beat the fat and sugar thoroughly, but fold flour in gently. Overbeating after the flour develops gluten and knocks the structure about.
Check the tin size.A mixture in too small a tin rises high and collapses. Follow the stated tin size, or reduce the quantity to suit what you have.
Weigh accurately.Cake baking is a ratio. Too much liquid or sugar weakens the structure. Scales rather than cups.
Cool it in the tin briefly.Ten minutes in the tin before turning out. Moving a hot cake too soon can collapse a structure that is still setting.

Tips

Do not open the door before three quarters of the baking time. It causes most sunken cakes.
Sank while baking points at the oven or raising agent. Sank while cooling points at underbaking.
Test baking powder in hot water — it should fizz vigorously. Old raising agent is a common hidden cause.

Common mistakes

Opening the oven to check early — The rush of cold air collapses a structure that has risen but not yet set. Use the oven light and resist until the last quarter of the baking time.
Adding extra raising agent for a better rise — It makes the cake rise faster than the protein and starch can set, so it overreaches and falls. More raising agent produces a worse rise, not a better one.

If it doesn't work

Sank in the middle while cooling

Cause: Underbaked — Fix: Bake longer and test with a skewer rather than by time.

Sank suddenly during baking

Cause: Oven door opened, or too much raising agent — Fix: Keep the door shut and measure raising agent level.

Domed then cracked and sank

Cause: Oven too hot — Fix: Check with an oven thermometer and reduce the temperature.

Dense as well as sunken

Cause: Overmixed after adding flour — Fix: Fold the flour in gently rather than beating.

Sinks every time regardless

Cause: Oven running cool, or old raising agent — Fix: Check both. An oven thermometer and fresh baking powder solve most persistent cases.

Questions people ask

Can I rescue a sunken cake?

Not structurally, but a sunken centre makes an excellent base for a filled cake — level it, fill the dip with cream and fruit, and it becomes deliberate.

How do I know if my baking powder is still good?

A teaspoon in hot water should fizz vigorously and immediately. A weak reaction means it has lost potency, which is a common cause of poor and inconsistent rises.