Why Does a Cake Sink?

A cake often sinks shortly after it comes out of the oven because air bubbles inside it suddenly contract or the batter has not set firmly enough during baking. Common causes include opening the oven door too early, measuring baking powder incorrectly, or removing the cake before it is fully baked. These 3 factors, acting alone or together, can make the cake collapse after rising. As the cake bakes, heat causes the baking powder to release carbon dioxide, forming small air pockets that help the cake rise. The proteins and starches in the batter need to set enough to support those pockets. If the cake comes out before it is baked through, its soft interior structure cannot hold them and the cake sinks.

How Can You Keep a Cake from Sinking?
Keep these points in mind for a cake that holds its rise:

• Measure the baking powder as directed; do not add too much or too little.
• Preheat the oven to 170–180°C / 340–355°F before putting in the batter.
• Do not open the oven door during the first 20–25 minutes of baking.
• Check doneness by inserting a toothpick into the center; it should come out clean.
• After removing the cake from the oven, let it rest in the pan for a few minutes, then cool it on a wire rack.

What Mistakes Can Make a Cake Sink?
Opening the oven door repeatedly during baking lowers the temperature and can make the cake collapse. Old baking powder or using too much can cause the batter to rise excessively and then fall. Very cold eggs may keep the batter from mixing evenly. Removing the cake too early leaves its interior structure unset.

What Should You Keep in Mind When Mixing Cake Batter?
Beating the ingredients for too long can incorporate too much air. That air may expand quickly in the oven, making the cake rise too fast and then sink. After adding the flour, mix briefly, just until the batter is uniform. Overmixing can also develop too much gluten and make the cake tough. Pan size matters, too: a pan that is too large for the amount of batter spreads it into a thin layer, which can bake quickly and collapse early. Choose a pan that fits the amount of batter, and grease and lightly flour its base to help the cake release cleanly. Oven temperatures can vary across the oven, so placing the cake centered on the middle rack helps it rise evenly.

A sinking cake is largely preventable: measure the baking powder correctly, preheat the oven, and keep the door closed while the cake bakes. Following these steps helps the cake rise and stay fluffy. Patience is one of the most important parts of baking a cake.