There are a few common reasons why an angel food cake might fall flat after being taken out of the oven:
Underbaking: If the cake is not fully baked, the structure may not have set properly, and it can collapse as it cools. Make sure to follow the recommended baking time in the recipe and use a toothpick or cake tester to check for doneness. The tester should come out clean or with a few dry crumbs attached when the cake is fully baked.
Opening the Oven Door Too Soon: Angel food cakes are delicate and sensitive to sudden changes in temperature. If you open the oven door too early in the baking process, it can cause the cake to collapse due to the rapid change in temperature and air pressure.
Overbeating or Underbeating the Egg Whites: The success of an angel food cake depends heavily on the whipped egg whites, which provide the cake's structure and lift. Overbeating the egg whites can lead to a weak structure, while underbeating can result in insufficient volume. Follow the recipe's instructions for whipping the egg whites to the right consistency.
Incorrect Pan Preparation: Angel food cakes need to "climb" the sides of the pan as they rise. If the pan is greased or has a non-stick coating, the cake may not be able to adhere to the sides properly, and it could collapse as it cools. Use an ungreased tube pan specifically designed for angel food cakes.
Removing the Cake from the Pan Too Soon: After baking, angel food cakes need to cool upside down in the pan. This allows the cake to maintain its volume and prevent collapse. If you remove the cake from the pan too soon, it can lose structure and deflate.
Old or Expired Leavening Agent: If the baking powder or cream of tartar used to stabilize the egg whites is old or expired, it may not function effectively, leading to a collapsed cake.
To improve your chances of success, make sure to follow a reliable angel food cake recipe closely and pay special attention to the instructions regarding egg white preparation, baking time, and cooling. It's a delicate cake that requires precision and careful handling to achieve the desired light and airy texture.