Most cakes require a cooling period before they’re removed from their pans or otherwise handled. Their structures are quite delicate when still hot, but become firm as the starch molecules begin to settle back into close, orderly associations with each other. Pound and butter cakes are fairly robust, their structure coming mainly from gelated starch, and can be removed from their pans after just 10–20 minutes. The sweeter egg-aerated cakes are held up largely by the coagulated egg proteins, which form a more gas-tight film around the gas cells than starch does, and therefore shrink as the gas within cools and contracts. The result can be a collapsed cake. To avoid this, angel, sponge, and chiffon cakes are cooked in tube pans that can be inverted and suspended over a bottle to cool. Gravity keeps the cake structure stretched to its maximum volume while the walls of the gas cells firm and develop cracks that allow the pressure inside and outside the cells to equalize.