With or without plans to frost, cooling lets the cake layers form a smooth outer crust, letting you handle the layers without fear of their crumbling or breaking. A cake straight out of the oven has a crumbly, soft crust that would mix with frosting and tear the cake. Cooling also lets steam dissipate from within the cake. This brings it to the desired moist but not damp consistency.

A cooling cake undergoes some compacting of surface crumbs, or crusting. Space constraints and the humidity in your refrigerator make crusting difficult. In an old-fashioned refrigerator with wire shelves, cold air could circulate under cake racks, but modern solid shelves make that impossible. Steam cannot rise easily in cold, refrigerated air, so cake layers may remain damp. Steam that does rise impacts on other items you are storing in the refrigerator.

A warm cake presents two additional problems if hastily frosted. A butter-based frosting will melt, running off or soaking into the cake, leaving a mess. A cooked glaze or frosting may be less runny but can trap steam inside the cooling cake, leaving a sunken middle or pasty-textured center.

To speed cooling, place the cake pans coming out of the oven on footed racks in a draft-free area. This lets air circulate under the pans and speeds cooling and crusting. If you don't have racks, you can set pans on a cutting board covered with a dish towel, propping one edge up slightly with a spoon for a little air circulation. You can also improvise a rack by placing three shallow cans, like those for tuna or sardines, in an open triangle on the counter. Angel food, sponge and fluted cakes need to be cooled with their pans upside down. If your pan does not have cooling prongs, use the can triangle or slide the pan over the neck of a heatproof glass bottle to cool.

After 10 minutes, run a table knife around the edge of the pan. Place a dish towel over the cake layer and the rack on top. Invert the covered pan and remove it gently, leaving the cake layer to finish cooling for another 30 minutes on the towel-covered rack. Allow a full hour for angel food, sponge or fluted cakes to cool.

Brush loose crumbs gently from the cake's surface. To keep crumbing to a minimum, wrap cake layers individually in plastic wrap, then place each on in a resealable plastic bag. Put layers in the coldest part of your freezer for four to 24 hours, then frost.