A crumb coat is a baker’s trick for sealing in the moisture of a cake, and for making frosting the cake much easier. It seals in any crumbs so these later don’t show up when you frost your cake. It is a thinned layer of frosting applied to the cake, as it is almost cool, or just cooled. This layer is allowed to set for one to two hours before the cake is frosted and decorated.

Crumb coat frosting can be of any type, but should not interfere with the taste of the frosting you later will use to frost the cake. You can use either commercially prepared or homemade frosting for the crumb coat. Homemade frosting is often easier to thin than is frosting in a can because homemade varieties don’t contain fillers that can break down when extra liquid is added. If you plan to use a frosting type with egg whites, you might want to make a simple buttercream glaze for the crumb coat.

The consistency of crumb coat frosting should be just barely thick enough to spread on a cake. Here, your goal is not to provide the wonderful thick frosting that will later top the cake, but instead merely the thinnest of layers. You can thin the frosting by adding either water or milk until the frosting resembles a glaze. Once you have applied the crumb coat, patience is required. You have to let the frosting set so that it feels hard to the touch. If you skip this part, the crumb coat won’t provide you with the desired results, and the cake may actually be harder to frost.

Adding a crumb coat is also an important step if you plan to cover a cake with fondant. Fondant will work much better on a cake when it can adhere to the thin layer of frosting. Patience is again required to allow the frosting of the crumb coat to set. Some bakers suggest applying two layers of crumb coat, sometimes called a sticky coat, to cakes topped with fondant. You should wait about two hours in between applying the first and second coat.

With fondant, you can also make a crumb coat out of jam, which can add a nice flavor to the cake. Alternately, consider lemon, orange, or another flavored glaze to boost the total flavor of the cake. Fondant is usually simply sweet and not very flavorful, so it helps to have a crumb coat base that tastes good.

You don’t need to use a crumb coat on cupcakes, or on any cake you plan to serve quickly. Square or oblong cakes that are not taken out of the pan don’t require a crumb coat. Yet for those cakes where you really want to showcase the frosting, the crumb coat remains a great way to get started on a beautifully frosted cake.