Buttercream is a general term that includes several varieties of frosting. They are all made by emulsifying solid fat with liquid to form a thick, creamy paste that you can use to cover and decorate cakes for all occasions. Because buttercream is usually used for celebration cakes, such as wedding or birthday cakes, it is rarely eaten immediately. How long you can safely let buttercream sit out depends on which type of buttercream you have and how long you need to store it.
Buttercream purists don't always agree that American frosting actually counts as buttercream, but it is the most common frosting home bakers use to decorate cakes. It is made from shortening or a mixture of shortening and butter, confectioners sugar, milk, flavorings and food coloring.
American frosting is made with milk, which can spoil quickly in warm weather. The U.S. Department of Health and Human Services recommends refrigerating products made with milk within two hours.
Italian, Swiss and French buttercreams are all built on the concept of a meringue, in which you slowly incorporate a sugar syrup into whipped egg whites before adding softened butter, flavorings and food coloring.
These types of buttercream frostings are more difficult to make, but are less likely to spoil when left out because the hot sugar syrup cooks the eggs in the meringue. You can leave this type of frosting unrefrigerated for two to three days.
If you need to store your buttercream for up to two weeks, refrigerate it in an airtight container. You can also make buttercream several months in advance and freeze it.
Thaw frozen buttercream in the refrigerator overnight. Let chilled buttercream come to room temperature on the day you plan to use it, then briefly re-beat it to restore its texture. Do not attempt to re-beat cold buttercream, or the emulsion may break, separating the buttercream into butter solids and liquid. If this happens, warm the outside of the mixing bowl, and slowly continue to re-beat until the buttercream comes together.
Storing a Decorated Cake
Ideally, you should serve a cake the same day you frost and decorate it. Of course, this is not always possible, especially if you have to travel to the wedding or celebration.
If you have decorated your cake using a meringue-style buttercream, you can leave it at room temperature for two or three days. Beyond this point, the cake will begin to go stale. If possible, refrigerate the individual cake layers until a few hours before the celebration. If you are making a stacked cake, stack the cold layers, and give the entire cake several hours, depending on its size, to come to room temperature before serving.
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