Cold frosting is difficult to spread over cake and may even tear the cake, ruining your decorating efforts. Store-bought frosting must be refrigerated after it has been opened and homemade frosting will go rancid or melt if left at room temperature, so the problem of cold frosting is a difficult one to avoid. Fortunately, warming frosting is a simple process that does not require any special equipment or skills.
Let frozen frosting thaw overnight in the refrigerator before you attempt to use it. While you may be tempted to speed up the process, applying heat to solidly frozen frosting can cause the ingredients to separate and leave you with a gooey, oily mess. Plan ahead so that you can allow the frosting to thaw slowly and then use one of the following methods to warm the thawed frosting.
Place homemade or canned frosting in a microwaveable bowl and heat it for five to 10 second intervals for 1/3 cup of frosting or 10 to 20 second intervals for 2/3 cup frosting. Stir the frosting with a knife or a large spoon after each 10 second interval until it has reached the desired consistency and temperature. Be careful not to cook the frosting too long or it will eventually melt into a thin glaze. This thin, hot glaze may actually cause your cake or other baked goods to dissolve within two hours of frosting, according to the Betty Crocker website.
Spoon cold frosting into a small saucepan and stir the frosting constantly while cooking over low heat. It is extremely important to stir the frosting constantly during this process or it will scorch and stick to the bottom of the pan. If you have a double boiler, fill the bottom pan with water and warm the frosting in the top pan to reduce the risk of scorching.
Store-bought frosting can be safely left on a warm countertop to warm up after being refrigerated but you must exercise caution when leaving homemade frosting out. The FDA advises that homemade frosting made with perishable items such as cream cheese or whipped cream should not be left at room temperature for more than two hours as bacteria will begin to multiply in the frosting and cause foodborne illnesses.