Don’t let the summer’s heat stop you from enjoying a fully frosted slice of cake.
Be it layered or a simple sheet cake, a classic frosted cake is symbolic of celebration; however, nothing about a melted mess of sugar and butter feels celebratory. During warm summer months, the temperature outside can quickly sabotage a beautifully frosted cake. You can almost feel your poor cake sweating out the butter in its frosting within minutes of you placing it into a hot car (in order to take it to a sunny family cookout, no less…). Sure, you can blast the AC and say a few prayers, but taking a few extra precautionary measures, starting in the kitchen, might be a better bet.
Most from-scratch frostings use butter as the base, which renders them rich, but unstable and easily susceptible to melting in warmer temperatures. However, if you want to use a buttercream frosting on your cake, opt for the varieties that are “cooked.” French, Italian, and Swiss buttercreams all include variations of a hot sugar mixture that serves to temper either egg whites, yolks or both—ultimately, creating a more stable icing. For example, when you make French buttercream, egg yolks are whipped until frothy and mixed with a hot sugar syrup that cooks the egg. The mixture is then blended with room temperature butter. Both the Italian and Swiss buttercream follow a similar process. These buttercreams are the most reliable to withstand warm temperatures; that said, you should do your best to keep your frosted baked good in a relatively cool place for as long as possible before serving.
Buttercream + Stabilizers
Any other recipes that involve only confectioners’ sugar blended with butter should be avoided if your cake is going to be exposed to hot temperatures. The American style buttercream is just that—confectioners’ sugar + butter + a little liquid, if necessary. However, since this is the easiest frosting to make on short notice, in a pinch, you can cut the butter in half and substitute shortening, which will make the buttercream more stable. You can also get more staying power by adding powdered stabilizers to your frosting, such as meringue powder, instant pudding mix, gelatin, and agar. If you are only traveling a short distance with your cake exposed to summer heat, you should be fine with the help of one of these additions. Just keep in mind that the addition of stabilizers will extend the frosting's longevity by a little, but not much. You’ll want to avoid using other ingredients that typically need refrigeration, such as cream cheese, yogurt, and whipped cream, as well.
Fondant has a dough-like texture that's created using sugar, gelatin, and glycerol. The pliable frosting is rolled into various shapes and sizes, allowing it to cover a wide range of cakes, giving them a picture-perfect smooth surface. Fondant can be purchased from any cake decor supplier in bulk. For more avid home bakers, fondant is easily made with a combination of marshmallow cream and confectioners’ sugar. Fondant should remain fairly stable and well intact even during the dog days of summer.
I consulted one of our test kitchen’s baking experts, Pam Lolley, and she further suggested skipping the frosting altogether and opting instead for a glaze. A glaze is quick, easy, stiffens within a few minutes, and is unlikely to create an unappealing mess as temperatures rise. Generally, you need about 1 cup of sifted confectioners’ sugar combined with a few tablespoons a liquid such as milk, orange juice, or lemon juice. You can simply pour it over your baked goods to create a simple, sugary topping and be on your way.