When considering the many different types of frostings there are for cakes, cupcakes and other baked goods, it's helpful to think about them in six broad categories: buttercream frosting, cooked frosting, whipped cream frosting, royal icing, ganaches, and glazes.
Buttercream frosting itself can be further divided into multiple types, so we'll discuss them first.
Buttercream frosting is by far the most common type of frosting, and it's made by combining some type of fat (usually but not always butter) with sugar. Buttercream sometimes uses eggs to impart a smooth and airy consistency, and the possibilities for adding flavor and color are nearly endless. There are at least five distinct types of buttercream frosting, although it can get confusing since one or two of them are known by multiple names:
- Simple Buttercream: Also known as American buttercream, this one is essentially a combination of fat (e.g. butter) and confectioners' sugar (aka powdered sugar). Optional ingredients include eggs (either whole eggs, just the yolks or just the whites), milk, half and half or nonfat milk solids. Note that cream cheese frosting is merely simple buttercream which uses cream cheese instead of butter as the fat.
- Decorator's Buttercream: One of the issues with buttercream is that butter tends to melt at room temperature, or at least become very soft, which means it's not ideal for producing those decorative flowers and curlicues you see on fancy wedding cakes and the like. The solution is to so-called decorator's buttercream, which instead of butter, is made with vegetable shortening, which has a higher melting temperature. In addition, decorator's buttercream is whipped considerably less than ordinary buttercream. What it lacks in lightness, it makes up for instability, making it ideal for producing those decorative touches. Unfortunately, it also lacks flavor, so it's not uncommon for a small amount of butter to be included.
- Meringue Buttercream: Sometimes called Swiss or Italian meringue buttercream, this variation is made by beating a hot syrup of sugar and water into a basic egg white foam to produce an Italian meringue, and then whipping softened butter into the meringue to make the frosting. Heating the meringue gives it extra stability, which means this frosting is extremely light and airy.
- French Buttercream: This is probably the richest buttercream, and yet it's also extremely light in texture. It's made by adding boiling syrup into beaten egg yolks and then whipping into a foamy consistency, to which softened butter is then added and beaten some more, until light and creamy.
- Pastry-Cream Buttercream: Also known as German buttercream, this variation is made by combining pastry cream (which is a custard with some sort of added starch, such as flour or cornstarch) with butter, and possibly additional confectioners' sugar.
Seven-minute frosting is the classically cooked frosting, and it's made by heating sugar, water and corn syrup to a boil and then pouring this boiling syrup into a bowl of stiff-peak meringue with the beater going. The trick is adding the hot liquid slowly, aiming for the side of the bowl rather than directly into the meringue.
Heating the meringue through the addition of this hot liquid coagulates the proteins in the egg whites, which stabilizes the meringue and helps the frosting hold its shape.
Seven-minute frostings are delicate and can be absorbed into the cake if not eaten the first day. You can use meringue powder to make seven-minute frosting, but note that pasteurized eggs (including liquid egg whites you buy in a carton) will not form as foamy a meringue.
Whipped cream frostings consist of whipped cream, powdered sugar, and flavorings—what could be simpler? As with buttercream, the cornstarch in the powdered sugar helps stabilize the frosting. It's possible to overbeat this type of frosting, which can cause it to turn grainy, so beat just until firm peaks appear when you stop beating and lift the beater straight up from the frosting. Cakes, cupcakes, shortcakes, and cookies with this type of frosting must be refrigerated.
Royal icing is a hard, brittle icing used for decorating cakes and cookies. You can make it from scratch, using powdered sugar, egg whites, and liquid, but many bakers prefer using meringue powder, which is available at bakery supply stores and even some grocery stores. The meringue powder is combined with a liquid, then usually tinted with food coloring.
Ganache is simply chocolate melted with heavy cream. This frosting makes a beautiful shiny glaze on cakes and cookies. If you chill a ganache, beat it until it's fluffy and stiff, then form it into balls, you'll end up with truffles. You can also chill and beat a ganache and use the fluffy result to quickly frost a layer cake.
Glazes are the simplest frostings. Powdered sugar is combined with a liquid to form a thin consistency. Glazes are usually poured or drizzled over the tops of cakes and cookies. This forms a shiny hard crust when the glaze sets. Melted chocolate can be used as a glaze on its own.