To create a cake that looks as good as it tastes, it is important the frosting is not runny or sagging on the finished cake. Always beat frosting until it forms stiff peaks to prevent this and allow the frosting to hold its shape. This simple, but necessary step takes between five and 10 minutes of beating using an electric mixer. Once the frosting holds its shape in firm peaks, it is ready for spreading and decorating a cake.
Depending on the type of frosting, it may take as much as 10 minutes of beating to form stiff peaks. High humidity can negatively affect your ability to achieve stiff peaks in your frosting. If possible, make frosting when humidity is low or be prepared to beat it for longer. More important than time, look for the frosting to turn from limp peaks that are rounded on the top and sagging, to those that are pointed and firmly standing upright to judge when your frosting is fully beaten.