The most common complaints I hear from people who struggle with frosting are that it doesn’t hold its shape on the sides of the cake or that it loses the definition of the border once it has been piped. When the frosting “runs” down the sides of the cake or the border “melts” away, the problem usually lies with the structure of the frosting rather than the decorating technique.
Structure is a matter of balance, fat, temperature, mixing, etc. When one factor gets out of balance, the frosting becomes too soft and runs or collapses upon itself. The first thing to consider is the temperature and consistency of the base of the frosting, whether that be butter or cream. If the base frosting is too soft to begin with, you will end up with a frosting that is too soft. A simple test is to scoop up some of the base frosting on a spatula and see if it will hold a soft peak. If not, you know that your finished frosting will be too soft.
Take a moment to test the base frosting before you proceed. If the frosting is too soft, you will need to add more powdered sugar or stabilizer. Do not add too much at a time or the frosting will become too stiff or separate. Add a little, mix well and then check again. Mix in small increments until the desired consistency is achieved. Working in a warm environment or with warm hands can cause the frosting to soften as you mix. Do not keep mixing the frosting when this happens, thinking that you can mix it back to the right consistency.
Instead, stop mixing and refrigerate the frosting for a few minutes before continuing to mix slowly. Take some time to play with a small batch of frosting, working only on developing the proper consistency and how the frosting behaves when pressed. Pipe a border onto a countertop and let it set for a minute or two to see how it holds up.
Then mix a second batch, this time using a slightly warmer or cooler temperature and mix for a slightly different amount of time to see the difference in the finished frosting. If your frosting still will not hold its shape, do not throw it away and start over. First check the temperature of the frosting. If it is too warm, refrigerate for a few minutes. If the frosting is still too soft after chilling, you may have added too much liquid or incorporated too much air into the frosting as you mixed. Add a little more powdered sugar or stabilizer and mix slowly until the frosting comes back together. With patience, practice and persistence, you will soon master the perfectly pipable frosting.