The main causes of bulging cakes I have found are:
- Unlevel or domed cakes
- Not letting the cake rest long enough
- Too much filling
- Under-dowelling
- Cake is too warm
Cold cake is happy cake
Chilling cakes makes them easier to work with and transport, and minimizes bulging. Allow enough time for the cake to come to room temperature before it is served. Occasionally a cake coming to room temperature will develop the dreaded “blow-out”. Minimizing the air trapped inside your cake by following the directions below will lessen the chances of a blow-out. Here is another article specifically focused on blow-outs (notice she recommends many of the same steps below! Air inside your cake is bad!)
To avoid these pitfalls, see the gallery below.