I recently had two cakes that "grew" air pockets under the buttercream. One developed an air pocket after it was already delivered and the other was still in my kitchen. They were both fully decorated. I'm concerned because I have a wedding cake this weekend and don't want to deliver a perfect cake only to find out that it GREW an air pocket between delivery time and guests arriving. Is it a temperature or moisture issue? HELP!
Usually that happens when you do not press the icing well enough against the cake for it to adhere to the cake.
Use a pin and puncture the bubble from the underside, then lightly press out the air.
To prevent it some people prick holes about every inch or two along the bottom and top of the cake which are covered w/the borders.
You probably will get other ideas like the cake must settle over night before you ice it.......I don't agree as I've had similar happen to dummy cakes, using both fondant & b'cream.
Personally, I think it has to do with temp or moisture factors. I used to get these ALL the time until I made sure that I don't apply buttercream until the cakes are at room temp. I also let my cakes air dry about 15 minutes after unwrapping (I bake, freeze, bring to room temp and ice). This has helped SO MUCH. I also make some "air holes" around the bottom, both on buttercream and fondant covered cakes. I understand your frustration -- it's so stressful to have a perfectly iced cake one minute, and then have a side blowing out the next.
When I use an icer tip I get air bubbles, but if I use a spatula and do a little at a time, I don't get bubbles.