Avoiding And Fixing Cake Blowouts

tips to prevent blowouts on fondant and buttercream

Every now and then, a cake that I’m making gets what people refer to as a “blowout,” but which I like to call a “cake tumor.”

It’s so much more descriptive. I don’t want to say that I was lucky to have a cake tumor appear the other day, but it was useful for blogging purposes.

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Why do cake blowouts happen?

Blowouts can happen for a couple of reasons.

Gas inside the cake can make its way out and get trapped inside a layer of fondant, which makes the fondant act like a balloon and inflate in a pocket. This can also happen with buttercream icing, which is what I was using in this case.

It also happens if the fondant is too long for the side of the cake, so that when it starts to settle it can sink below the bottom edge of the tier.

It can end up being pushed out so that it looks like there’s a ridge or a bulge.

If you smooth the fondant down and trim it level with the cake board, that kind of cake tumor is easily fixed.

The inflating gas version is more difficult to handle, because the source of the escaping gas isn’t always obvious, so it isn’t always easy to eliminate.

In this case, it was obviously coming from a soft cream cheese filling that had been compressed when the layers were combined and the cake was stacked.

cake blowout

When I stack cakes, I stack them at room temperature, then let them sit at room temperature for a while just in case this is going to happen.

If you’re working with cold cakes or if you refrigerate a stacked cake right away, it might not have time to develop the tumor…But it WILL develop once you leave the finished cake at the reception and it comes to room temperature!

Better to find out about it when you have a chance to deal with it.

I also press down fairly hard on the layers once the tier is done.

Some people weight the cakes down by putting something heavy on top of the cake after they’ve been filled, but before they’re iced.

The press-down will force air out, and will help get rid of trapped air.

If you have inflating fondant, take a sewing needle and poke it through the bubble.

Gently press the fondant down and let the gas inside the tumor release out of it.

Make sure that the hole is still open, because once gas starts to ooze out it will continue until it’s all gone.

If the cake is decorated in a way that you can do this, it isn’t a bad idea to just make some tiny needle holes all over the cake to begin with, just in case.

It’s like poking holes in potato before you bake it so that it won’t explode.

cake blowout

Blowouts on buttercream.

If you have inflating buttercream, which is what I had in this case, it’s a little more difficult.

You have to poke a hole in the icing and flatten it out, but as we know, icing is difficult to flatten while still keeping a nice smooth surface on it.

The best way to handle this is to just go for it.

Poke a big old hole in the bubble, let all the air out, then smooth it back down for the time being.

The important thing is to leave an escape hatch for any more air to get out.

In this case I took a drinking straw and poked a hole in the area where the tumor had developed, then I left it for a couple of hours.

Leaving it alone will let the air out if more is going to escape.

Once it looks like no more tumors are developing, you can put the cake into the fridge, let the icing harden up, then repair the hole.

I tend to get more cake tumors on any cake that has cream cheese filling than other types of fillings.

I suspect that because the cream cheese is softer, I can’t press down on the layers as hard as I can with other types of fillings, and that means that I more often leave air between the layers.

If anyone has any suggestions for how to avoid this with the cream cheese let me know! Stupid cream cheese…

Fondant cakes warming up.

Fondant cakes develop blowouts fairly often, but I find that it’s more likely to happen when a cold cake warms up.

Since I had to deliver a cake that was refrigerated but would be sitting out in 95 degree heat, I was concerned that a tumor would start to appear.

I’ve heard of people poking holes all over the surface of the cake with a needle to make escape holes for any trapped gas.

This cake didn’t have a lot of places that would hide holes, so I didn’t want to do that.

I decided to just cut a hole in the top tier because the fondant on that tier looked suspicious to me for some reason.


When I put the topper on, I cut a little slit in the fondant right next to the edge of the topper.

It wasn’t obvious, but it would allow any gases that happened to be lurking around in there to escape without creating a bulge.

It’s not something that you have to do, but it can prevent a problem later on.

Tips to avoid cake blowouts.

1. Remember that you can’t 100% avoid a cake tumor from forming, but there are ways to help minimize your risk.

2. Work with cakes at room temperature, since that will allow you to put the cakes together and see what they’re going to do when they warm up at the party site.

Air bubbles are caused when air warms up, expands, and tries to escape from inside of the cake, so give it an opportunity to escape while you’re putting the cake together and not later after it’s all assembled.

3. Make sure that your fillings are as level as they can get before stacking the layers together.

Try to avoid divots where air can get trapped when you place another layer on top of it.

4. When you put your layers together, kind of roll the layers onto each other to push any air out ahead of the layer, don’t just plop them onto each other, which can trap air between the layers.

5. After assembling all of the layers, press gently but firmly on the cake to force out any air that might have been trapped inside the filling layers.

You can even put a book or another weighted item on it for a while to force out any air.

6. When the cake is covered with fondant or buttercream, poke a hole or holes in the outer icing to create an “escape valve” of sorts to allow any air out.

If you’ll be putting flowers on the cake or stacking another tier on top, you can poke holes in the top with a drinking straw.

7. Let the cake sit at room temperature for a while after covering it to allow any air that might want to come out to do so before you start decorating it.

It’s a lot easier to fix an air bubble when the decorations aren’t on the cake yet.

8. After the cake is decorated, refrigerate it so that it will be cold when it’s moved to be delivered.

This will minimize shifting of tiers and fillings, which can prevent trapped air from squeezing out.

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