Cake Bulges - Causes, Prevention & How to Fix It
You’ve baked the perfect cake, let it cool, started filling and stacking it… and then, a little while later, you notice it. A bulge around the middle of your cake.
Don’t panic. Cake bulging is incredibly common, and thankfully, there are a few simple things you can do to prevent it from happening.
Whether you’re making a celebration cake, a wedding cake or simply practising your decorating skills, understanding why cakes bulge will help you achieve those lovely smooth, sharp-edged finishes.
So, why does my cake bulge?
Cake bulging usually happens when the filling between your cake layers gets pushed outwards. This can happen for a few different reasons, but the most common culprit is pressure.
When you stack your layers, the weight of the cake above presses down on the filling. If the filling is soft, too thick, or hasn’t been contained properly, it can slowly squeeze out between the layers. As it does, it pushes against your outer layer of buttercream or ganache, creating that tell-tale bulge.
It can be especially noticeable after your cake has been covered in fondant, as the fondant can make even a small amount of movement much more obvious.
Your filling is too soft
One of the biggest causes of cake bulging is simply using a filling that is too soft.
Buttercream, ganache, curds, jams and other fillings can all work beautifully in cakes, but if they're too soft or runny, they can be pushed outwards when the cake is stacked.
Try to make sure your filling is firm enough to support the weight of the layers above it. If you're using buttercream, allowing it to cool and firm up slightly before filling your cake can make a big difference.
For softer fillings such as jam or curd, consider using a buttercream dam around the outside of the cake layer. This creates a barrier to help keep the filling where it belongs.
You’ve added too much filling
We know it can be tempting to add a generous layer of delicious buttercream or filling between each cake layer, but more isn't always better.
A thick layer of filling means there's more for the cake layers to compress and push outwards.
Aim for a consistent, even layer of filling rather than piling it high in the centre. A cake turntable can be particularly useful here, as it allows you to spread your filling evenly around the cake.
Your filling wasn't contained
If you're using a filling that is particularly soft, piping a buttercream dam around the edge of your cake layer can help prevent it from escaping.
Simply pipe a ring of buttercream around the outside edge of your sponge, then fill the centre with your chosen filling. The buttercream acts as a barrier and helps keep everything contained when the next layer is added.
This is particularly useful when using fillings such as jam, lemon curd or other softer fillings.
Your cake layers aren't level
If your cake layers are domed or uneven, they won't stack as neatly as flat layers.
An uneven cake can put additional pressure on certain areas of the filling, which can contribute to bulging.
Once your cakes have cooled completely, use a good-quality cake leveller or serrated knife to trim away any domed tops. You want each layer to be as level and even as possible before stacking.
Your cake needs time to settle
Sometimes, you've done everything right and your cake can still move slightly as it settles.
Cake layers, fillings and buttercream can all compress and shift a little after stacking. This is why allowing your cake to settle before applying your final covering can be helpful.
Once your cake has been filled and stacked, place it somewhere cool for a while. You can also chill the cake to help firm up the filling and buttercream.
For larger or more elaborate cakes, allowing additional settling time can be particularly beneficial.
How can I prevent my cake from bulging?
A few simple habits can make a huge difference:
- Make sure your cake layers are completely cool before filling.
- Level your sponge layers before stacking.
- Don't overfill between the layers.
- Use a firm, stable filling.
- Pipe a buttercream dam around softer fillings.
- Chill your cake between stages.
- Allow your filled cake time to settle before covering.
- Use a cake scraper to create smooth, even sides.
- Make sure your cake board is sturdy and appropriately sized.
Taking a little extra time during the filling and stacking stage can save you a lot of frustration when it comes to decorating!
What if my cake has already bulged?
If you've spotted a bulge, don't immediately reach for your knife!
First, pop the cake somewhere cool and allow it to firm up. If the filling is still soft, chilling the cake can make it much easier to work with.
Once firm, you can carefully remove any excess buttercream from the outside and smooth the sides again.
If the bulge is particularly pronounced, you may need to carefully remove some of the outer buttercream and assess what's happening between the layers. In some cases, gently pushing the layers back into position once the filling has firmed up can help.
If you're covering the cake with fondant, it's especially important to make sure the sides are smooth and stable before you begin. Fondant won't hide a bulge, it can actually make it more noticeable.
A little patience goes a long way
Cake decorating can sometimes feel like a battle between you and your cake, but bulging is usually nothing to worry about.
The key is to build your cake carefully, use the right consistency of filling, and give it plenty of time to settle and firm up before moving on to the next stage.
And remember, even experienced cake decorators have cakes that don't quite behave themselves from time to time!
With a little practice, you'll soon get a feel for how much filling to use, how firm it needs to be and how long your cake needs to settle.
So next time you spot a bulge, don't panic. It’s fixable and now you know how to stop it happening next time.