Like any sane person, I lie in bed at night wondering what the inside of a cake should actually look like. More specifically, I think about the bubbles. Because every time I make a layer cake, when I cut off the tops of each layer of cake to level them and even them out, I get a glimpse of what the interior of the cake looks like, the bubbles, and the “crumb”. Sometimes the bubbles are teeny tiny, quite even, and hardly noticeable. Other times, the bubbles are uneven, mostly tiny but with a few larger holes, even though I was careful to bang the filled tins on the counter several times to push out trapped air before sliding the layers into the oven. Every time I slice off the top of a cake, I ask myself: is this what cake is supposed to look like inside? I think, in a perfect world, every time we slice into a homemade cake, the bubbles would all be teeny tiny and quite even. So I had to ask the question: what’s up with the bigger bubbles in some (but not all) of my cakes? Here are the possible sources that I’ve come up with so far, based on a lot of reading and a lot of thinking, for the uneven holes in cakes. If you have any thoughts on this (or if you also contemplate the bubbles in cake like I do!), feel free to leave me a comment because I would LOVE your opinion on the subject.
Enemy #1: Gluten
The number one culprit is, most likely, gluten. Gluten is a network of proteins (made up of glutenin and gliadin proteins). The network forms when all-purpose flour comes into contact with water and it’s all mixed well together. The combination of stirring and water allow glutenin and gliadin to assemble into the gluten network, giving batters and doughs elasticity, plasticity, and strength. We think of gluten mainly when we made bread doughs: you have to knead the dough and work it to “develop” the gluten, essentially to help those proteins assemble correctly into a strong network. That network is key—gluten helps bread doughs rise and stay risen (on the counter and in the oven). Without gluten, the pockets of air would break through the dough and escape too easily and your breads wouldn’t rise as well as they should.
In bread, gluten is a good thing. In cakes, not so much.
Overmixing a cake batter can lead to gluten formation, especially if your cake recipe includes water or milk (remember gluten forms when you mix flour and water, and work them together). Gluten in a cake would mean that as the baking powder does its job of forming carbon dioxide so that your cakes will rise, that gluten network will trap those air bubbles and instead of forming lots of tiny bubbles, you will end up with bigger bubbles that stretch out and develop as gas forms and water evaporates. You know you’ve overmixed, when you see “tunneling” in cakes and muffins because often if you slice into a cake baked from an overmixed batter, you will see tunnels where air bubbles were trapped and therefore pushed through the crumb, basically tunneling through your cake. Tunneling is considered a bad thing, and from my experience, the more tunneling you see, the harder (less fluffy and spongy) the cake is and the more gluten was formed from overmixing the batter. Soft, squishy cakes that were mixed just enough have less gluten formed from mixing.
Chemical leaveners, like baking powder
The other source of uneven holes in cakes could be the baking powder and the chemical leaveners you are using. If the baking powder (or soda) isn’t mixed evenly throughout the batter, there could be pockets of it in your batter, which would lead to patches where more carbon dioxide is released, leading to bigger bubbles. When I was at Le Cordon Bleu, they actually made us sift our dry ingredients 3 times, which seemed like a colossal waste of time considering I had 2 hours to somehow produce a beautiful, presentable cake from scratch. In hindsight, the chefs might have recommended triple sifting the dry ingredients together in order to evenly disperse the chemical leavener throughout the dry ingredients. Or they were just making our lives extra difficult. Either or.
Broken emulsion and ingredient temperature
A lot of us bakers, myself included, brush over the importance of the emulsion in the first steps of cake making. An emulsion is a dispersion of tiny droplets of a liquid in another liquid, say oil in water, like when you are trying to make a vinaigrette with white vinegar (which is usually about 5% acetic acid in water) and olive oil, or mayonnaise from egg yolks and oil. If your ingredients are at the proper temperature, and you cream the butter and sugar to aerate it before adding the eggs, slowly, to that mix, theoretically, you should end up with a light, fluffy, yellow-tinged batter that is well aerated and emulsified. If you add the eggs too fast, you risk that the emulsion never form properly or that it breaks. You end up with glossy streaks of water/egg white separating out of the batter. The batter doesn’t look even. Furthermore, if the eggs are too cold, it is highly likely that when you add them to the creamed butter and sugar, the butter will harden and form lumps.Either way, what this means is the batter is uneven, and the crumb/air bubbles in the baked cake will be too. Temperature is key and so is your mixing technique.
There are other possible reasons, obviously….
I’m going to stop here, but there are other culprits for the uneven bubbles inside a cake, and some of them are related to what we’ve discussed above. For example, did you know that overwhipping the eggs when they are added to the creamed mixture isn’t a good idea? Basically, mechanically incorporating too much air at this stage can lead to bigger bubbles in cakes. Too much chemical leavener can also be a problem, again because it’s hard to disperse evenly, but also, it can lead to too much carbon dioxide forming in your cake as it bakes. Too much gas, means too many bubbles that may merge into bigger bubbles. Using a strong flour, like our beloved all-purpose flour that we use for everything. That AP flour has a higher protein content (in Canada, AP flour can have 11% protein or more!): it has more glutenin and gliadin hanging around, which means it’s easier to form gluten when it comes into contact with the other ingredients in your cake batter. There’s a reason why we don’t use bread flour when we make cakes, but perhaps all-purpose isn’t the best either? It’s rather convenient though, and I have mixed feelings about making homemade cake flour from AP flour and cornstarch (but that’s a whole other post altogether).
How to avoid large holes
Achieving an even crumb is simple, and yet it’s not (as you can see, I haven’t quite mastered it!). Of course, the first thing we could all do is make cakes with a lower protein flour, like cake flour. This way, your cake batter will be slightly less sensitive to overmixing because there are less gluten-forming proteins around to worry about. That’s an easy fix. The second thing to do is to make sure you are working with butter that is warm, but not too warm (it shouldn’t be on the verge of melting). At the same time, don’t work with eggs that are fridge cold because that won’t help either. These two ingredients and their temperatures can literally break the emulsion and the evenness of the batter. A last thing to try would be to triple sift the chemical leavener with the flour and salt, but also, to revisit the quantity of chemical leavener necessary in the recipe. In my case, the first and the 3rd recipe were based on the same ratios of ingredients, which means, my mixing technique is at fault (or the temperature of my ingredients). I guess practice makes perfect, even after years and years of baking. Sigh. This just means I need to make more layer cakes, and therefore eat more cake! Yay!
Recipe source for cake in 1st image: Three Earl Grey teas cake
Recipe source for cake in 3rd image: Cranberry cardamom cake with cream cheese frosting