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The Cake Bump

Preview photo by Ginnerobot, thanks to a Creative Commons License. / CC BY-SA 2.0

Preview photo by Ginnerobot, thanks to a Creative Commons License. / CC BY-SA 2.0

By Brian Geiger, contributor

November 5th, 2009

Kitchen Mysteries is a weekly exploration of oddities surrounding cooking and food. They could be recipes that fail when they shouldn't, conflicting advice from different sources, or just plain weirdness. If it happens in a kitchen, and you're not sure why, send a tweet to The Food Geek to find out what's happening.

This week's question comes from Ben by way of Marijean:

Hi, Ben (and Marijean),

When you bake a cake, you are creating a relatively loose mesh of gluten and other proteins and filling it up with tiny pockets of air. Yes, I know that doesn't sound as appetizing as cake normally sounds, and I apologize. The gluten is formed from water meeting with the flour, and the air bubbles generally come from tiny holes poked into the sugar from the creaming process, depending on the type of cake that you're making. You may get a little help from a chemical leavener such as baking soda or baking powder, but the essence is: mesh of proteins, tiny bubbles.

In effect, you have a big net, and in the holes of the net are a bunch of balloons. As the oven heats up, a few things happen. First, the air inside the balloons heat, which causes the balloons to expand, because hotter air likes to spread out more than colder air. Hot air is full of energy and bounces around a lot, and cold air just sits like a lump.If that were all that happened, though, the cake would deflate as soon as it were removed from the oven and given a chance to cool.

The second thing that happens is that the proteins in the mesh set, which means that the net goes from being flexible and ropey to being very firm and inflexible. This way, when the cake cools and the air settles down, the structure doesn't collapse.

The whole thing works because the air expands at a lower temperature than the proteins setting. The problem that you're experiencing is that the outside is setting much more quickly than the inside. The reason for this is because the oven uses radiant heat to cook. Well, unless you have a convection oven, then it also uses convection to cook, but don't worry about that right now. The radiant heat hits your pan, which is metal or glass, and heats the pan. It also hits the top of the cake, which heats less quickly than the pan because cake isn't really a good conductor, like metal, nor is it particularly transparent, like glass. So the side of the cake that is only cake and not pan stops a lot of the energy from reaching into the other parts of the cake.

To a certain extent, you are somewhat doomed. The shape of a standard round, square, or rectangular cake is not going to cook evenly, because there's no way to transmit heat in an even manner to the center of the cake pan. Bundt pans and tube pans try to mitigate this by having some pan in the center of the cake and thus making it a topologically simpler problem to solve, but let's go with the harder case of the round, square, or rectangular pans.

So, there'll always be some rise in the center, but there are ways that you can mitigate the extra height. First, you can lower the temperature of the over 10-25°. It might be worth checking the oven temperature to ensure that your oven is cooking at the temperature the recipe calls for, as ovens tend not to do a good job at temperature regulation, and presuming you're using a good recipe, they will have picked a good temperature for that kind of cake.

Second, you can use a lightly-colored aluminum pan. These aren't as easy for cake removal purposes as a dark, nonstick pan would be, but the light color of the sides of the pan will reflect heat away from the cake, thus slowing the setting of the interior of the cake.

Ultimately, though, if you're going for a perfectly flat cake-top for decoration purposes, your best bet is to use a serrated knife and slice off the troublesome bump before icing the cake. This will fix all imperfections, and once the icing is on, no-one need know. This is standard procedure for cake decorators, because, as I said, the problem is not one that is easily solved by baking alone.

Of course, I'm not a master baker, so if any of you have any other hints as to how to even out the cake level just with the baking or the preparation of the cake, please leave some wisdom in the comments.



posted in: Blogs, food geek, cake, temperature, gluten, protein, radiation, convection
Comments (11)

Meatrabbits4All writes: I always just flipped the top layer upside down and filled the gap with icing (who doesn't like more icing?).

The other way is that, when you cut off the bump, you wind up with a hard-to-frost crumby you cut off the bump from both layers and flip the top layer onto the lower. No nasty bumpy crumbs in the icing, no humps in the middle, and a happy cook with cake in their teeth. :) Posted: 8:43 pm on January 18th

briedle writes: A few things we do at my work...After depositing the batter into the greased pan, spin it. Doing this will help the cake climb the sides of the pan. Another thing, flip the cake over onto a sheet pan when you take it out of the oven. This may help level out the top of the cake. We usually still end up with a little bump, but all of our cakes are decorated, so the tops are cut off and sold with icing. Posted: 6:56 pm on January 13th

DMae writes: Hello - I took a cake class at a local school a few years back. The instructor told us not to grease the sides of the pan, only to grease the bottom. His theory was that the batter needs to 'climb' up the sides and the grease keeps it falling - hence the higher center and denser sides. This has worked well for me. I just make sure to run a knife around the sides when it first comes out of the oven, wait 10 minutes before flipping it out onto a wire rack to finish cooling. Great looking flat layers with perfect texture.
Deb Posted: 4:13 pm on January 13th

RandomScraps writes: As always, your mileage may vary, but what worked the best for me when I did a lot of wedding cakes and the like was to

a)Lower the over temperature 25 degrees
b)Use the Wilton strips that pin around the pan (used to be a Wilton instructor, btw, and yes, they do work--they're shiny and silver and remind me of the heat-proof asbestos-like bags we used to put our curling irons in back in the 90s)
c)Cover the cake with a dishtowel the moment the cake comes out and GENTLY press down any remaining hump that might have formed because of not doing the first 2 steps above or because you just couldn't be bothered (watch out for steam holes--namely the one cause by a cake tester breaking the surface of the cake). Just one press will do, not too rough, and then remove the towel and let cool as usual.

Posted: 1:28 pm on November 13th

AuntJenny writes: (hee!)

"Crucial" barely scratches the surface, Brian. Rose will absolutely change your life (baking-wise, that is).
Posted: 6:44 pm on November 10th

LisaWaddle writes: Andy,
I had never seen the Wilton Cake Leveler...very interesting. I agree that trimming the top allows quality control of cakes. Much like frosting on the beaters, it's a lagniappe for the baker! Posted: 10:43 am on November 10th

TheFoodGeek writes: Well, I mean, if it's *crucial*…

Posted: 8:45 am on November 10th

AuntJenny writes: Brian, "The Cake Bible" is a crucial kitchen tome (Beranbaum's mixing technique for butter cakes is nothing short of revolutionary), but her new book, "Rose's Heavenly Cakes" is just as wonderful (she has a German chocolate cake formula that uses unwhipped egg whites as a leavener and it is AMAZING). Get thee to Jessica's Biscuit or Amazon immediately and prepare yourself to be astounded! Posted: 6:19 pm on November 9th

TheFoodGeek writes: It's nice to hear that there are some tools for those who need level cakes.

AuntJenny, I have Rose Levy Beranbaum's Pie and Pastry Bible, but don't have her cake book yet. I'm sure I'll pick up a copy sooner or later.

I should also mention that someone on Facebook suggests that the bump is both good and necessary, as it allows the baker to verify the quality of the cake without damaging the look. But it's great that we have options for cakes both with and without any frosting. Posted: 8:50 am on November 8th

AuntJenny writes: Rose Levy Beranbaum is THE cake diva/guru, and she turned me on to the wonders of the wrap-around cake strips "BasementBaker" references. I've never had the sink-in-the-middle issue he mentions, but have managed to turn out professional-looking, even layers every time. You can even make your own strips in a pinch-- soak folded-up paper towels in water, then wrap them in foil and wind them around your cake pan. Keeping the outside edge of the pan cooler allows for more even rising-- I've even gotten lovely, even layers in sponge (genoise) cakes!
Posted: 2:06 pm on November 7th

BasementBaker writes: Hey Brian - Bake-even strips work fairly well, although when I used them they actually caused the center to fall a bit more than the outer edge. Some people don't like them, but I think they work pretty well. Another tool that I like is the cake leveler from Wilton. It takes a little getting used to, but it works - well, it works best on cakes with higher amounts of fat - not so great with sponge cakes.

Andy Posted: 12:56 pm on November 6th

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