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This is the chocolate cake I baked:
enter image description here
Notice the dark layer at the bottom. I followed this recipe (used only half of all ingredients, since the recipe is for making batter that fills two 9 inch pans). The vegetable oil I used was refined sunflower oil. I whisked the batter manually with a whisk, for less than 2 minutes. The 22L oven was pre-heated for around 7 minutes. I poured the batter into the pan, slammed it on the kitchen counter a few times to get rid of bubbles and placed it in the oven.
Since the cake shown on the page that hosts the recipe does not have a separate dark layer at the bottom, I'm assuming I did something wrong with the cake I baked. On eating it, it tastes delicious and appears to be fully baked.

Question:
Does such a layer form due to inadequate whisking? Is it primarily the oil or egg that has settled to the bottom, and is it because the batter is runny? How do I get it to be uniform?

Surprising detail: The piece of cake kept on top, does not have the dense layer for an inch along the left edge. Also, the dense layer seems to increase in height as it reaches the middle of the cake.

Extra info in response to comments:
This is a standard sponge cake I baked 2 months ago (my first attempt at baking a cake). Used parchment paper lining (the paper jutted into the cake, which is why you see a crevice at the side). Had whisked the egg whites for a long time with an electric mixer. The baking powder and baking soda are old. I do believe the upper and lower heating elements of the oven work fine. For both cakes, I poured the batter into an aluminium pan, placed the pan onto the baking tray provided with the oven, and inserted the baking tray into the center slot of the oven, with the top and bottom heating elements active. Now I noticed that many people keep the pan on a metal mesh/rack, and I wonder if my mistake was in using the baking tray instead of the metal rack which might've done a better job in transferring heat to the bottom of the pan.
enter image description here

Chocolate cake recipe used:
For anyone who isn't able to access the website.
Ingredients:

  • 2 cups sugar
  • 1.75 cups all-purpose flour
  • 0.75 cup Hershey's Cocoa
  • 1.5 tsps baking powder
  • 1.5 tsps baking soda
  • 1 tsp salt
  • 2 eggs
  • 1 cup milk
  • 0.5 cup vegetable oil
  • 2 tsps vanilla extract
  • 1 cup boiling water
  • Heat oven to 350°F (177°C). Grease and flour two 9-inch round baking pans.
  • Stir together sugar, flour, cocoa, baking powder, baking soda and salt in large bowl. Add eggs, milk, oil and vanilla; beat on medium speed of mixer 2 minutes. Stir in boiling water (batter will be thin). Pour batter into prepared pans.
  • Bake 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pans to wire racks. Cool completely. Frost with "Perfectly Chocolate" Chocolate Frosting.

Updates:
Experiment 1:
Used an electric mixer to beat the batter and baked the cake again. Waited till the thermostat switched off and waited a bit more before putting the pan in. (I made a mistake with the first chocolate cake. The aroma of chocolate batter being baked, is similar to a burning smell. Also, one of the reviews of the recipe says that the cake exploded. So due to the smell, and when I saw 4 large bubbles forming at the top of the cake 10 minutes into baking, I had lowered the temperature to less than 175°C for a while). But this time I kept the temperature steady throughout, and here's the result. I added a butter + milk powder + water + sugar + vanilla ganache, because I forgot to add vanilla to the batter. It seems like the ganache has penetrated 1cm into the cake.
enter image description here

  • Observation 1: The baking powder used for all these 3 cakes, has a manufacturing date of July 2013 (best before 24 months from manufacturing date). The baking soda was made in August 2020 (best before 20 months from manufacturing date). So expired baking soda/powder wasn't the issue.

  • Observation 2: As one keen person observed and mentioned in a now-deleted comment, the first chocolate cake had risen and sunk. Also, as noted in the "surprising detail" above, even at the bottom layer, one inch is properly baked toward the edge. So I'm inclined to believe the problem was with heating. Especially since the layer increases in height toward the center.

  • Observation 3: As rumtscho mentioned, the problem could also be due to inadequate mixing. The large bubbles that formed during the first chocolate cake baking, were also a result of inadequate mixing. I'll try some experiments in the next few months to confirm.

  • Observation 4: Heat transfer to the bottom of the pan is fine when the pan is placed on a baking tray. No explicit need to place it on a metal rack.

Experiment 2:
Like the first time, I whisked the batter using a whisk for 2 minutes instead of using an electric mixer. This time, I waited until the oven was heated properly, before putting the pan in, and I maintained the temperature at 180 throughout. It didn't form the layer at the bottom.
enter image description here

Conclusion: It was the lowering of the temperature in-between, and the fact that I didn't wait until the oven got hot before putting the pan in, that caused the layer to form. However, comparing with the texture of the cake in experiment 1, it's necessary to use an electric mixer to get a cake that's well-blended and well-risen.

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  • I have a few recipes that always bake up like that. One of them is a really dense molasses banana bread. I suspect it’s a combination of the leavening, the temperature baked (a bit cooler, so it doesn’t get a ride from evaporation), and the depth of the batter being baked.
    – Joe
    Commented Oct 16, 2023 at 17:44
  • Everybody, please don't post your suspected reasons in comments. They are intended to go into answers.
    – rumtscho
    Commented Oct 17, 2023 at 7:51
  • I've made that recipe many times and never had this problem, so it's almost certainly not the recipe's fault. :)
    – Marti
    Commented Oct 17, 2023 at 18:02
  • If it was down to insufficient whisking, you should at least be able to fling it at a blander for an hour or so. Of course that's not quite the same, but experimenting with an hour or so of actual hand whisking might be a real nuisance… Commented Oct 17, 2023 at 22:01
  • Have you confirmed that the ingredients are still fresh? This looks like a lack of rising. I've had similar results with expired flour or bad baking powder/soda. (Edit: I see now you said the baking powder/soda are stale, try again with a fresh batch. Confirm the other ingredients, particularly the flour as well) Commented Oct 17, 2023 at 22:21

4 Answers 4

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I suspect what's happened here is that your oven wasn't hot enough, so your cake didn't rise and cook quickly enough and collapsed. The uncooked layer at the bottom shows it was much cooler underneath.

7 minutes isn't enough on any oven I've ever seen. It's not just about the air temperature inside, the body of the inside of the oven has to heat up to that temperature as well, so give it 15 minutes preheat instead. Then when you bake it check the internal temperature of the cake with an instant read thermometer, most cakes are done at about 205°F/96°C, give or take a couple of degrees depending on recipe.

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  • Isn't the oven preheated when the thermostat clicks off?
    – RonJohn
    Commented Oct 17, 2023 at 2:28
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    @RonJohn in theory, if the indicator is actually connected to the thermostat. Or at least the air in the oven is, at the position of the sensor. If you want all the metal to be hot so it doesn't cool so much when you open it and let the hot air out, it's best to wait longer, even until the thermostat goes off, on, off a second time
    – Chris H
    Commented Oct 17, 2023 at 6:00
  • @ChrisH yet we must eat sooner than later. :D
    – RonJohn
    Commented Oct 17, 2023 at 6:11
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    @RonJohn I did a lot of testing of my oven, and some other people's ovens, with a high-sensitivity electronic thermometer. What I found was that ovens generally report being "at temperature" when they're still 50F low. After this, I developed the practice of waiting for 5-10 minutes additional.
    – FuzzyChef
    Commented Oct 17, 2023 at 17:21
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    @RonJohn: As a blatant example, if I throw a frozen pizza stone in the bottom of the oven and the thermostat measures the air temp at the top, then you definitely cannot assume that the stone and the air will have the same temp when the thermostat turns off. Sure, I cherrypicked an extreme example, but the point is that a thermostat is biased towards what it's near to, and the exponentially increasing effort to increase the coverage of what the thermostat checks is simply not cost-effective for most everyday oven manufacturers.
    – Flater
    Commented Oct 17, 2023 at 22:43
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Here's what I would take as next steps for troubleshooting this cake:

  1. Check oven heating: is your oven temperature accurate? Is it heating from both the bottom and the top, or just from the top?

  2. Check that your baking powder is still good.

While there are some weird things about the Hershey's recipe, it's been tested by thousands of bakers so the recipe as-is works. Given that, one likely cause of this kind of density is that your leavening is inadequate. For this recipe, most of the leavening comes from the baking powder, so if that's expired/deactivated, the cake would be extra dense.

The second possibility is that your oven is working poorly. For example, if your oven is too cool and only heating from the top, you'd get a cake that was fluffy on top and dense at the bottom.

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    I'd be suspicious of the "7 minutes preheating". Every (electric, also some gas) oven I've ever owned has an indicator connected to the thermostat, and they all take longer than that. Cakes are one thing that need proper preheating.
    – Chris H
    Commented Oct 16, 2023 at 19:23
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    Ah, I missed that instruction. Yeah, even my fairly high-end oven takes about 20 min to actually reach temp.
    – FuzzyChef
    Commented Oct 16, 2023 at 21:44
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    When you mentioned heating at the bottom, I remembered that I placed the pan on the baking tray that was provided with the oven. There's a metal rack also that's provided with the oven. I'm wondering if I should have placed the pan on the metal rack, to allow heat to reach the bottom of the cake more easily. Worried if that'd conduct too much heat, and burn the bottom of the cake. Especially since the pan is made of Aluminium.
    – Nav
    Commented Oct 17, 2023 at 6:22
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    Nav: well, you can find out, if you're willing to risk wasting more ingredients. Your first step, though, should be to get an oven thermometer.
    – FuzzyChef
    Commented Oct 17, 2023 at 17:03
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This is due to the batter's properties, and it's connected both to the runniness and to the whisking, but at the same time, it's not because of them, in the sense that there are many cakes with runny batter that bake up well, and many cakes stirred by hand that bake up well. It's just what happened this time with this batter.

This kind of thing happens when the batter is sufficiently runny and contains two different phases that aren't perfectly dispersed in each other. The heavier one sinks down before the batter firms up in the oven, and the lighter one floats on top. The effect is even used on purpose in some recipes.

The phases can be made up of different ingredients. I've had this happen once, with a recipe I bake frequently, when I made it with a different, coarsely ground flour. The flour didn't hydrate properly in the fluffy batter and sank during the baking, making this gummy layer below. But in other cases, it can be normal batter on the bottom and whipped eggwhites rising to the top, or some other combination of ingredients settling down. I can't even guess at what can it be in your case, because the recipe can't be opened in Europe. Even with reading the recipe, my guess would have very low confidence.

If the recipe wasn't intended for a hand whisk, then it's very possible that making it with a mixer can prevent the problem next time. Once you disperse everything sufficiently well, it will likely stay in suspension until baked, unless you introduce some other unexpected factor, like the coarse flour in my example.

I don't think that a baking powder problem is very likely. If the baking powder doesn't work, the cake tends to be uniformly stodgy, not just the bottom layer. But it's not impossible, so it won't hurt to make sure you're using a new, properly stored package. But really, you should try to use taste and touch and the steps and ingredients of the recipe to find out what is in that wet bottom layer, and then make sure it's mixed in differently next time.

Update your whisking was indeed inadequate. The original recipe recommends 2 minutes of mixing by an electric mixer (not a blender), and you say you mixed for under 2 minutes by hand. 2 minutes by mixer would translate into at least 10-15 minutes of very energetic hand whisking - maybe try making a batch of whipped cream by hand to find out roughly how long you need and at what speed. This is the first thing I'd change when trying again, and err on the longer side after it has failed once.

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  • FWIW, the recipe does recommend using a mixer.
    – FuzzyChef
    Commented Oct 17, 2023 at 17:47
  • @Nav I wouldn't bother investing the time and money and take the risks needed to circumvent geofiltering simply to read a recipe, and I think many other people wouldn't do it either. Thank you for copying it into the post. I added an update to the answer after seeing the recommended mixing in the recipe text.
    – rumtscho
    Commented Oct 17, 2023 at 18:02
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Though I've never had a cake separate into layers like that, I have made one that didn't rise properly. I read an article by a pro baker to find out what happened. The next time I baked it I did the following:

  1. Sifted my flour directly into the measuring cup and leveled it off.
  2. Creamed my butter or oil and sweetener and eggs with an electric mixer a long time.
  3. Used brand new baking powder
  4. Had all ingredients at room temperature It turned out great.

You want lots of air in the batter to help it rise, so use an electric mixer and don't try to get any bubbles out. And yes, only put it into an oven that's fully heated to the right temperature.

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