View transcript
- What's heavier, chocolate cake or flan? When you're making chocoflan, the weight actually doesn't matter, but the density does. Hi, I'm Julie, welcome to Hungry for Science. Today we're gonna use science to look at a very special dessert. Now, my mom's favorite dessert is flan. That might seem surprising for a Taiwanese immigrant, but the texture of flan is very similar to silken tofu that she grew up with. Now my favorite dessert is chocolate cake, so imagine my delight when I learned about chocoflan, which is a dessert that combines both of them. You have a layer of moist chocolate cake on the bottom, and it's topped by a layer of smooth, creamy flan. It's a dessert that's sure to satisfy the both of us. Now, chocoflan is sometimes referred to as an impossible cake or a magical cake. It can't be impossible, but is it magical? Or can we explain what happens through science? The thing that seems magical about it is it actually inverts, the two layers change positions while it bakes. When you make the chocoflan, you pour in chocolate cake batter first, and then you cover it with flan mixture and then while it's baking those two layers switch places and they switch places actually because of gravity. Gravity has a greater force on denser liquids and so today we're gonna take a closer look at the density of these two mixtures. Now to do that, I've poured out an equal volume of both chocolate cake batter and flan mixture. Now which one starts off on the bottom is gonna depend on density, and for that, I'm gonna take the mass. You can see that the mass of the chocolate cake batter is slightly more than the flan mixture, but only by a little bit, the chocolate cake is a little over 81 grams and the flan mixture is a little under 80 grams. Now that's pretty close, I have to say, and depending on your recipe, your flan mixture might actually have more mass than the same volume of cake batter. Whichever one has more mass is more dense. The force of gravity pulls harder on things that are more dense and I'm going to layer my chocolate cake batter right at the bottom. I've covered the bottom of this container with some caramel so that my flan comes out with a nice, brown topping, but I'm gonna first pour in my chocolate cake better. Make sure I get it all out. And then I'm gonna slowly pour my flan mixture on top. And you can see that my flan mixture sits on top, but maybe your recipe is a little different and your flan mixture maybe has a little more sugar. It might sink right to the bottom, so that's how you know your flan mixture is more dense. It'll feel a little less magical, but it'll still taste delicious. So my chocolate flan is assembled, I'm gonna put it into a water bath and then stick it into an oven for 30 minutes and we'll see what happens. Our chocolate flan is done, let's take a look. Okay, you can see that the chocolate cake layer baked out on top and the flan layer is now on the bottom. It's nice to actually chill this for a little bit before you eat it, so that the flan sets up. So I'm gonna save that and put it in the fridge later. And I have one here that I actually made earlier and chilled, and you can see also that it stayed set up the flan is on the bottom and the chocolate cake is now on the top. But we need to get it out of here, so I'm gonna loosen it up, just by going around with a knife and then, flipped over in the oven, so I'm gonna flip it over one more time. You can see, oh, look at that beautiful chocolate flan. You can see now very clearly you have the two layers. I'm actually gonna cut into this to get a better look, at the two layers. And you'll notice that the layer of flan is much thinner than the layer of cake. And remember we went in with the same volume of liquids, but the cake baked up much taller. That means its volume increased. So the same mass of cake now has a greater volume, which means its density decreases. Now again, as it's cooking, gravity is just pulling on both of these liquids and as the density of the cake decreases, there's a moment where the density of the flan mixture is higher and so all of a sudden gravity will pull it underneath and that's how it magically inverts in the oven. You'll also notice that this layer of flan is, is now much smaller, it looks like there's less flan compared to cake. So if you want them to be equal, you probably wanna start out with a greater volume of flan than cake batter. I think my mom would like that. So thanks to gravity and density, you can bake up a sweet treat sure to please every single member of your family.