Yea, I'm gonna spill some secrets on my blog. Not all of them, of course, but some. Like the secrets to moist, yet firm-enough-to-stack cakes. It's all about understanding gluten. Sounds really boring, kind of like a chemistry class. But I promise - if you "get" gluten, you "get" baking. Seriously. So it's worth learning.
I also promise that the word "gluten" will be repeated in this blog post more times than you care to count. There, you have been warned.
Essentially, gluten is the sticky stuff that happens when wheat flour meets water. The proteins in the wheat flour, glutenin and gliadin will combine, and create, you got it, glue. So by adding more (or less) water, you'll control the texture of your dough or batter. So far, so good, right? So, when you add some kind of leavening ingredient, whether it's baking soda, baking powder or yeast, it will rise. The cake heats, and the baking soda turns in to carbon dioxide, and pretty much creates little air bubbles. Think of the air bubbles like they're inflating a balloon, and your gluten is the exterior, the rubber part. That's why it's crucial that the balloon is made of the right material for the occasion, so that it won't pop or deflate.
So, when baking, the first thing to do is to make sure we have the right kind of flour, as different flour types have different protein content. When baking cakes, we want cake flour, which has a relatively low protein content, usually around 8%. All purpose flour is ok, too, with a protein content at around 10%. Stay away from bread flour which can have as much protein as 15% and would make for a really dough-y, tough and gross cake. Why is this? Because less protein means weaker gluten, and more tender cakes.
Then comes the more complicated part- understanding how other ingredients and circumstances affect the gluten. Basically, fats, egg yolks and sugar break down gluten. Salt helps it. Water creates it, but after drenching the flour the first time, it will in turn start to break it down. (Yikes! Am I making it complicated enough yet?)
Which means that if you add the fat to your recipe before the water, very little gluten will form at all, since the fat will coat the flour and make it water resistant, like when you make a pie crust. In a cake you'll want to create gluten in order to make your cake fluffy, but not so much that it turns tough and rubbery. Which is why you'll want to add your water first, then your fat, then your sugar. In a really sweet cake, you'll want to add the tiniest pinch of salt.
I'm gonna make this even more complicated now: Working the dough affects your batter a whole lot too. Mixing and stirring will strengthen your gluten, so overmixing may ruin your cake and make it chewy and rubbery. If you were making a yeast dough, you'd want to handle your dough as much as you could - because you'd need a sturdy dough. Not in this case.
So, by now you've gotten the right flour, measured your ingredients correctly, added them in the right order and mixed it just right. Are we safe yet?
Not quite. Another crucial part still remains: Cooling.
When your cake is hot, the gluten is still fragile. This is why, if you take your cake out of the pan too soon, or try to cut it too soon, it will fall apart or just get flat. The cake needs to cool for a few minutes in the pan so it will get a little bit stronger, then hang out on a wire rack until it's completely cool. Completely. I'm not kidding. Have lots of patience even if it smells awesome.
Even when the cake is completely cool, there's still physics and chemistry going on inside your cake. That's why I never cover a cake in fondant until 24 hours after I bake it, because the next day it may have settled a little bit. Not so much you could see it, but enough that the fondant could have become uneven and ugly. And nobody likes ugly. We like "homemade" and "charming", but not ugly.
And thats, pretty much, that.