Protein, you ask? Yes, protein! It's like the gym rat of the flour world - it makes your baked goods all tough and chewy. And trust me, you don't want a tough cake, that's just a recipe for disaster. All-purpose flour, on the other hand, has a higher protein content, making it better suited for bread and other heartier baked goods.
Now, I know what you're thinking, "Can't I just use all-purpose flour and hope for the best?" Well, let me tell you, hope is not a baking strategy, my friend. If you use all-purpose flour in a cake recipe, you might end up with a cake that's as dense as a brick. And not the good kind of brick, like a beautifully crafted brick oven, but the bad kind, like a brick that you use to build a wall.
But, if you're in a pinch and you don't have any cake flour on hand, you can try making a substitution. To do this, you'll need to take out some of the protein from the all-purpose flour, which you can do by removing a small amount of flour and replacing it with cornstarch. It's like a little flour hack, and it might just save your cake from certain doom.
Cake Flour vs. Regular Flour | Cake Flour 101