Difference between all purpose and cake flour? Can they be substituted for each other? Why or why not?
AP flour has about 11% protein, and cake flour is 6-8%. Using cake flour makes the cake lighter, but a lot of cakes can stand up to AP flour. (Remember that in olden days, there was a cake on the table almost every night and the measurements were regular cups and spoons.) Here's some info about substituting if that's what you're looking for:
To elaborate upon the previous response, cake flour makes the cake lighter, but also makes it less "tough." The gluten (or protein) in flour is what gives baked goods structure. You want high protein flour for bread or pizza, for instance, because you want them to have a solid structure or chewiness. Cakes, on the other hand, should be tender, with just enough structure to hold together, but not so much that they are tough. Cake flour helps with that.
I hate cake flour. I find it gives cakes some sort of metallic after taste. I bake all the time and I always and successfully so replace cake flour using this formula. 1 cup cake flour = 3/4 cup (12 tbsp) all purpose flour + 2 tbsp cornstarch. It makes the cake as light as if cake flour was used but without the metallic after taste. Trust me on this. Try a recipe twice, once with the cake flour and once with my formula, and see what u like best.
Aside from the technical aspects (protein, gluten), there's subjective taste & how much space you have for baking goods. Perhaps do a blind taste test of well-love recipe, using both flours and see whether you & yours find that cake flour version tastes better enough to give the cake flour space.