Why do you put SR flour in cakes?

You're likely thinking of cake flour, not "SR flour". SR stands for "self-rising", and it's a type of flour that already has baking powder and salt added to it.

Cake flour is a low-protein flour that's specifically designed for making cakes. It has a lower protein content than all-purpose flour, which means it produces a cake that is:

* More tender and delicate: The lower protein content results in less gluten development, making the cake softer and less chewy.

* Lighter and airier: The fine texture of cake flour helps create a lighter, more delicate crumb.

* More evenly textured: The low gluten content prevents the cake from becoming tough or rubbery.

Why not use all-purpose flour for cakes?

While you can use all-purpose flour for cakes, the result may not be as desirable. The higher protein content in all-purpose flour will lead to a denser, chewier cake.

In summary: Cake flour is preferred for cakes because it produces a more tender, airy, and delicate result. It's worth investing in if you bake cakes often.