Bread Flour and Cake Flour Are Not the Same
Walk down the baking aisle of a grocery store and you will see several bags of white flour. One says bread flour, another says cake flour, and a third says all-purpose. They may look alike, but a baker will tell you that they behave quite differently. The reason is protein.
All wheat flour is made by grinding wheat kernels. Wheat holds proteins that join together when flour is mixed with water. Kneading, which means pressing and folding dough, helps those proteins link up into a stretchy web called gluten. Gluten acts a little like a net of rubber bands, and it traps the gas made by yeast, so the dough can rise.
Bread flour has more protein than the others. Its dough makes lots of gluten, which gives bread a strong, chewy texture and lets loaves puff up tall. Cake flour is the opposite. It has less protein, so it forms only a weak web, and the cake turns out soft and tender. All-purpose flour sits in the middle, which makes it a handy choice for cookies, pancakes and many other recipes.
Bakers also change how much they mix. A pie crust or muffin batter is handled gently, so that gluten does not get too strong. A loaf of bread is kneaded for a long time to make plenty. Picking the right flour and the right amount of mixing helps every recipe come out well.