All of the recipes posted on my blog use all-purpose flour unless specified in the ingredient list. Baked goods, however, sometimes call for the use of cake flour. I thought I would explain the difference between the two.
Cake flour is used in recipes where a fine, tender crumb is desired, such as in a layer cake. For many cakes, where the batter is stirred, all-purpose flour is suitable. These cakes won't be as fine textured, but they will still be tender and moist.
Made from soft wheat, cake flour contains about 8 to 10% protein. All-purpose flour is made from hard wheat and contains about 10 to 12% protein. Flour with a lower percentage of protein results in a cake that has a delicate tender crumb.
Cake flour is also more finely ground and has undergone a bleaching process so it will produce a cake with a finer crumb than all-purpose flour.
I have experimented with substituting one for the other in recipes and have found this to be completely true. Typically, I will use cake flour for layer cakes such as devils food, yellow, or white. Carrot, banana, and spice cakes do best with all-purpose flour.