Why do I even need cake flour? you may be asking yourself. Well, let me tell you, it seems totally unnecessary at first glance, but at times can be the only thing separating you from a truly tender cake. The primary difference between flours is their protein content; protein (aka gluten) is what gives breads and cakes their structure. Gluten is in a sense the keystone in our baking architecture. It holds the weight and gives structural integrity to whatever we’re baking. So it follows that to get the dense chewy structure of bread you would want a flour with a lot of protein. Whereas to get the light airy texture generally equated with cake you would want much less.
So if you find yourself faced with a recipe that calls for cake flour, before ignoring the directions, know that there’s another way. An easy substitution that will allow you to never have to buy cake flour, but never be without it again.
-Start by measuring out 1 cup of All-Purpose Flour. Remove 2 Tablespoons of the flour, sending it back from whence it came. Replace those 2 Tablespoons of all-purpose flour with cornstarch.
-Now for the tedious, albeit necessary step of sifting the flour 4 times. 4 TIMES??!
That’s right, as we are making substitutions here, it is of the utmost importance that we thoroughly combine the cornstarch with the flour to make one unified front in the battle against gluten development. You see, by replacing some of the flour with cornstarch we are replacing some of the gluten with a tenderizing element. The cornstarch along with any fats and sugars in the recipe inhibit gluten development. The fats effectively coat the strands of gluten preventing that really solid structure we expect in bread, and the sugar and cornstarch drink up part of the liquids in the recipe preventing even more of the gluten development.
Starches like potato and arrowroot can also be used but are touchy. Cakes with these starches will cook more quickly and remain moist longer.
Just as you can make your own cake flour, you can also make a passable bread flour by adding a few tablespoons of vital wheat gluten to good old reliable all-purpose Flour. However, I don’t know how much more likely it is for the average layman to have vital wheat gluten lurking in the back of his fridge as opposed to a box of bread flour.