Cake Flour

Cake flour — also sold as pastry flour when milled a touch stronger — is low-protein white wheat flour prized for tender, fine-crumbed cakes. It is the same milled endosperm as ordinary all-purpose flour, but ground from softer, lower-protein wheat and milled far finer, so it carries only about 6 to 8 percent protein against all-purpose's 9 to 11.5 percent. That low protein is the whole point: hydrated and mixed, it forms little gluten, so a batter stays weak and extensible and bakes into a soft, delicate crumb instead of a chewy one. In North America cake flour is also usually chlorinated — bleached with chlorine gas, which whitens it, subtly damages the starch and lowers its pH, letting it hold more sugar and liquid and set a taller, finer sponge. On its own it is bland and faintly sweet, smelling only of dry cereal with a soft, powdery, almost silky feel — its magic, like all baking flour, is structural, not aromatic.