Bleached flour

Under the U.S. standard of identity, flour is the food prepared by grinding and bolting cleaned wheat. The same regulation permits optional bleaching agents, such as nitrogen oxides or chlorine, in amounts no greater than needed for bleaching, and requires that the label bear the word bleached when one is used.

Freshly milled flour is slightly yellow. Bleaching whitens it and alters its behavior, giving finer, softer crumb in cakes and a bright white color, which is why chlorinated flour is often chosen for layer cakes, cookies and pastries.

Bleached flour can usually be swapped for unbleached in most recipes, though cakes may rise and brown a little differently and bread flour is often left unbleached.