Bleached flour is processed with a chemical called chlorine bleach. The flour can be treated with benzoyl peroxide or hydrogen peroxide. The bleaching process makes the flour whiter, so it doesn’t turn brown when exposed to air. Unbleached flour is not chemically treated and remains a light yellow color. Cake flour has been bleached with chlorine but also sifted more finely than all-purpose or bread flour. Cake flour is finely ground and comes bleached or unbleached but has an added ingredient to make cakes less dense. It also has the lowest amount of protein out of all the flours. Less protein is believed the yield a lighter and tender product.