Both bleached and unbleached flour are made from wheat flour that has been stripped of its bran and germ. Both types of flour are widely available and cost about the same. For most purposes, regular, unbleached flour is the best choice. Reach for bleached flour when making delicate cakes, piecrusts or biscuits.
How They're Made
After all-purpose flour is milled, it naturally oxidizes over several weeks to an off-white color. Bleached flour undergoes an additional whitening step. Millers use chlorine gas, chlorine dioxide or benzoyl peroxide to bleach flour. Some millers use potassium bromate as a whitening agent. This chemical has been banned in many countries as a carcinogen, although it is legal to use in the United States.
How They Perform
Bleached flour has less protein than unbleached flour, so baked goods made with it are tenderer. Bleached flour also absorbs moisture more quickly. Although you probably won't notice the difference in a batch of cookies or muffins, you will notice it in a light, tender cake. This is why cake flour is usually bleached. Use unbleached flour for yeast breads, cookies and puff pastries. Reach for bleached flour when you're making a cake with a fine crumb. Piecrust and biscuits also benefit from bleached flour. If you don't have bleached flour, substitute a few tablespoons of cornstarch for some of the flour.
How They Look
The most obvious differences between bleached and unbleached flour lie in their appearance. Compare the two side by side, and you'll notice that bleached flour is bright white, while unbleached flour has a softer, more natural appearance. You won't notice the difference in most baked goods, although white cakes and angel food cakes appear brighter when made with bleached flour.
How They Taste
Bleached flour has a slightly bitter aftertaste that may be detectable in delicate cakes with subtle flavors. You probably won't notice the taste in breads or cookies, although some people are extra sensitive to it. From a nutrition standpoint, unbleached flour is a better choice, because it's free of the whitening agents used in bleached flour.