Naturally vs. Artificially Bleached

• At bottom all white flours are bleached, in one fashion or another. Freshly ground flour makes dense loaves that don't rise well, so for centuries millers aged their flour. As it aged, and was transferred between storage bins, exposure to oxygen gradually whitened the flour and improved its baking qualities. The development of modern high-speed milling in the late 19th century made that natural bleaching process unwieldy, and millers quickly discovered that chemical bleaching could achieve the same purpose in a fraction of the time.

Bleaching Processes

• During most of the 20th century, all-purpose flours in the U.S. were bleached with a chemical called potassium bromate, but that substance is now little-used because of potential health concerns. Most flour is now bleached with either ascorbic acid or a form of peroxide. Ascorbic acid -- better known as vitamin C -- is also a potent antioxidant, and can slow the development of off-flavors in the flour. Cake flour is bleached through a harsher chlorine process, which makes it both extra-white and more porous. Unbleached cake flour is available, but doesn't give cakes the exceptional delicacy of bleached cake flour.

The Differences

• For general purpose baking, there's little reason to favor unbleached over bleached flour. Some bread enthusiasts feel that unbleached flour makes slightly better or more flavorful bread when it's given a long, slow rise, but the differences are subtle. More often, when unbleached flour is specified, it's only because the baker who created the recipe is health-conscious and opted for less-processed unbleached flour. Bleached flour produces baked goods with a lighter and cleaner color, while unbleached flour gives baked goods a slightly creamy, off-white tint.

Other Factors

• As a rule, the difference between bleached and unbleached flour is less visible in your baked goods than other factors. Each brand and grade of flour uses a different blend of wheats, hard or soft and red or white. These wheats all have different baking characteristics, so you'll see more variation between brands than between bleached and unbleached in the same brand. All-purpose flour can also vary sharply in its gluten content from region to region, so if you're having difficulty with your recipes you might consider using bread flour for yeast doughs or pastry or cake flour for your other baking. Once you've found a flour that works well for you, stick with it until you've gained enough experience to recognize and adapt to the vagaries of other brands.