I've heard various rumors suggesting that using unbleached [wheat] flour is better than bleached [wheat] flour when baking (cakes, squares, cookies...). Is this true? If so, why?
Good Answer Hobodave....tacking onto that:
Most southern U.S. brands (White Lily, Martha White) of all-purpose flour are bleached because southerners tend to make more quick breads (biscuits, cornbread, hoecakes, pancakes, as well as cakes, pie crusts, cobblers) where tenderness is desired. White Lily has just started producing unbleached all-purpose flour as well.
Brands from the Northeast (King Arthur) and midwest are usually unbleached because those regions tend to make more yeast breads and the additional gluten forming capability of unbleached flour produces better results.
National U.S. brands (Pillsbury/Gold Medal) often produce both types or stick with unbleached.
Cake flour is always bleached (usually chlorine gas).
More information on differences in types of flour can be found in my article titled "Flour Power"
Freshly ground wheat is yellow. The all-purpose flour we buy in stores is all bleached, either naturally (unbleached) or chemically (bleached).
Unbleached flour is whitened by natural oxidation, though it still retains a slight golden hue. This takes months, and thus it commands a higher price.
Bleached flour is whitened using a combination of some particularly nasty chemicals, including benzoyl peroxide, chloride gas, and chlorine dioxide. Additionally potassium bromate is usually added. Many countries in Europe ban bleached flour as a whole due to safety concerns. Potassium bromate is a known carcinogen and is banned in many countries throughout the world as well.
That said, the two are nearly identical in nutritional value and can be used interchangeably. The major difference is in consistency. Unbleached flour has more gluten and is thus sturdier and good for yeast breads and other stout baked goods. Bleached flour results in a lighter softer finished good.