What are you, a shameless shill for People for the Ethical Treatment of Food Products? Because you just lobbed us one heck of a softball in the hardball world of answering cooking questions.

Flour is bleached for two reasons: 1. to whiten it more quickly than occurs naturally, and, 2. in the case of cake flour, to produce a stronger starch network and to help the fat in a recipe disperse more evenly throughout the batter. Either function can apparently be accomplished without the use of a bleaching agent, but some millers just won't listen. And why should they, when the US Food and Drug Administration and even the World Health Organization find bleaching to be safe? (The European Union does not agree, though, so bleached flours may not be sold in Europe.)

Beyond their chemical processing, bleached and unbleached flour are absolutely interchangeable. One cup of bleached flour equals one cup of unbleached flour.