Bleached vs. unbleached flour

What's the difference between bleached and unbleached flour?
- Virginia Dyson, Central Islip

When flour is milled, it has a yellowish cast. Left on its own for a few weeks, it naturally whitens to a warm off-white. This is so-called unbleached flour. Bleached flour has been chemically lightened (with either benzoyl peroxide or chlorine, both ruled safe by the FDA) to achieve a brighter white. Bleaching flour slightly diminishes the protein content so it is less useful in bread doughs, where proteins form the gluten that lends bread its structure. However, bleached flour can be desirable when making delicate cakes and pastries and, in fact, most cake and pastry flours are bleached. For general all-purpose flour, unbleached is your best bet.