By Harold McGee
Though manufacturers and professional bakers can obtain flours from particular wheats, most flours for sale in supermarkets are labeled according to their intended use, with no direct indication of the kind of wheat or wheats they contain—they’re usually a blend—or their protein content or quality. Flour compositions can vary significantly from region to region; “all-purpose” flour in much of the United States and Canada has a higher protein content than “all-purpose” flours in the South or Pacific Northwest. Not surprisingly, recipes developed with a particular flour often turn out very differently when made with another, unless care is taken to find a replacement that closely approximates the original. The box lists the compositions of common wheat flours.