All-purpose flour is a blend of high-gluten hard wheat and low-gluten soft wheat. It’s a fine-textured flour milled from the inner part of the wheat kernel and contains neither the germ (the sprouting part) nor the bran (the outer coating). U.S. law requires that all flours without wheat germ must have niacin, riboflavin, thiamin and iron added. (Individual millers sometimes also add vitamins A and D.)
These flours are labeled “enriched.” All-purpose flour comes in two forms–bleached and unbleached–that can be used interchangeably. Flour is bleached naturally, as it ages, or chemically. Most flour today is presifted, requiring only that it be stirred, then spooned into a measuring cup and leveled off.
Bread flour is an unbleached, specially formulated, high-gluten blend of 99.8 percent hard-wheat flour, some malted barley flour (to improve yeast activity) and vitamin C or potassium bromate (to increase the gluten’s elasticity and the dough’s gas retention). It is ideal for yeast breads. The fuller-flavored whole-wheat flour contains wheat germ and has a higher fiber, nutritional and fat content. Store in the refrigerator to prevent rancidity.
Cake or pastry flour is a fine-textured, soft-wheat flour with a high starch content. It makes particularly tender cakes and pastries. Self-rising flour is an all-purpose flour with baking powder and salt added. It can be substituted for all-purpose flour in yeast breads by omitting the salt and in quick breads by omitting both baking powder and salt.
Substitution: FLOUR (for thickening) 2 Tbsp all-purpose = 1 Tbsp cornstarch, potato starch or rice starch OR 4 tsp arrowroot OR 2 Tbsp quick-cooking tapioca
FLOUR 1 cup sifted all-purpose = 1 cup minus 2 Tbsp unsifted all-purpose flour
FLOUR 1 cup sifted cake = 1 cup minus 2 Tbsp sifted all-purpose flour
FLOUR 1 cup sifted self-rising = 1 cup sifted all-purpose flour plus 1 1/2 tsp baking powder and 1/8 tsp salt
from The New Food Lover’s Companion, Second Edition, by Sharon Tyler Herbst