All-Purpose Flour

All-purpose flour (often abbreviated as AP flour) is the workhorse of the home kitchen. It is milled from a blend of hard and soft wheat varieties, resulting in a moderate protein content that typically ranges between 10% and 12%. This protein range determines gluten development: when mixed with water, the proteins glutenin and gliadin bond to form a gluten network that gives structure and elasticity to doughs and batters. The medium protein level makes AP flour highly versatile: it has enough protein to build structure in rustic breads and chewy cookies, yet low enough to prevent cakes and pie crusts from becoming tough.

In the US, AP flour is available in bleached and unbleached varieties. Bleached flour is treated with chemicals like chlorine gas to speed up aging, resulting in a whiter color, finer grain, and slightly lower protein behavior, which is ideal for tender cakes. Unbleached flour ages naturally in the air, retaining a slightly off-white color and stronger gluten structure, which is preferred for yeast breads and puff pastry. When substituting all-purpose flour for specialty flours, adjustments to liquid ratios are often necessary because AP flour absorbs moisture differently than high-protein bread flour or low-protein cake flour.