Among grains, wheat flour is unique because it has the potential to produce gluten, a protein that imparts strength and elasticity to dough and influences the texture of baked goods. The gluten content of flour depends on whether the flour is made from hard or soft wheat; hard wheats are higher in protein than soft wheats, and thus produce more gluten. Most flour is a mixture of hard and soft wheat.
Because the production of flour isn’t standardized, flours from two manufacturers may use different milling procedures and consist of different blends, which will produce varying results in the kitchen. For example, all-purpose flours sold in the southern region of the United States contain a higher proportion of soft wheat, good for making the light, airy biscuits that are popular there. In northern states, by contrast, the preference is for breads rather than biscuits, and the all-purpose flour used in breadmaking contains a higher proportion of hard wheats.