Wheat flour is by far the most common in the United States, but nearly any grain can be made into flour. Even seeds and legumes can be finely ground this way. No matter the variety, flour is generally available in several forms.
Bleached, all-purpose flour
This is a blend of high-gluten hard wheat and low-gluten soft wheat, which makes it suitable for all baking and cooking needs. Self-rising all-purpose flour includes baking soda and salt. Bleaching is often done chemically; it also occurs naturally as flour ages.
Refined flour, refined white flour
Refined flour is flour from which the nutritious (and more perishable) bran and germ layers have been removed.
Fortified flour refers to an all-purpose flour, usually wheat, to which nutrients like thiamine, riboflavin, and niacin, removed during refining, have been added back.
This is a whole wheat flour that has had about 80 percent of its bran sifted off. It may also be called "unbleached flour" or "reduced bran flour."
In this milling process high-velocity steel hammerheads are used to powder whole grains at ultra-high speed. The method generates a great deal of heat and can destroy nutrients.
In this milling process steel rollers or cylinders are used to grind grains at high speed. A great deal of heat is generated, causing nutrients to be destroyed.
Stone-milled (stone-ground) flour
This milling process employs a pair of ridged stones to crush and grind grains slowly, without creating heat that can destroy nutrients. The ground flour is sifted to catch larger particles of bran and germ, which are then ground again and mixed with the rest of the flour to produce a more nutritious flour.