Wheat is a grass whose fruit, the grain or kernel, contains one seed. The endosperm and embryo of the wheat plant are surrounded by the pericarp, or fruit wall, and the remains of the seed coat. More than 80 percent of the volume of the wheat kernel is made up of the starchy endosperm, and white flour is made by milling this starchy endosperm.

Wheat bran constitutes approximately 14 percent of the wheat kernel and is found in the covering layers and the outermost layer of the kernel. (It is the embryo of the wheat plant and represents approximately 3 percent of the wheat kernel.) Although nearly two dozen species of wheat exist, the most important ones for commercial use are common wheat (Triticum aestivum, sometimes referred to as Triticum vulgare) and durum wheat (Triticum durum). The varieties of common wheat account for 90 percent of the wheat grown worldwide. Durum wheat accounts for 5 to 7 percent of the wheat grown, and all other species account for the remainder of the wheat grown.