Whole wheat flours contain all three major parts of the wheat kernel,
- Bran is the hard, brownish outer protective skin of the grain. It surrounds germ and the endosperm, protecting the grain from weather, insects, mold, and bacteria.
- The bran consists of 7 layers. The bran layers are a concentrated source of dietary fiber.
- The aleurone layer is the largest portion of the bran, constituting 75% or more of its dry weight.
- The aleurone layer is a concentrated source of vitamins, minerals and other nutrients.
- The endosperm is the inner part of the grain. It supplies food to the growing seedling.
- The main nutrients in the endosperm are protein and carbohydrate. About 50 to 75% of the endosperm is starch. It also contains storage proteins, typically 8 to 18%. Relatively few vitamins, minerals, fiber, or phytochemicals are found in the endosperm.
- White flour is produced from the endosperm.
- The germ contains the plant embryo. It typically accounts for about 2 to 3% of the wheat's dry weight.
- Most of the wheat kernel's fat and vitamin E content is found in the germ.