Bran refers to the outer hard layers of a cereal grain, specifically the combined aleurone and pericarp that surround the endosperm. In the case of corn (maize) bran, the pedicel is also included in this component. It serves as an integral part of whole grains alongside the germ.
While highly nutritious, bran contains a high fiber content that can make it difficult to digest. Additionally, its high fat content makes it prone to becoming rancid, which reduces its shelf life. Consequently, bran is typically removed from whole grains during refining processes, such as when processing wheat into white flour or brown rice into white rice.