Bran is the hard outer layer of grains like wheat, rice, or oats that gets removed during milling to make white flour. Think of it like the protective shell around the softer inside part of the grain. When wheat is ground into flour at a mill, the bran gets separated out and often sold separately because it's packed with fiber and nutrients.

You've probably eaten bran without realizing it. Whole wheat bread contains bran, which is why it has that slightly nutty flavor and brown color compared to white bread. Some cereals, like bran flakes or raisin bran, use wheat bran as a main ingredient. The tiny flakes in these cereals are pieces of that outer grain layer.

For most of human history, people ate their grains with the bran still attached because removing it took extra work. But when industrial milling made it easy to remove bran in the 1800s, white flour became popular because it made lighter, fluffier bread. Today, many people specifically seek out bran because nutritionists recognize that the fiber and vitamins in that outer layer are valuable for digestion and health.