Harold McGee

Grain Structure and Composition

Appears in
On Food and Cooking
On Food and Cooking

By Harold McGee

Published 2004

  • About
The edible portion of the cereal plant, commonly called the grain or kernel, is technically a complete fruit whose ovary-derived layer is very thin and dry. Three of the cereals—barley, oats, and rice—bear fruits that are covered by small, tough, leaf-like structures that fuse to form the husk or hull. Bread and durum wheats, rye, and maize bear naked fruits and don’t have to be husked before milling.

All the grains have the same basic structure. The fruit tissue consists of a layer of epidermis and several thin inner layers, including the ovary wall; altogether, it’s only a few cells thick. Just underneath the seed coat is the aleurone layer, only one to four cells thick and yet containing oil, minerals, protein, vitamins, enzymes, and flavor out of proportion to its size. The aleurone layer is the outer layer and only living part of the endosperm; the rest is a mass of dead cells that stores most of the carbohydrates and protein, and that takes up most of the grain’s volume. Abutting onto the endosperm from one side is the scutellum, a single modified leaf that absorbs, digests, and conducts food from the endosperm to the embryo, or “germ,” which is at the base of the fruit, and which is also well endowed with oil, enzymes, and flavor.