is a layer of living endosperm cells that encloses the outer surface of the starchy endosperms of cereal grains. It is the major enzyme source of malted barley. In barley, this layer is about three cells thick and can be colorless or blue in color. In wheat, rice, maize, rye, millet, and sorghum the aleurone layer is one cell thick. Aleurone cells of barley contain storage lipids, phytin, proteins, and sucrose. The aleurone layer is covered by the testa, pericarp, and husk. Together, the aleurone layer, pericarp, and testa are the major tissues of cereal bran. The primary function of the viable aleurone layer during malting is to produce a wide range of hydrolytic enzymes that contribute to the degradation (modification) of the starchy endosperm. During malting, the germinated embryo produces and secretes gibberellic acid into the adjoining aleurone layer. Gibberellic acid travels along the aleurone layer, inducing it to produce endosperm-degrading enzymes that not only modify the endosperm during malting but also act during mashing to optimize the development of sugars. Enzyme production includes the synthesis of enzymes such as alpha-amylase, endo-beta-glucanses, limit dextrinase and endoproteases, and the activation of enzymes such as beta-amylase and carboxypeptidase, which are located in the starchy endosperm. The phytin of the aleurone layer helps to control wort pH. Foam-stabilizing proteins such as lipid transport protein are derived from the aleurone.

See also germination, malting.