Brewer's spent grain (also called Spent grain, Brewer's grain or Draff) is a byproduct of beer brewing consisting of the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process.[1] It consists primarily of grain husks, pericarp, and fragments of endosperm.[2] By mass, spent grains consist of about half carbohydrates, and the rest being mostly proteins and lignin. Carbohydrates include traces of starch, cellulose, β-Glucans, and arabinoxylans.[2] Spent grain is considered to be a good source of un-degradable protein and water-soluble vitamins in animal feed.[3] It is quite palatable and is readily consumed by animals.[3] Spent grains can also be used as fertilizer, whole grains in bread,[4] as well as in the production of biogas. Spent grain is also an ideal medium for growing mushrooms, such as shiitake, and already some breweries are either growing their own mushrooms or supplying spent grain to mushroom farms.[5]. This, in turn, makes the grain more digestible by livestock.[6]