Spent Grain is the compact waste of malt and/or grains left after mashing and lautering in the brew house. It weighs approximately 100–130 kg wet for every 100 kg of dry grist that went into the original mash. Spent grain consists primarily of barley husks (the aleurone and pericarp layers), embryonic remnants, protein, and minerals. When dried, it typically contains approximately 28% protein, 8.2% fat, 41% carbohydrates, 17.5% cellulose, and 5.3% minerals. When wet, water by mass comprises 75%–80%. What is waste to the brewer is valuable to the farmer; because of its many nutrients, spent grain is an excellent animal feed, and most livestock find it highly palatable when it is fresh. Once the spent grain cools, however, it must be processed quickly or it will spoil. Breweries traditionally dispose of it while it is still damp, collecting it in a silo or other container for local farmers or distributors. It is of special value for ruminants (mammals such as cows that partially digest food by chewing a cud) because it better withstands protein degradation in the rumen (a chamber for microbial fermentation of ingested feed) when compared to other feeds. Spent grain is also well suited for silaging (a method of fermenting and storing cattle fodder). No additives are necessary and it yields a high-quality silage with an optimal pH value and minimal protein breakdown. Spent grain can also be dried and then stored or burned as an alternate energy source, or it can be fermented to produce biogas (the generic term for gas produced by the biological breakdown of organic matter in the absence of oxygen). It also is a good additive to compost, and it is widely used as a medium on which to grow mushrooms. Samples of spent grain are often analyzed in the lab to provide quantitative feedback on brewhouse performance. In many small breweries and brewpubs, “digging out the mash tun” is a vigorous daily ritual carried out with a shovel, a welcome portent to the end of the workday.