Brewery spent grains can be fed to cattle, hogs, poultry, or fish. As they are ruminants, cattle are able to utilize a good portion of the nutrients from brewery spent grains, and it is what most farmers use them for. However, spent grains are not nutritionally complete and should not be relied on as the only feed source.
When still wet, spent grains are initially between 77 and 81 percent water by weight. The remaining solid matter is comprised of fiber, protein and other associated organic matter. The fiber includes the husk, pericarp, and seed coat of the malted barley grains. The fibrous husk material constitutes about 70 percent of the dry weight of brewery spent grains. During mashing, the starchy interior of the grain has been dissolved and rinsed away.
The fiber is digestible by ruminants, and most spent grain is used to feed cattle. However, brewery spent grains can be fed to poultry if enzymes are added to help degrade the fiber to make them digestible.
Between 20 and 30 percent of the dry weight of brewery spent grains is protein, and 36 percent of this is rumen degradable in cattle. Although some soluble protein is leached and drained during the brewing process, insoluble proteins and some residual soluble proteins remain. A small amount of simple sugar, mostly maltose, remains in spent grain, along with 7 to 10 percent crude fat.
Spent grain contains a lot of minor components that are nutritionally important, including essential amino acids and non-essential amino acids. When supplemented with an outside nitrogen source (such as urea), brewery spent grains can provide all the amino acids cattle require.
Spent grains also contain a wealth of vitamins and minerals. Cattle require more calcium than spent grains supply, so some supplemental calcium is required if spent grains are used as a significant proportion of the cattle’s feed. If not supplemented, growth rate could be slowed.
Some have even examined the possibility of incorporating spent grains into human diets, specifically via cookies. The authors of the study found that spent grains are rich in hydroxycinnamic acid and phenolic acids, which may have anti-oxidant, anti-inflammatory, and anti-cancer properties.
Brewery spent grains contain 71 to 75 percent total digestible nutrients (TDN). For comparison, corn feed yields 88 to 90 percent TDN. Given that brewery spent grains are often free, or obtained at a cost far below normal animal feed, they are an attractive source of nutrition for livestock producers.
Some studies have shown benefits beyond cattle. Carp fish whose diets were supplemented with spent grains showed faster weight gain than carp fed their regular diet. In dairy cattle, supplementary spent grains increased milk yield, milkfat percentage, and the amount of milk solids. In correct proportion to their normal feed, cows increased their feed intake, experienced quicker weight gain, and achieved higher body weight. Part of the increase in feed intake may be due to the water in the grains. In general, animals tend to prefer food with some moisture content to dry feed.
The effects of spent grain consumption as hog feed are not quite as impressive. In hogs, increased amounts of dried spent grains correlated with lower feed intake and a longer time to reach slaughter weight. As hogs are not ruminants, and can’t digest fiber very well, the primary value of spent grains in their diet is the protein content.
A drawback to brewery spent grains is that they must be used quickly or they will go bad and lose their nutritional value. They will begin to smell after only a day of warm weather. As such, they should be used within a few days of pickup. Drying the grains to below 12 percent moisture will help slow their spoilage. However, this is usually done in rotating drum devices, and can be costly compared the value of the grain.
On the plus side, most breweries brew every day, or almost so. If you find a brewery willing to work with you, you will have a steady supply of the material. Some farmers have extended the usefulness of spent grains by preserving them with benzoic acid, formic acid, or potassium sorbate. In one case, applying 30 percent beet molasses with 0.3 percent potassium sorbate worked well to preserve wet spent grains, so long as they were held in plastic bags with minimal headspace. Spent grains are usually stored in plastic bags, sealed to keep out as much oxygen as possible. Leaving bags open contributes to mold growth and decreased palatability.