After a big brew day, brewers can often end up with mountains of spent grain, with the product making up 85% of a breweries waste material. The high fibre content (~70%) of the used grain makes it difficult for humans to digest and, unlike Will Tatchell from Van Dieman Brewing, most brewers don't brew on a working farm, allowing them to just feed the leftover grain to their livestock.
However, scientists have recently found a new way to extract the protein and fibre from spent grain to create new types of protein sources and biofuels. The results were recently presented at the American Chemical Society (ACS) spring meeting by researchers Haibo Huang and Yanhong He from Virginia Tech.
"Spent grain has a very high percentage of protein compared to other agricultural waste, so our goal was to find a novel way to extract and use it," said Yanhong He.
The process begins by separating the protein from the fibre using a novel wet fractionation (separation) process through the addition of the commercially available enzyme, alcalase. Alcacase is commonly found in detergents and is the hard-working enzyme that removes protein stains like grass, blood, or egg. It works by breaking the peptide bonds (chemical bonds between individual amino acids) to release the amino acids away from the fibre in the grain. After this, the product is sieved leaving a protein concentrate and fibre-rich product. While the protein concentrate has been proposed as a more sustainable replacement for fish meal or as an alternative meat-free protein source for human consumption, the fibre-rich product was previously without a use.
However, the answer may lie in a newly discovered species of bacteria found within springs at Yellowstone National Park. By pre-treating the extracted fibre with sulfuric acid and breaking it down into sugars, the researchers were able to feed the sugars to the hot-spring bacteria and produce 2,3-butanediol, which can be used to create products, such as synthetic rubber and biofuels.
Now, the researchers plan to up-scale the process to keep up with the volume of spent grain generated by breweries. They also hope to find suitable enzymes and green chemicals to make this process even more sustainable and affordable.