Milling as a pre-treatment in the food uses and fractionation of brewer's spent grain

The brewing industry generates relatively large amounts of by-products and wastes, such as spent grain, spent hops and yeast. Brewer's spent grain (BSG) is the insoluble cereal residue that is separated from the mash before fermentation, and it is the most abundant by-product. Even though BSG is a low cost material and available in large quantities around the year, it has been used mostly as animal feed so far. However, if properly separated from BSG, the carbohydrate and protein fractions could be turned into more valuable products, and new applications are constantly being developed. To enable the use of BSG fractions in more valuable applications than animal feed and combustion, cost-efficient technologies to separate the different fractions must be developed. Applying and combining mechanical and chemical treatments and enzymatic hydrolysis are the main technologies, which have been attempted in BSG fractionating. In this study, various milling technologies were used as pre-treatments for BSG fractionation. The milled fractions were characterised and used as food ingredients as such, or subjected to enzymatic hydrolysis. The particle size of BSG was significantly reduced by ultrafine-milling. Impact milling using a 0.3 mm sieve and ultrafine milling gave average particle sizes of 200 m and 33 m, respectively. The small particle size of ultrafine BSG enabled the suspension of BSG into liquids. The sensory properties of milk- and juice-based beverages containing ultrafine BSG were evaluated. The mouthfeel of products containing ultrafine BSG was good. The overall sensory quality was dependent on the serving temperature of the drink. Milling had a positive effect on the subsequent hydrolysis. However, in all cases a recalcitrant insoluble residue consisting of lignin and unhydrolyzed carbohydrates remained. Milling as a pretreatment was shown to enhance the hydrolysis of carbohydrates.