Brewery by-products: a resource to be valorised

Beer is the alcoholic beverage mostly consumed in the world, and it is gaining popularity through the birth of many local craft breweries. In the beer industry, the problem of the waste production is an emerging issue and three main types of by-products are generated, i.e. brewer’s spent grain, spent hops/hot trub, and residual brewer’s yeast. Globally, for every hectoliter of beer produced, 20 kg of spent grain are generated, for a total of 39 million tons per year. Brewery’s spent grain is rich in fiber and protein and is a potential source of valuable nutrients, including vitamins, minerals, amino acids and several phenolic compounds. Their composition is heterogeneous and varies considerably depending on the type and variety of cereals used, the type of hops and the brewing process. However, most of these by-products are used as animal feed or discarded. Recently several studies and research programs have focused attention on the possible reuse of spent grains in human food, composting, biogas, absorbents, building or packaging materials. Considering that the use of synthetic antioxidants in the food industry has been legally limited, the exploitation of agricultural residues as source of these compounds can be considered a sustainable and renewable alternative from a circular economy perspective. From this perspective, the possibility of use beer waste as a support for enzymatic immobilization was also evaluated, as its structural composition rich in natural fibers makes it a good candidate for this application. The goal of the present paper is to examine the recent developments on the valorization of brewery by- products in several industrial sectors, to present the experimental data of phenolic content and antioxidant capacity determined in the production residues of a local craft brewery, and to study the adsorption efficiency on spent grain through immobilization tests of the laccase enzyme.