Upcycling of brewers’ spent grain flour: physicochemical characterization and potential applications

The study considers the reuse of brewing industry residue, known as brewers’ spent grain (BSG), by transforming it into flour and analyzing its physicochemical properties and possible applications. The raw material was provided by a Portuguese brewery and dried at 40 °C for 24 hours, followed by milling. Subsequently, the flour was analysed for physicochemical parameters, and characterization was performed using Fourier transform infrared spectroscopy (FTIR). The physicochemical results showed that the brewers’ spent grain flour has a low moisture content (6.93%), a relatively moderate water activity (0.48), and a slightly acidic pH (5.02). It also showed a high protein content (32.31%) and a considerable ash content (3.73%), indicating the presence of minerals. Despite the low moisture content, the higher water activity suggests greater availability of free water, which may promote chemical reactions or microbial growth if storage conditions are not properly controlled. This behavior is explained by its composition, rich in proteins and insoluble fibers, which retain less total water but make part of it more available. Mineral analysis showed that the brewery residue mainly contains phosphorus (9.38 mg/g), magnesium (1.55 mg/g), calcium (0.46 mg/g), and zinc (0.20 mg/g). However, overall, it has a lower mineral content than other agro-industrial residues, such as those derived from viticulture. FTIR analysis confirmed the presence of various organic compounds, including hydroxyl groups, aliphatic chains, esters and aromatic structures. Components typical of plant biomass, such as cellulose, hemicellulose, and lignin, were also identified, as evidenced by characteristic bands in the spectrum. Taken together, the results show that brewers’ grains have high nutritional value and functional potential and can be used as a sustainable ingredient in the food industry, helping to valorise agro-industrial by-products and cutting waste.