Craft Brewers’ Spent Grains as a Secondary Resource: Chemical Profiling of Key Nutritional Components

Despite recent biotechnological advancements in the brewing industry, the effective valorization of spent grains from craft beer production remains challenging due to the nutritional variability of cereal-based raw materials. This study analyzes the proteins, free amino acids, fatty acids, and mineral composition of spent grains obtained from two beer types brewed with different proportions of maize grits and malted wheat, in order to assess the influence of adjunct composition. Protein content ranged between 25.81% and 28.43%, with higher values observed in the wheat-based spent grain. Total free amino acids were also higher in the wheat-based sample (190.03 mg/100 g) compared to the maize-based variant (178.66 mg/100 g). Both samples showed a similar fatty acid profile dominated by linoleic acid (51.39–51.58%), while phosphorus was the predominant mineral (up to 2700.03 mg/kg). These results suggest that adjunct type influences the nutritional characteristics of spent grains and provide a basis for their differentiated valorization in sustainable agri-food systems.