Strategies for High-Value Utilization of Brewer’s Spent Grain: Applications in Bioactive Compounds, Bioenergy, and Environmental Sustainability

Brewer’s spent grain (BSG) is the by-product generated during the beer brewing process, accounting for nearly 85% of total by-products. Traditionally, BSG has been used as livestock feed due to its high availability and low cost; however, a considerable proportion is still discarded in landfills, raising both environmental and economic concerns. Importantly, BSG is rich in valuable nutritional and functional components such as proteins, fibers, and phenolic compounds, particularly ferulic acid, which provide it with significant potential for conversion into value-added products. In recent years, the valorization of BSG has attracted increasing attention as part of circular economy strategies in the food and bioprocessing industries. Therefore, a systematic analysis of BSG-based valorization strategies is required to identify efficient utilization pathways and to minimize waste. This review highlights recent advances in the high-value applications of BSG, with a particular focus on: (1) the extraction of bioactive compounds, (2) bioenergy production, and (3) development of biochar and biodegradable plastic materials. Furthermore, the challenges and future prospects of BSG valorization are discussed to provide insights for sustainable waste management and the development of bio-based industries.