Lifting craft breweries sustainability through spent grain valorisation and renewable energy integration: A critical review in the circular economy framework

Due to the constantly growing customers’ demand for local products, a significant rise in craft breweries' number, as well as in craft beer production, has been observed in the last years. The sustainability of craft breweries is a hot scientific topic, which involves water and waste management, energy efficiency, and renewable energy implementation. Life cycle assessment (LCA) and life cycle costing (LCC) are useful tools to compare alternative waste management pathways in a standardised manner, highlighting the hotspots with the highest environmental/economic impact. Brewery-spent grain (BSG) represents the main organic by-product of beer production; traditionally, it has been used as animal feed. However, not always there are enough farms to utilise all the produced BSG locally, especially in developed countries and industrialised areas, so alternative solutions should be exploited. This review gives a thorough overview of the different technological pathways for BSG valorisation considering the state-of-the-art of research on the topic, including both traditional (animal feed, composting, anaerobic digestion) and innovative (thermochemical processes, pellets production, food production, chemicals' extraction) solutions. The applicability of each technology to craft breweries is specifically discussed. To enhance craft breweries’ sustainability and decarbonise industrial processes, renewable energy generation is considered as well either through photovoltaic (PV) or solar thermal: while solar thermal implementation appears cumbersome due to the batch nature of the processes, PV installation is a mature, simple and straightforward solution. Geothermal energy integration is mentioned as well. Finally, a lack of studies on LCA/LCC application to compare the presented alternative BSG management pathways is highlighted, requiring intensive future research.