Review of Brewer’s Spent Grain Valorization: Technologies, Safety, Circularity, Citizen Implication, and Future Opportunities Using a Plan–Do–Check–Act Framework

Brewer’s spent grain (BSG) has attracted rapidly growing interest, and a considerable body of fundamental and applied information is available in the literature, although each source addresses only one or a few aspects of the topic. Based on the recent literature, this review provides a full picture of BSG valorization, from basic to applied sectors. This includes valorization technologies at the design level, such as those for packaging and textiles, as well as those that have achieved market success, such as food ingredients. The review addresses moisture and linked microbial deterioration, contaminants, industrial milestones, sensory limitations, and regulatory barriers concerning BSG valorization. More interestingly, it presents the Plan–Do–Check–Act methodology and shows how to use it for BSG valorization, regardless of its scope and level of technology readiness. The proposal is centered on the citizen as a stakeholder of the entire food chain leading to this or any food waste. The review also aims to fill gaps in the field and affords recommendations for future research directions towards a more sustainable economy.