Upcycling of brewing byproducts into the brewing process

Abstract

This study explored the feasibility of incorporating brewers’ spent grain (BSG) and spent hops (SH)—the two main byproducts of the brewing industry—into the production of a novel beer, aligning with circular economy principles and sustainable process design. Preliminary trials demonstrated that SH retained significant bittering potential and that BSG, though partially depleted, still contained usable fermentable sugars. While acid and enzymatic pre-treatments were tested, they did not outperform conventional mashing. A Box-Behnken experimental design was used to optimize mashing conditions (rest times) for a mixture of BSG and malt. A semi-industrial brewing trial (70 L) was conducted under optimized conditions, and the resulting beer was evaluated through physicochemical analysis and sensory testing (n = 39). The optimized mashing regime (60 min at 62.5 °C followed by 22.5 min at 72.5 °C) produced wort with sufficient fermentable sugars. Beer produced at pilot scale using BSG, SH, and recycled yeast showed high bitterness (68 IBU), dark color (27 EBC), and elevated phenolic content (472 mg GAE/L), aligning with craft beer profiles. Consumer testing showed 82% acceptability with no significant difference compared to a commercial reference, though overall taste scores were slightly lower (average 6/10), with bitterness and herbal aroma noted as defining features. This work demonstrates that BSG and SH can be effectively upcycled to produce a beer with unique sensory qualities and market potential. The approach offers not only an innovative brewing concept but also a scalable and sustainable application for industry byproducts. Future work should explore recipe adjustments—particularly bitterness reduction through spent hops dosage optimization—to increase appeal among a broader consumer base. Given the successful scale-up and consumer acceptance, the process holds strong potential for commercial application, including patent submission and integration into small- to medium-scale brewery operations seeking sustainable and innovative product lines.