Hop ( Humulus lupulus L.) Residual Biomass: Attributes, Past Experiences and Opportunities for Future Utilization

Hop (Humulus lupulus L.), a perennial climber plant, has a significant agricultural and industrial presence, primarily valued for its cones in the beer brewing industry. However, the residual biomass, comprising leaves and bines, is often underutilized. Research has highlighted the vast utilization potential of this biomass, which can be effectively utilized as a source of bio-fertilizers through bio-composting, and traditionally for medicinal and fodder purposes, too. Additionally, hop residual biomass has been identified as a potential bast-fiber crop, comprising phloem fibers and woody core. The structural carbohydrates in the hop stem, including cellulose, can have great potential for pulping and production of nanocellulose. Furthermore, the phloem fibers can be used as a filler in natural fiber‑reinforced composites, influencing their mechanical properties. The annual discharge of hop residual biomass in the European Union alone is estimated to be around 100,000–120,000 tons, underscoring the need for sustainable utilization strategies. This review highlights the importance of utilizing hop biomass residues as a raw material for a range of applications. Additionally, by developing efficient processing technologies, the full potential of hop residual biomass can be unlocked, reducing waste and promoting a more circular and sustainable economy.