Hop Science - June 2026

Keep away from the fire!

As wildfires become more frequent and severe in major hop-growing regions, there is increasing concern about how smoke exposure may affect hop quality. This study investigated the effects of kilning Cascade hops under different air quality conditions using a pilot-scale system in which smoke was generated by burning mixed fir pellets. The results showed a moderate positive correlation (R2 = 0.6815) between air quality, measured by the Air Quality Index (AQI), and the total concentration of volatile phenols (VPs) in the dried hops. Guaiacol and 4-methylguaiacol accounted for most of the total VPs (55–79%), most likely as a result of lignin pyrolysis from the fir wood. Conventional hop quality parameters, such as alpha acids, HSI, total oil content, and oil composition, were not affected, although some volatile terpenoids, including geraniol and citral, increased slightly as AQI rose. Sensory analysis, using check-all-that-apply and line-scaling methods, showed that higher VP levels were associated with lower citrus character and reduced overall hop aroma intensity, while smoky, meaty, and artificial BBQ notes were reported more frequently. These results suggest that smoke-exposed hops can retain their core analytical quality parameters while still showing a clear sensory decline due to the uptake of phenolic compounds. The study therefore highlights the importance of combining chemical and sensory analysis to evaluate smoke taint in hops and to guide postharvest handling in regions at risk of wildfires. 

Jobe CA, Shellhammer TH. Kilning with smoke-affected air impacts the chemical and aromatic qualities of Cascade hops. Food Res Int. 2026 May 31;232:118800. doi: 10.1016/j.foodres.2026.118800. Epub 2026 Feb 26. PMID: 41895926. 

Hops for the chicken?

Antimicrobial resistance has increased the need for alternative ways to control pathogens and support poultry growth, including the use of plant-derived hop isolates. This study investigated how five major hop compounds—humulone, lupulone, isohumulone, xanthohumol, and isoxanthohumol—interact in their biological activity against Bacillus subtilis, Micrococcus luteus, and the chicken cell line UMNSAH/DF-1 using a two-dimensional checkerboard assay. Interactions were classified as additive, synergistic, or antagonistic using fractional inhibitory concentrations, and selectivity indices were used to compare antibacterial activity with cytotoxicity. In Bacillus subtilis, most combinations were additive. In contrast, Micrococcus luteus showed more variable responses, including synergistic effects such as humulone plus lupulone and antagonistic effects such as isohumulone plus isoxanthohumol, showing that the metabolic resilience of the target organism influences the outcome. Cytotoxicity in UMNSAH/DF-1 cells was also mainly additive, with synergistic effects observed only for the isomerized compounds. Selectivity analysis identified the humulone-lupulone combination as the most favorable, indicating moderate to good antibacterial selectivity. Overall, these findings provide useful guidance for selecting combinations of hop compounds for the development of phytogenic feed additives and show that both compound composition and the physiology of the target organism play a critical role in efficacy and safety. 

Kober L, von Karger L, Castiglione K. Mixture dependent correlation patterns in antibacterial and cytotoxic activities of five hop isolates. Sci Rep. 2026 May 30;16(1):16805. doi: 10.1038/s41598-026-55473-1. PMID: 42225839; PMCID: PMC13226645. 

Don’t throw away the leaves!

Hop leaves, a so far unused by-product of hop cone harvesting, are a rich source of quercetin and kaempferol 3-O-glycosides. This study characterised ethanolic hop leaf extracts and phenolic standards with regard to their antioxidant activity using FRAP (ferric reducing antioxidant power), DPPH (2,2-diphenyl-1-picrylhydrazyl), and ORAC (oxygen radical absorbance capacity) assays. Purified extracts were treated with snailase, a commercial enzyme mixture, to hydrolyse the glycosides. The resulting digests were then analysed for antioxidant activity and phenolic composition using LC-ESI-qTOF-MS/MS. The flavonol glycosides present in hop leaves showed significantly lower antioxidant activity than their corresponding aglycones. Treatment of the leaf extracts with snailase achieved hydrolysis rates of more than 99% and led to a significant increase in antioxidant activity, with the fold-change depending on the glycoside composition and the mechanism of the antioxidant assay used. The treatment was especially effective for the hop variety Cascade, which showed a 4.5-fold increase in FRAP, due to its high content of kaempferol 3-O-rutinoside (400 mg/g). For the first time, this study demonstrates the production of antioxidant-rich hop leaf extracts using snailase and supports these findings with a comprehensive underlying analysis of both the extracts themselves and the antioxidant activities of pure standards representing the predominant compounds. 

So should we give hop leaves more appreciation? 

Calvert D, Dew T, Gadon A, Gros J, Cook D. Hop leaf phenolics as a source of natural antioxidants. Food Chem. 2026 Jul 1;516:149289. doi: 10.1016/j.foodchem.2026.149289. Epub 2026 Apr 17. PMID: 42034088.