Smoke Exposure in Hops: Comparisons of Field and Kiln Smoke Sources and the Impact on Hop Quality

Wildfires continue to plague the Pacific Northwest United States annually from July to October, presenting challenges to hop growers and brewers alike.  Producing the finest hops in North America now requires understanding how wildfire smoke exposure impacts their characteristics. To that end, the Shellhammer lab is investigating how environmental smoke in-field or during kilning/drying ultimately impacts hop and beer quality. This presentation focuses on results from controlled smoke exposure experiments to hops during late maturation in Oregon hopyards and separately during kilning/drying over two harvest seasons. For the in-field trials, selected Citra® hops were exposed prior to harvest using large chambers to contain smoke from burned mixed fir species pellets. For the kilning trials, Cascade hops were exposed to smoke during drying from the same mixed fir species pellets, as well as pellets made from grass seed cuttings. The potential for mitigation by filtering the kiln intake air was also explored. Results indicated that kilning with smoky air could produce smoke-affected Cascade hops, with smoke-related chemical markers (volatile phenols “VPs”) and sensory attributes increasing as the concentration of particulate matter in the kiln intake air increased. Filtering kiln intake air showed promise as a mitigation method, but more research is needed. Also, VPs were transferred from kiln-smoke-exposed Cascade hops to beer dry-hopped with those hops, and accompanied by increases in undesirable smoke-related sensory characteristics. The results from the in-field trials were mixed, indicating that in-field exposure may not be a significant vector for smoke-taint in Citra® hops. Though smoke-related chemical makers were identified in field-smoke-exposed Citra® hops, sensory results were inconclusive with some replicates showing differences from controls and others unable to be distinguished by a trained sensory panel. These results provide the first evidence regarding the importance of smoke sources for smoke-affected hops and may be used by growers and brewers to better understand and mitigate the deleterious effects of wildfires during hop harvest.