Late-season irrigation lapses impact the physiology, yield, and metabolite production of Yakima Valley hops

Authors: Gonzalez Tapia, Francisco

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2025
Publication Date: 5/23/2025
Citation: Gonzalez Tapia, F. 2025. Late-season irrigation lapses impact the physiology, yield, and metabolite production of Yakima Valley hops. Journal of the American Society for Horticultural Science. 150(3):136-146. https://doi.org/10.21273/JASHS05461-24.
DOI: https://doi.org/10.21273/JASHS05461-24

Interpretive Summary: Hops, the cone-shaped flowers of the hop plant, are essential for giving beer its characteristic aroma, flavor, and bitterness. In Washington State’s Yakima Valley, which produces the majority of hops in the United States, consistent water for irrigation is vital for growing high-quality hops. However, climate change is reducing water availability, posing significant challenges for hop production. We examined how cutting off water late in the growing season impacts hop plants. By withholding irrigation 15 days and 30 days before harvest, we evaluated changes in plant health, yield, and the chemical compounds that affect brewing quality. Our findings show that even short periods without water late in the season can stress the plants, reducing their ability to convert sunlight into energy and significantly lowering yields. The earlier water is cut off (30 days before harvest), the greater the reduction in yield. Despite this, the bitterness compounds crucial for brewing remained stable, meaning that drought-stressed hops still meet brewing quality standards for bitterness. However, the compounds responsible for hops’ aroma and flavor, known as essential oils, were more sensitive to water shortages. While some aroma compounds decreased under drought conditions, others increased when water shortages occurred earlier. These changes could alter the aroma and flavor of beer brewed with these hops. To minimize the impact of late-season water shortages, it is essential to keep the soil well-watered before any potential irrigation disruptions. These results offer important guidance for farmers and brewers, helping them adapt to climate challenges while continuing to produce high-quality hops and beer.

Technical Abstract: This study investigates the effects of irrigation water loss late in the season on hop physiology, cone yield, and essential oil composition in the Yakima Valley, a critical hop-growing region vulnerable to water shortages. The research examines the impacts of withholding irrigation 15 days and 30 days before harvest, comparing these treatments to full irrigation during a two-year period. Withholding irrigation caused significant physiological changes, including reduced stomatal conductance, transpiration, and photosynthetic efficiency, highlighting the sensitivity of hop plants to late-season water shortages. Withholding irrigation water 15 days before harvest reduced yield moderately (9.5%), while at 30 days the lapse caused more severe declines (28.8%), emphasizing the heightened vulnerability of hops to extended drought earlier in the season. Bittering compounds, such as a-acids and ß-acids, exhibited remarkable stability across irrigation treatments, suggesting drought-stressed hops can maintain brewing quality. However, minor reductions in cohumulone content were observed, though they were not biologically significant. In contrast, essential oil composition showed notable variability. Monoterpenes, including geraniol, linalool, and ocimene, decreased under water shortage conditions, likely due to disrupted photosynthesis and altered carbon allocation. Conversely, some monoterpenes, such as citral and geraniol, increased during earlier drought stress. Sesquiterpenes, including humulene and caryophyllene, generally increased under water shortage conditions, particularly with earlier water stress, suggesting an upregulation of sesquiterpene biosynthesis. These findings underscore the critical importance of water availability during late stage hop development. While bittering compounds were stable, significant yield reductions and shifts in essential oil profiles could impact both hop growers and brewers. Our findings suggest that the impact of late-season water shortages may be mitigated on hop production by maintaining soil water content at or near full capacity in anticipation of irrigation disruptions. This research provides valuable insights to inform adaptive irrigation practices and support the sustainability of hop production under changing climatic conditions.