Study: European Hops Are in Big Trouble

The science journal Nature published a study on the effect of climate change on hops grown in Czechia, Germany, and Slovenia, and the results are alarming. Researchers compared two periods, 1971-1994 and 1995-2018, to assess the current changes, and then projected the changes expected by 2050.

The changes in the second period show significant declines in yield and alpha acid content, and authors noted that hop ripening now begins three weeks earlier than it did in the first time window of the study. Looking forward, the ten authors write that by 2050, they expected “a predicted decline in hop yield and alpha content of 4–18% and 20–31% by 2050.” The effect is worse the further south the growing region. Below, more of the findings as well as a hopeful note about how these regions can boost their resiliency.

Let’s start with the findings.

Yield. Keeping in mind that latitude has a lot to do with this, the authors found: “The average annual hop yield decreased after 1995 by 19.4% in Celje [Slovenia], 19.1% in Spalt, 13.7% in Hallertau, and 9.5% in Tettnang, whereas the production remained stable in Zatec [Czechia] (0.05 t/ha).”
Alpha acid content. “The average alpha content decreased by 34.8% in Celje, 15.6% in Hallertau, 15% in Tettnang, 11.5% in Spalt, and 10.5% in Zatec.”
Outlier years. Few years in the later period saw larger-than-average yields and alpha acid levels, and they were offset by particularly bad years: “Declines in hop yields of more than 30% were recorded in 2000 and 2003. In 2006 and 2015, the decrease in alpha content was greater than 40%.”
Growing season. Thanks to warming temperatures, the growing season started on average two weeks earlier. “These phenological changes shifted the critical ripening period towards the warmer part of the season, which had a negative impact on the alpha content.”

The authors don’t offer a larger context for these findings, and it’s worth mentioning a couple things. First, the traditional/landrace varieties start out with comparatively low alpha acid contents to begin with: Saaz: ~3.5%, Hallertauer Mittelfrüh: ~3.5%, Tettnang: ~4.5%, Spalt: ~4.0%, Styrian Golding ~4.0%. Second, hops are very sensitive to terroir, or where they’re grown, so replanting fields in countries north of their origin points will change the flavors. However, there is some good news.

Unlike the dry summers that characterize the Pacific Northwest, Central European growers have historically relied on rain. Lack of water has a big effect on yield. “High yields and alpha contents were obtained in years when weather conditions were close to optimum conditions, whereas low values occurred in years with extreme weather conditions. Hop yields increased with precipitation but decreased after ~15% of normal precipitation.” Irrigation should be an easy way to boost production going forward.

The researchers didn’t look at other hop components, like oil and terpene levels, but it’s safe to assume climate change is affecting them along with alpha acid levels. They offer some thoughts on how growers might mitigate these changes:

“Hop farmers can and have responded to climate change by relocating hop gardens to higher elevations and valley locations with higher water tables, building irrigation systems, changing the orientation and spacing of crop rows, and even breeding more resistant varieties. Changing the orientation of crop rows and combining irrigation with water-saving soil management practices have proven to be effective adaptation measures in viticulture. It is important that the generative phase of hop plants occurs only in the appropriate photoperiod when sunshine duration is decreasing. This can be achieved by slowing plant growth via growth inhibitors or by building protective shading structures; which is, however, quite expensive. The higher probability of droughts can be partly mitigated by less frequent tillage and cultivation of hop fields, changes in fertilization and the use of row cover crops to support root growth.”

The full report includes details I didn’t mention and is worth a read for those interested in the topic.