How Climate Change Will Affect Your IPA

I just received my annual issue of Hopfen-Rundschau, which arrives a month or two after I’ve forgotten it exists in a beaten-up brown wrapper—as if containing something more illicit than the latest news about German hop research. As usual, this issue contains many nuggets of fascinating info (as well as tons of boring hop-industry executive changes and awards), and today I’m going to tell you about research looking the effect of climate on hops.

It turns out that Germany was presented with a perfect natural experiment. In 2015, the country suffered through 34 days of excessive heat. The average number of days of excessive heat from 1980-2008 was just five (it went up to ten over the next five years, and fourteen over the past five). However, the following year was close to historical averages, with just 7 days of excessive heat. Researchers have long known that very hot, dry summers result in lower crop yields and lower concentrations of alpha acids. But what happens to other elements, like oil, terpene, and polyphenol content? More importantly, what impact do these differences have on the flavor and aroma of the resultant beer?

The researchers chose two modern hops selected for their aromatic compounds (Callista and Ariana) and brewed a hoppy lager in the American style with them (including lots of late-, whirlpool, and dry-hop additions). In a stroke of genius, they normalized the amount of those late additions by oil volume, not hop weight, so they would have an apples-to-apples comparison.

The results were fascinating. Not only did the two hops behave differently in the hot and dry years, but the heat increased some elements and decreased others:

  • Alpha acids were, as predicted, higher in the cooler year. Beta acids, however, were only marginally higher in the Ariana (5.2 vs 5.5 %w/w), but were substantially higher in Callista (5.9 vs 7.8).

  • Cohumulone rations, xantholhumol, and total polyphenols were unaffected.

  • Both varieties had higher oil content in the cooler year.

  • Linalool content was a touch higher in the cooler year, but geraniol and geraniol acetate levels were much higher in Ariana during the cooler year—but unchanged in Callista.

  • Added together, all monoterpenes and “total calibrated substances” (everything they measured) were far higher in the cooler year, but sesquiterpenes levels were little changed.

  • Esters in the finished beer were more than three times higher in the cool year for the Ariana-hopped beer, but were about 25% lower in the Calista-hopped beer.

In 2015 [the hot year], the concentration of compounds readily soluble in beer was around 25% lower in Callista and 50% lower in Ariana. Callista appears to successfully retain its astonishingly high aroma potential, even in years when climate conditions are more challenging.

The researchers also did taste trials on the different beers (and included 2017’s crop—another cool year with just 11 excessively hot days). They rated the beers on aroma intensity, aroma quality, aroma descriptors, and bitterness intensity and quality. In the case of both hops, the hot year was rated the lowest, but ratings were far lower for the Ariana-hopped beer than the Callista. (Bitterness was not affected too much—though the disparity was higher in the Ariana beers.)

Hot weather will increasingly damage yields, and there’s no getting around that. Among four bittering hop varieties researchers studied, crop yields were down 25% in 2015. They were down 47% among the nine varieties of aroma hops. There’s a hopeful note in this research, however. Different strains will react better or worse to the heat. While none of the hops are likely to benefit from hot, dry summers, some will suffer the conditions only mildly. And that’s good news for you hopheads out there.

Jeff Alworth2 Comments