Sightglass: What Happens to Beer When the Nights Warm?
The Sightglass project is a collaboration between Beervana and Reuben's Brews. Together, we select a topic of mutual interest and I write about it. In some cases, Adam Robbings and Matt Lutton will interview one of the central players for their podcast, also called Sightglass. Articles in this series include "How a Hop Earns its Name," "The Future of Yeast,", "How Women Enrich Beer," and How Craft Malting is Transforming Beer.
For over a century, the Pacific Northwest has been a great place to grow hops. The sun burns long in the northern sky, the summers are largely free from rain until late September, and the nights are cool. But with a warming climate, the calculus has changed. Those conditions, along with millions of acres of tall fir and pine trees, have made the region a summer tinderbox. When forest fires rage for months, smoke regularly settles on hops, tainting them with brimstone.
That dry, baking heat has also begun to affect the North American barley crop. This year, it roasted the fields, leading to startling declines in yield. Water, the lifeblood of beer, is scarcer in the west, and groundwater supplies are increasingly vulnerable as well. Of course, this isn’t confined to the US. Across Europe, floods, extreme heat, and drought have damaged recent crops.
Yet beer isn’t just facing an existential crisis. Long before the ingredients for beer are endangered, they’ll change and adapt to these conditions. Few plants are more sensitive to subtle changes than hops, so dramatic effects like heat domes and early summers will certainly change the way they taste. I recently spoke to a researcher looking into these effects, and she suggests the changes may be unexpected—but not necessarily all negative. Climate change is incredibly complex, and one little-studied factor is the focus of Dr. Colleen Doherty’s research: what happens to plants as the nights warm?
Changing Climates
Few in the Pacific Northwest doubt the dangers of climate change—we have seen too much of it. Early this summer, a “heat dome” settled over the region, producing temperatures ten degrees higher than any ever recorded here. The singed little hops mostly rebounded from this shock (pdf), and the crop wasn’t too badly damaged—but just a year ago dense smoke damaged many acres. Each year we know to brace for the worst.
The 2021 North American barley crop is another piece of dire evidence. It was a disaster—and may affect the industry for years, even if next year’s harvest is normal. How bad was it?
The American Malting Barley Association (AMBA) reported last week that overall barley production in the US is down 31% to 2.6 million tons from the 2020 total of 3.7 million tons. The average yield per acre was down nearly 22% over last year’s. The poor harvest results were due to excessively hot and dry weather patterns in many regions throughout the growing season.
Beyond the shortage, the crop that did come in was poor.
“Not only is North American barley production way down, but there are serious quality issues as well…. The average protein level in this year’s malting barley crop is north of 14 percent compared to the usual 11 to 12 percent range.” In addition, “Rain in the third week of August [in Canada] caused chitting, or premature sprouting of barley in the swath. That product will be fine to process in the short term, but it will lose germination over the long haul.”
These trends are chronic and trans-continental. One solution may be moving production to cooler climates, but farmers already use the best cool-weather farmland for other crops. Scientists have also been addressing the issue by breeding new varieties more resistant to rising temperatures and drought. Yet in its complexity, climate change has been throwing curveballs at growers that have been little-appreciated until recent years. One of the most interesting is Colleen Doherty’s subject of inquiry, and it’s a good example of just how the “change” in climate change may affect our beer.
Warmer Nights
Colleen Doherty is a professor at North Carolina State, a biochemist, and founder of the Doherty Lab. She investigates the relationship between time and stress in plants, and particularly, “how changes in temporal patterns (earlier springs, warmer nights) affect the productivity of crop species.” Temperatures fluctuate during the day, and we tend to focus on the daytime highs, which are more obvious to diurnal beings like us. They’re spiking up fairly dramatically, heat domes aside, and we have taken note.
Colleen Doherty
Yet it may be the nighttime lows that affect plants most. In fact, hotter days can be beneficial for crops, driving yields up. Warming nights, not so much. The reason has less to do with the temperature itself than the plant’s expectations. Plants accumulate sugar through photosynthesis during the day and they burn it at night. Normally this process is balanced; the plant knows exactly how much of its stored energy it will burn over the course of the night. But here’s the rub: “With warmer nights,” Colleen explained, “that pathway is being disrupted. Every biochemical reaction is affected by temperature. With this is a very small temperature change—we’re talking about one degree or two degrees—their clock gets screwed up.”
This was completely new to me and I had to interrupt and ask Colleen to back up. Why does temperature affect energy use? She reframed the process by way of metaphor:
“Carbon is the money for plants; it’s their currency. They get the carbon from the carbon dioxide, during the day they store it, and then they burn it at night. Plants have to decide, ‘Am I going to put more energy into making a new leaf, or am I going to put more energy into a tuber, am I going to put that into the root, or am I going to use it to make defense compounds to protect me?’ Every decision is about how to spend that carbon. That’s their budget. Climate change is essentially introducing a deficit into that budget, and so now they have to reallocate how they’re spending their carbon.”
But why would a warmer night affect this allocation process, I asked? “Essentially their respiration increases,” she said. “So they’re not burning more, but the feedback to tell them how much they’re burning is messed up. This is not heat stress. Their [nighttime] trough is just a little bit higher. It’s amazing that that’s disruptive when they have this massive swing between the day and night temperature.”
Chemical Changes
Nighttime temperature rises also effect other organisms. Microbes, fungi and mildew, and insects are all more active and vigorous when the nights get warmer. Plants have the capacity to combat these threats by producing particular defense compounds. Known as “secondary metabolites,” these compounds don’t affect growth or a plant’s primary processes like the carbon metabolism Colleen described. Instead, they help mediate interaction with their environment—and protect them from organisms. Common secondary metabolites? Things like terpenes and phenols—the very chemicals that flavor and scent our IPAs. It makes sense. Humans started using hops because of their antimicrobial compounds—humulene and myrcene derivatives are examples—so it’s not surprising the hops use them to protect themselves as well.
“We think a lot of these metabolites are defense compounds in hops, the ones we really love,” she told me. “We think that about coffee. These things that are involved in taste that attract mammalian taste receptors are also protecting the plant.” In a changed environment in which plants are encountering more predators, they may well start to produce more of these flavor compounds. It could create a situation in which plants have to produce more of the compounds brewers love to compete.
I asked whether this was an element of terroir, and Colleen immediately agreed. It goes beyond sun and soil to microbiology and—perhaps—nighttime temperatures. It made me wonder if the blend of predators in the Pacific Northwest was particularly robust, given the way American hops express such vivid character. Unfortunately for me, she is a researcher, not a pundit, and didn’t hazard a guess to a question outside the scope of her research. The pathogens could cause plants to make more defense compounds, but Colleen hasn’t done real-world studies. However, she did note that “we can safely infer that things will be different because in every crop we look at the carbon itself is different, and that’s going to affect the specialized metabolites.” We’ll have to wait and see.
More Alarming Effects
Warming nights won’t just affect secondary metabolites. They will affect yield, particularly in barley. Early research twenty years ago suggested a relationship between warmer nights and lower crop yields, but it was an economics paper in 2008 that really rocked Colleen. The paper looked at rice crop yields, trying to include every variable researchers could find. “They found [a strong] correlation with the rice yield [and] warmer nights. The daily minimum temperature was predictive of lower yields. The daily maximum temperature was predictive of higher yields.” Subsequent studies have confirmed the findings, and the effects aren’t small. Some studies have found that when nighttime temperatures rise as little as one degree on average, yields can decrease by 10%.
The warmer nights are related to a change in the planetary boundary layer that traps more heat overnight. Given how complex our climate system is, trying to account for all the intricate interrelations has confounded climate models. She mentioned that scientists have only recently begun to appreciate the role warmer nights play in all of this. That makes it all the more difficult to guess what the climate—and crops like hops and barley—will face twenty or thirty or forty years down the road.
“Nature is very intricately intertwined and there are all these organisms and they’re all set to the rotation of the earth, the environment of the earth as it’s been the last 200 million years.” And now nature is changing to respond to new climate conditions.
One thing is almost certain: as that future arrives, the warming climate is going to play a central role in beer-making, for worse—but possibly, in a few cases, better as well.