Heat the burning problem for Oregon winemakers

A heat wave could cause problems for growers and growers in the Pacific Northwest of the United States.

By W. Blake Gray | Posted Tuesday June 29, 2021

How does Pinot Noir behave at temperatures of 116 degrees (47 Celsius)? We will find out.

The Willamette Valley, Oregon, had its hottest day in history on Monday, with temperatures reaching 116 degrees (47C) in Salem. It’s part of a thermal dome event that’s baking much of the Pacific Northwest: British Columbia hit 113 on Sunday, Portland hit 112, and Seattle hit its all-time high with a comparatively frigid 104.

Such temperatures do occasionally occur in the California wine country, particularly the San Joaquin Valley, where most American supermarket wines are sourced, and they are not particularly newsworthy. But pinot noir presents unique challenges for producers when the mercury reaches previously unimaginable heights.

“There are a few different aspects of Pinot Noir that make heat particularly difficult,” said Megan Kathleen Bartlett, professor of viticulture and plant biology at UC Davis. “Part of that is the style. You are looking for less tannins, you want a higher pH in the berries, and you want less sugar so you have less alcohol. All of these things are affected by heat. Heat breaks down. really. acidity. And that increases the amount of sugar that the plant sends directly to the fruit. It also increases the evaporation of the fruit. It is a thin-skinned grape, so it is very prone to evaporation, to the fruit. wilting and sunburn. “

Fortunately, this may be the time of year when the vines resist heat the best. Jim Bernau, founder and CEO of Willamette Valley Vineyards, told Wine-Searcher that Willamette Valley had twice its normal rainfall earlier this month, so the soil has a bit of moisture, and also the vines don’t. have not yet undergone veraison, so the berries are still tiny, green and hard.

“If you had to pick a time that would be least harmful to the vines, it would be now,” Bernau told Wine-Searcher. “We have already gone through flowering. We have already gone through fruit set. We had a June so wet that we have overgrown in the canopy. Our clusters are covered. Because the clusters are so young, they are just right. tiny little berries sheltered by the leaves. “

Grape leaves have stomas, small openings, which normally let in CO2 and which exhale oxygen and water vapor. In extreme heat, the stomata close to conserve water and protect the plant. But if they stay closed, it can lead to leaf death, Bartlett said, and the leaves are crucial for both ripening grapes and protecting them from the sun.

Just like with humans, sunburn is a threat to grapes. Bartlett said it’s more evident in white grapes, which can brown in patches, but it threatens red grapes as well. Bartlett said UC Davis had researched creating solar shelters for vines using fabric, but a larger canopy of leaves is the best way to go.

Gregory Jones is a research climatologist at Linfield University in McMinnville in the Willamette Valley. Jones is the wine industry‘s leading expert on climate and global warming; I joined him in his car on Monday where his air conditioning protected him from the 110 degree heat.

“The biggest challenge with a heat wave like this is that the last two days and tomorrow will likely be 25 to 30 degrees above average,” Jones said. “What makes the Pacific Northwest so conducive to cool climate grapes is that we usually don’t see such things. The northern Willamette Valley is hardly irrigated. Without irrigation, you won’t. not much can be done. It was a time when most of the canopies are at their full growth. There is probably enough growth to provide shade and keep the berries a little cooler. But there is concern that this does not cause performance problems. “

Water concerns

Once mature, the vines are hardy and resistant; I said this afternoon to a non-enophile friend, “Think of them as very pampered and successful weeds.”

“Vinifera has evolved on sunny volcanic slopes in much more hostile environments than the Willamette Valley,” said Jason Lett, owner of The Eyrie Vineyards in McMinnville. “The vines will do just fine. When I was outside today, the vines looked great – no cupped leaves, lots of tendrils, lots of vigor. Plus, the heat kills powdery mildew, which , I love that.”

Older vines will have roots that descend to cooler, wetter soil; Bernau said: “These old Pinot Noir vines, their vines are beautiful and fresh.” But younger vines that have been recently planted and are not irrigated risk dying. And while the long-term health of old vines might not be impaired, this year’s harvest may be affected.

To draw a parallel, consider the 2003 vintage of Burgundy, when a heat wave caused temperatures to rise across Europe. Burgundy winemakers produced a lot of wine in 2003 and it is certainly drinkable, but the wines are known to have higher alcohol content and less acidity than usual. In parts of Europe this was a plus, but as Bartlett points out, it’s not what a lot of people look for in good Pinot Noir.

Oregon Wine Board spokesperson Sally Murdoch said, “We’re more worried about the people right now than the grapes.” In fact, Portland and Seattle have some of the lowest air-conditioned housing rates in the United States. Less than 50% of Seattle homes are air-conditioned, and I personally have a friend whose family moved from Seattle to Phoenix (!) To weather the heatwave in an air-conditioned hotel with a pool. Cities in the region are opening cooling centers that people can visit in the afternoon.

“It’s rush hour for vineyard work, with the vines requiring training, shoot management and leaf pulling,” Lett told Wine-Searcher. “These hot days mean we can’t work full days, which slows us down just as the vines are thriving. This will make it even more difficult to follow up. Lett said the cascade of postponed tasks will result in an extra-grueling harvest season when it finally happens.

Jones said the impact of climate change is not apparent in the fact that there is a heat wave, as there have always been heat waves, but in its magnitude.

“These heated domes are getting as big as this one, which is the kind of thing we would expect in a warming climate,” Jones said.

Bernau has said he hopes this thermal dome will be the last rider of 2020-21.

“There is always something. Think of the Four Horsemen of the Apocalypse,” Bernau said. “The first was the pandemic. The second was that it rained so much last year that it reduced our yields more than ever in the Willamette Valley: 38% on average. The third was smoke. [last year]. And this is the fourth. We hope this will be the last rider. “

About Michael Brafford

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