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On Wine

Dan Berger On Wine: We're having a heat wave

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The heat dome that hit the Pacific Northwest July 4-7 was uncomfortable for most, negatively affected the health of some, but didn’t really cause much harm to the Oregon and Washington wine industries, which avoided a nuclear calamity because of when it occurred.

That’s the view of one of the nation’s most respected climatologists and viticulture experts, who termed the Oregon/Washington heat spike a “once-in-a-lifetime” event that’s unlikely to happen again soon.

But as a harbinger of the impact of global climate change, it gave the wine industry at large a definitive warning shot and a chance to assess what winegrowers face down the road, not only for future heat domes, but for climate change, said Greg V. Jones.

Jones, a former professor of Linfield University’s Environmental Studies department in McMinnville, Ore., noted that the heat episode, in which temperatures soared well above 110 degrees, “could have been much worse.

“But it happened at a time in the vine’s growth cycle that the effect was minimal — about as good as it could have been,” said Jones, who recently resigned from Linfield.

It’s well known that grapevines are self-protective and hard to destroy under all but the most extreme stress.

Vineyards in Oregon and Washington were “well past flowering and berry set,” said Jones. “If it (the heat dome) had occurred two to three weeks earlier, the damage to the flowers would have been devastating. And if it had happened two to three weeks later, the berries would have been damaged.

“Not only would maturation stop, as the vines shut down to protect themselves, but there would have been tremendous shriveling,” and strange flavors would have developed.

A few Oregon and Washington vineyardists may have had some trouble if they didn’t prepare at all for the heat dome. He said he heard of a few people “who were pulling leaves” in anticipation of a normal year, “which could have caused more damage through desiccation and too much direct sunlight on grapes.

“If you had irrigation and used it for two, three, or four days before the heat, that would have helped the vines – and older vines did better (than young vines) because their roots go down further to search for water.”

Jones also pointed out that viticulturalists know a lot about how grapevines react to very cold conditions, “but we know very little about the upper limits of temperature,” like about 95° -- “just before vines begin to shut down.”

A key point, he emphasized, is that the 95 degree reference point he mentioned seems to be far more important with some varieties than it is with others. As a result, he referenced work being done in Australia to identify various climate sensitivities of grape varieties that are uncommon – and in some cases, grapes that are completely obscure.

He said much work still needs to be done in this area of heat tolerances, in particular because of global climate change and what its effect will be on vineyards down the road. He added that research must be done on what growers can do to deal with long-term and short-term heat episodes short of drastic vine-removal and replacement techniques.

He noted that the University of Adelaide’s Roseworthy Agricultural College, working with the Australian Wine Research Institute (AWRI), has invested heavily to identify grapevine and berry temperature issues related to climate change, partly as a result of the Australian bushfires and the extreme drought conditions that country’s wine industry has faced in recent years.

“As a climatologist, I’m amazed that (the Oregon/Washington heat dome) was as far north as it was, and the size of it,” said Jones, who has a doctorate in Environmental Sciences.

He said the damage that heat can do to vines seems to be varietally linked – that is, some grape varieties do better under excessive heat than do others. And even rootstocks may be involved.

“There is some evidence that if you have a good rootstock-scion match, the vines have a better chance to manage heat and drought,” he said, referring to work done in Australia by Kym Anderson, professor emeritus of economics at the University of Adelaide.

Additionally, vine adaptation plays a key role in how plants react under extreme conditions, Jones said, which benefits more mature vines.

“Adaptation is really important because over time any plant will adapt to its environment. Some varieties are more cold-adapted,” and in those cases can produce aroma and taste characteristics that may be directly related to vineyard temperatures.”

As a result, older vines in very warm to hot regions, such as in California’s southern San Joaquin Valley, have adapted to regular 100° days. Jones added, “Also, soils in the (Central) Valley are deep, so if the vines have a better chance at survival, it’s because roots can go down further seeking moisture.

“Thin soils plus drought conditions is a really questionable combination.”

A Sonoma County winemaker who has participated in more than 40 harvests said he has experienced several hot spells over the years, and that occasionally drastic measures were needed to make a sound wine.

“In 1979 it hit 116 degrees in Calistoga about harvest time, and maturation nearly ceased,” he said. “We picked just after we hit 20 degrees brix,” which would have made a wine with about 11% alcohol and “would have been really thin.”

“So we chaptalized,” he said, admitting to a practice of adding cane sugar to the fermentation vat, which was and still is illegal in California. He said the resulting was good enough to sell.

“It certainly beat the alternative — to dump the vintage,” he said.

A point of reference: Global climate change has so altered some wine-growing districts in Europe that French government authorities recently permitted the planting, in some regions, of grapes that previously were outlawed.

For example, Touriga Nacional, a heat-tolerant grape of Portugal, now is allowed to be planted in France’s Graves district.

Wine of the Week: 2020 Dry Creek Vineyards Chenin Blanc, Clarksburg ($16) – One of the most reliable white wines produced in California from year to year, this stunning melon-scented wine offers substantially more interest than most other wines in the price range. There are hints of peach and nectarine, and the entry is lush and soft, but it also has the fresh crispness of a good acid balance. It’s especially delightful for those who don’t want the herbal notes of Sauvignon Blanc.

California is facing one of its worst droughts in history and wildfire season is fast approaching. California Farmers Union Vice President George Davis discusses what it's like working on a knife's edge and Chris Scheuring of the California Farm Bureau Federation shares the dangers that are just around the corner. Source by: Stringr

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Dan Berger lives in Sonoma County, Calif., where he publishes "Vintage Experiences," a subscription-only wine newsletter. Write to him at He is also co-host of California Wine Country with Steve Jaxon on KSRO Radio, 1350 AM.

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