Sonoma, Napa vintners eye early wrap to wine grape harvest

Winemaker Alison Crowe usually expects to be picking the last of her cabernet sauvignon grapes from the coolest regions of Napa Valley in the first week or so of November.

But the wild late summer weather this year has Crowe and other vintners and growers already eyeing an earlier finish to the North Coast wine grape harvest.

“There will be more winemakers at Halloween parties this year,” said Crowe, vice president of winemaking at Plata Wine Partners in Napa.

Crowe and others in the region figure this season is running about two weeks ahead of the historical pace. Key reasons include another year of drought combined with bouts of early-season frost and late-season extreme heat.

Six days of temperatures well over 100 degrees in late August and early September sent vineyard crews and wineries across the region into overdrive.

That was followed two weeks later by an unseasonably early rain storm, which dropped an inch in a number of North Coast appellations and up to 3 inches in some areas near the coastline.

“This has not been an easy year,” said Glenn Proctor, a partner in San Rafael-based wine and grape brokerage Ciatti Co. “Hurry up and rush then stop then hurry up. There are lot of tired harvest crews and winery personnel.”

Depending on the grape variety and stage of ripening, high heat and significant rain can damage fruit or significantly change desired characteristics, so wineries may quickly adjust plans for what to pick and when.

So far this season, roughly three-quarters of the wine grapes in Sonoma County have already been picked, mostly white grapes, such as chardonnay and sauvignon blanc, plus early ripening red varieties like pinot noir and zinfandel, Proctor said. Yields for pinot noir and zinfandel have so far been lighter than earlier anticipated. The heat spike is a key culprit.

“There were decisions on picking fruit, because it was raisining, and we heard some things were picked at very high brixes,” Proctor said, referring to dehydration of grape berries to look like raisins. Brix is a viticultural measure of grape sugar content. Sparkling grapes are usually picked at levels below 20 degrees brix, and table wine grapes are harvested commonly in the mid-20s.

Much of Plata’s grape supply is in Napa County, and picking of the county’s king grape, cabernet sauvignon, is just getting underway there. Still, Crowe expects those grapes to be in by month’s end.

Ciatti and Turrentine Brokerage grape dealers heard that some fruit was coming in with sugar readings over 30 degrees brix.

VA Filtration USA in Napa and Scott Laboratories in Petaluma, which help vintners counter winemaking problems, both sent out notices just after the rainstorm, saying they were getting inquiries from wineries with sugar levels around 40. High sugars can complicate fermentation, and one method of dealing with that involves diluting the juice with water to lower sugar levels to allow for a more successful fermentation.

“There was a bottleneck of multiple varietals all coming ripe at the same time, and wineries got backed up,” said Christian Klier, Turrentine’s North Coast grape broker. “Some growers got hung out due to wineries’ capacity issues.”

But some vintners also decided to ride out the heat spike, to see if the sugar levels would come back down. Crowe called for growers with water reserves to use them on the thirsty vines to keep the berries from shriveling.

Bevill Vineyard Management, which farms about 1,200 acres in a number of Sonoma County appellations, had some remaining chardonnay, zinfandel and petite sirah blocks that went through the heat and then the rain.

The company was expecting to start picking the last major cabernet sauvignon grapes still on the vine around the beginning of October. Because of signs of dehydration, particularly for the few clusters that are sun-exposed there, it’s not known yet whether those handful of vineyard blocks will yield 500 or up to 650 tons, owner Duff Bevill said.

Klier said North Coast growers have suffered lower grape yields because of drought, frost, then extreme heat, as fewer tons per acre mean less revenue.

“It was back-to-back hits to the grape growers,” Klier said.

While the latest heat wave was extreme, it wasn’t totally unexpected, according to Steve Matthiasson of Premiere Viticultural Services in Napa.

“It was an extreme version of something we see a lot, which is a Labor Day heat spike — but not this hot,” Matthiasson said. “And so we plan in our viticulture — we plan for that all year.”

The company’s clients farm about 2,000 acres of vines mostly in Napa County, with some in Sonoma County. Matthiasson said the Labor Day heat spike has recurred in the past two decades, except for the rainy 2011 season.

Matthiasson said the industry has learned to be careful with vine leaf removal to keep shade to protect clusters from sun damage and also to retain soil moisture with greater use of compost and cover crops in the vineyard rows. In the 2010 season, foggy days in June and July prompted growers to remove vine leaves to increase airflow on the clusters to fend off mildew, but then came a heat wave in mid-August that damaged a lot of fruit.

Better shading of grape clusters on the vine was the recommendation of a new study from UC Davis. Researchers there spent the last six years trying to find ways to solve the problem of heat-damaged red wine grapes, such as cabernet sauvignon, resulting in “jarringly jam-like wines that are high in alcohol and sugar and lacking in acidity,“ according to the university news release Thursday.

The study, to be published in the journal Frontiers in Plant Science, examined different types of grapevine trellises and irrigation amounts. It concluded that growers in hot areas should move away from vertical shoot position, or VSP, trellises, one of the most common and widely used systems for training vine growth.

VSP trellises position vines to grow in vertical, narrow rows with the fruit growing lower to the ground, allowing for greater exposure to sunlight.

“We’re finding that there is no shortage of solar radiation in California. During these heat waves, these VSP trellises provide zero protection,” said lead author Kaan Kurtural, UC Davis professor of viticulture and enology and an extension specialist. “Because the fruit is low to the ground, you also get heat reflecting back into the canopy and clusters.”

The researchers found that single high-wire trellis systems allow the vine leaves to shade the grapes, because the leaves hang over the clusters, rather than the leaves being tied up vertically in VSP trellises.

The authors concluded that the reduced sunlight didn’t impact the grapes’ color or quality.

A UC Cooperative Extension vineyard adviser tackled trellis design selection and sun exposure to grapes in a 2020 lecture:

In addition to trying to time when to pick, the drought has factored into California wine grape yields this year, particularly in the North Coast, which has areas with extreme shortfalls in expected rainfall.

The 2021 wine grape harvest in the North Coast at nearly 400,000 tons was 13% below the five-year average, while California’s yield last harvest at 3.6 million tons was 6% off the average.

Higher pricing than in 2019 led to the value of the North Coast crop rebounding to $1.2 billion, following a drop in 2020 to $833 million when the wildfires cut short that year’s harvest.

Jeff Quackenbush covers wine, construction and real estate. Before coming to the Business Journal in 1999, he wrote for Bay City News Service in San Francisco. Reach him at or 707-521-4256.

Sept. 29, 2022, 1:15 p.m.: This story has been updated with research released Thursday by UC Davis on the impact of vineyard trellis design on heat damage to grapes.

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