What’s the impact of smoke on wine? UC Davis researchers are trying to find out

At an 11-acre vineyard in Oakville, UC Davis researchers are seeking a more complete understanding of smoke impact and climate change in an era of increased risk.|

Smoke taint

When wood burns, volatile phenols are produced and these compounds are primarily responsible for smoke taint. They can be absorbed by grapes and create an unpleasant aromas and flavors. Some wine experts use the descriptor of “wet ash” to describe smoke taint.

In addition to the research on smoke taint, there are many other experiments at the UC Davis vineyard in Oakville. Among them:

A recent study on trellises (structures to support vines) is a breakthrough for cabernet sauvignon and other varietals struggling with high temperatures. The six-year study, published in the journal “Frontiers in Plant Science,” found that a single 5 1/2 foot trellis outperforms the shorter, more commonly used vertical-shoot-position trellises, which begin 3 feet off the ground. The taller trellis allows the vine leaves to shade the grapes, while producing higher yields.

Another study in progress is conducting shade cloth trials with different colors — some black, pearl and blue — to keep the vines cooler and protect the grapes from high temperatures.

Yet another ongoing experiment is comparing traditional north-south vine row orientation with a newer version of east-west rows to control sunlight.

During the catastrophic wildfires of 2017, smoke inundated vineyards across Wine Country, covering vines in a thick, noxious haze.

Vintners were frantic about how their grapes would be affected, remembered Anita Oberholster, an extension specialist in enology with UC Davis.

“Suddenly, everybody wanted to know everything about smoke,” she said. “Everybody started calling me and asking me, ‘What’s the impact of smoke? What should I be doing?’”

At the time, Oberholster had limited information to guide them. The latest research then on smoke’s impact on grapes came from Australia, which had battled perplexing firestorms.

But that research focused on syrah grapes, widely grown in Australia. It didn’t translate to our region, where farmers grow a broad variety of grapes.

“It was like putting a Band-Aid on a festering wound without antiseptic,” she said of efforts to deal with smoke’s effect here in 2017.

So today, at an 11-acre vineyard in Oakville, Oberholster and other researchers are experimenting, trying to measure the impact of smoke and devise ways to mitigate it, along with the effects of drought and climate change.

Equipped with a $7.8-million federal grant, Oberholster is optimistic the research will yield actionable results.

With more information, in three to five years vintners, growers and crop insurance companies will be able to avoid the chaos and confusion they experienced in 2020 during the LNU Lightning Complex fires, she said.

Those fires began Aug. 17 that year, when most vintners still had fruit on their vines.

Some sent their grapes to labs to be tested for smoke impact, and labs became overrun with requests, forcing many vintners to make decisions in the dark, without having their fruit analyzed.

Looking for results

For grape growing, the Oakville vineyard is valuable real estate, situated in the highly esteemed To Kalon area, with the Mayacamas Mountains as its backdrop.

The To Kalon is arguably California’s most important grape-growing land. Some even call it Napa’s “first growth” vineyards, highly prized vineyards that are seen as first-class, rivaling the most valued growing areas in France. The neighbor of the UC Davis vineyard is Opus One Winery, known for its highly touted Bordeaux red blend which sells for nearly $400 a bottle.

Oberholster is joined in the vineyard by several other UC Davis professionals working on an assortment of experiments and primarily studying climate change. Most are endeavoring to find ways to protect vines from rising temperatures.

Shade cloths cover some vines, while plastic shelters others. And there’s a range of trellis structures varying in height and orientation, that support growing vines.

Oberholster, clad in a black jacket, black jeans and dusty black boots, pointed to a sensor attached to a trellis post near a vine. With an array of electronic devices on it spanning approximately 3 feet, the sensor can track volatile phenols (compounds in smoke) for a 1-mile radius.

Smoke taint can happen when grapes absorb volatile phenols in smoke, imparting undesirable aromas and flavors in wine. Some wine experts use the descriptor “wet ash” to describe smoke taint.

There are 13 sensors scattered throughout Sonoma County and Napa Valley and dozens more operating in Washington state and Oregon in collaboration with researchers there. There is eagerness for answers.

“People keep asking me, ‘What are the results? What are the findings?’” Oberholster said. “We don’t have results yet.”

Oberholster said the network of sensors is key. Over time, it will make it much easier to assess risk from smoke exposure so vintners can make informed decisions. And at low levels of smoke impact, there will be steps people can take in the winery and in the vineyard to reduce the risk of smoke taint.

“That’s a given,” Oberholster said. “We’re working on it. But I don’t think a magic bullet exists. If you’re going to be surrounded by a fire, I don’t think we’ll be able to do something to completely reverse it. I don’t want to set expectations that high.”

Grapes rejected in 2020

With more information, Oberholster is determined to protect vintners from the chaos they experienced in 2020.

Sangiacomo Family Wines, based in Sonoma, began the 2020 harvest with 5,300 tons of grapes on the vine. At the onset of the LNU Lightning Complex fires, they still had 4,300 tons yet to pick.

“Our nerves have been tested through decades of harvests, but 2020 stretched the limits,” said Steve Sangiacomo, a third-generation partner in his family’s business. “We have dealt with difficult harvests, but the smoke issue was something that really left us defenseless.”

The winery sells grapes to more than 50 wineries, and 15 rejected their pinot noir grapes in 2020 over concerns about smoke taint.

“We were aligned with our winery clients to not make wine from any grapes affected from smoke,” Sangiacomo said. “Quality is of the upmost importance, and we wouldn’t compromise it.”

Meanwhile, on the other side of the Sonoma County, vintner Raghni Naidu’s 4-acre pinot noir vineyard in Sebastopol was engulfed in smoke.

“The vineyard was at least two weeks from being ready to harvest, and it would have had to sit in that smoke until it naturally dissipated,” Naidu said.

“The fruit was tested and it came back with the possibility of smoke taint being low to minimum. But I didn’t want to risk bringing a smoke-tainted wine to my customers. ... It was actually heartbreaking, as it was also the year Naidu Wines was launched.”

Like Naidu and Sangiacomo, many others in Sonoma County decided to forgo their 2020 vintage for many bottlings. The fear among these vintners that smoke exposure would potentially malign the image of their brands factored into a steep decline of fruit harvested in 2020.

Pinot noir saw one of the most dramatic downturns, with nearly 20,000 tons less fruit harvested than in 2019 and 2021, according to the Sonoma County Grape Crop Report. Cabernet sauvignon also revealed a drop of 10,000 to 15,000 tons in 2020 compared to 2019 and 2021 levels.

“There were probably grapes left on the vine that should have been harvested,” Oberholster said. “And there were probably grapes that shouldn’t have been harvested that were. The decisions were based on perceptions, and those aren’t good guidelines.”

Pellegrini Olivet Lane, based in Santa Rosa, was one of the wineries caught up in the confusion over whether or not to harvest its smoke-impacted grapes.

When the fires hit in August 2020, the winery hadn’t begun to harvest its roughly 100 tons of grapes on the vine, according to Alexia Pellegrini, general manager and owner. The winery also had eight contracts in place to sell wine, but two were eventually rejected.

“Because of the lack of timely (smoke-impact) testing and a foggy understanding of those results, it was the wild west of winery-generated contract amendments,” Pellegrini said.

Cause for optimism

Creating clear guidelines with smoke exposure is Oberholster’s fundamental goal and the core of her research.

Her funding, awarded in January, covers the collaboration between Oberholster and other researchers at Oregon State University and Washington State University.

“We’re working together and also with atmospheric scientists on air samples,” Oberholster said. “And then we’re taking grapes and analyzing their volatile phenols.”

The aim, she said, is to amass data from sensors each of the researchers are monitoring and then create bookends: on one end, a baseline, and on the other, a threshold for risk.

“Can we develop a sensor that says yes or no to risk?” she asked. “So if you have a yes, there’s some risk and you’ll have to get a lab test. But this will allow those who really need a test to have access to a lab.”

The instruments used in the lab to analyze smoke impact of free volative phenols are extremely expensive, ranging from $150,000 to $350,000, Oberholster said.

“A lot of people tested (their grapes) who shouldn’t have tested,” he said. “And some people tested over and over again.”

But with more information, there’s cause for optimism.

“I would say every year the communication and the conversation between wineries and growers and insurance companies is getting better because people are getting more educated,” Oberholster said.

“My job is to do the science and give people information. My narrative continues to be, ‘Make the best wine you can.’”

Wine writer Peg Melnik can be reached at peg.melnik@pressdemocrat.com or 707-521-5310.

Smoke taint

When wood burns, volatile phenols are produced and these compounds are primarily responsible for smoke taint. They can be absorbed by grapes and create an unpleasant aromas and flavors. Some wine experts use the descriptor of “wet ash” to describe smoke taint.

In addition to the research on smoke taint, there are many other experiments at the UC Davis vineyard in Oakville. Among them:

A recent study on trellises (structures to support vines) is a breakthrough for cabernet sauvignon and other varietals struggling with high temperatures. The six-year study, published in the journal “Frontiers in Plant Science,” found that a single 5 1/2 foot trellis outperforms the shorter, more commonly used vertical-shoot-position trellises, which begin 3 feet off the ground. The taller trellis allows the vine leaves to shade the grapes, while producing higher yields.

Another study in progress is conducting shade cloth trials with different colors — some black, pearl and blue — to keep the vines cooler and protect the grapes from high temperatures.

Yet another ongoing experiment is comparing traditional north-south vine row orientation with a newer version of east-west rows to control sunlight.

Peg Melnik

Wine, The Press Democrat

Northern California is cradled in vines; it’s Wine County at its best in America. My job is to help you make the most of this intriguing, agrarian patch of civilization by inviting you to partake in the wine culture – the events, the bottlings and the fun. This is a space to explore wine, what you care about or don’t know about yet.

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