Wildfire smoke: An emerging threat to West Coast wines

In August 2013, Ron and Cheryl Harms were eagerly anticipating the third harvest from their boutique vineyard in the Sierra Foothills when the massive, fast-moving Rim Fire zigzagged perilously close to their property.

The couple’s four-acre Yosemite Cellars vineyard sits on a rocky hillside surrounded by forest about 20 miles west of Yosemite National Park. From their perch high above the valley, the Harms watched helplessly as planes released flame retardant around the gathering firestorm and thick clouds of smoke settled on their ripening grapes.

“Once we convinced ourselves that we were probably going to be okay, personally, and that our property was going to be okay, it was fascinating to just see where the fire was going and how it was being fought,” said Ron Harms.

Fascinating yet terrifying, said Cheryl Harms, fighting back tears. “I have PTSD from it,” she said.

The Rim Fire, at the time California’s third-largest wildfire, torched more than a quarter of a million acres of Sierra forestland, including nearly 80,000 acres in Yosemite. The inferno spared the Harms’ home and vineyard. But it left the couple grappling with a grape affliction that has emerged as the West Coast wine industry’s latest scourge: smoke taint.

“Our grapes were very smoky,” said Cheryl Harms. When they had juice from their grapes analyzed, she said, “it was smokier than anything they’d ever tested.”

And there was little they could do to remove the taint.

Wildfires can cause extensive damage throughout the agricultural industry, destroying crops and killing livestock. But grapes appear to be the only commodity affected by smoke taint.

Winemakers intentionally add subtle smoky notes to increase the complexity of wines by aging them in toasted oak barrels. But wildfire smoke can make wines undrinkable. Smoke-tainted wines have unpleasant aromas often described as disinfectant or burnt rubber and taste “like licking an ashtray,” experts say.

“Imagine being a 5-year-old who thinks it’s fun to put dad’s old cigarette in their mouth,” said Anita Oberholster, an enology extension specialist who studies smoke taint at the University of California, Davis. Smoke taint, like sucking on a cigarette butt, assaults the back of your throat with a trademark campfire smoke or ashtray quality, she said. “The only thing I’ve ever seen that gives you that character is smoke exposure.”

Smoke taint can ruin a wine as surely as a bad cork. And as climate change increases the likelihood of drought-fueled conflagrations in fire-prone California, wildfire’s effects on grape quality have emerged as one of the biggest threats to the state’s $43 billion wine industry.

“The pandemic was an enormous challenge,” said John Aguirre, president of the California Association of Winegrape Growers. “But now, without question, I think the threat of wildfire in many different ways is the greatest challenge of the day for the industry.”

Rising global temperatures have made droughts and heatwaves more common and intense, fueling ever more devastating wildfires. Last year, thousands of drought-primed fires scorched more than 4 million acres in California—close to 40% of the national total—making 2020 the state’s largest wildfire season on record.

Still in the throes of severe drought, nearly a million and a half acres have already burned in the state this year, according to the California Department of Forestry and Fire Protection, or Cal Fire.

After several devastating fire seasons, many California vintners and wineries found themselves either denied fire insurance because they were too risky or priced out of coverage as rates skyrocketed.

Wildfires can cause serious economic losses through direct damage to vineyards and wineries. But vineyards tend to be fairly resistant to the flames, Aguirre said.

“In wine country vineyards have demonstrated themselves to be good fire breaks. They can really help prevent the movement of fire,” he said. “But the smoke is a problem.”

Losses incurred from smoke drifting into vineyards before harvest far outweigh direct losses from fires, industry analysts say.

With fire season already in high gear, scientists are scrambling to help growers figure out how to protect their harvests.

Adapting to the new normal

Scientists first recognized wildfire smoke’s growing threat to wine grapes less than two decades ago, around the same time climate change was driving more and more destructive fires.

The devastating 2003 Canberra bushfires in southeastern Australia followed one of the most severe droughts on record, and left winegrowing regions shrouded in smoke for weeks.

Inundated by inquiries for help from wineries and grape growers, the Australian Wine Research Institute ran experimental trials to understand the nature and extent of the problem.

Few vineyards sustained fire damage, the institute found, but damage from smoke exposure was widespread. Institute scientists identified compounds associated with smoke taint’s hallmark ashtray qualities. But solutions, they concluded, “remain elusive.”

“Historically, Australia had the brunt of the wildfires,” said Oberholster of UC Davis. “And now since 2017, the West Coast is in the same boat.”

In 2017, California endured “one of the deadliest and most destructive fire seasons in modern history,” according to Cal Fire. Fewer fires burned the following year, but they tore through hundreds of thousands more acres to cause some of the worst destruction ever seen.

Devastating firestorms were no longer an anomaly in wine country, but the new norm.

As Ron Harms looked out his window in early July, he could see smoke on the horizon. “It’s from the Dixie Fire, I presume, though there are also some fires in Yosemite that might be contributing to that,” he said.

The Dixie Fire, now California’s second-largest fire on record, incinerated most of the small Sierra Nevada town of Greenville a few weeks ago, and has barely slowed down.

There’s little Harms can do about the smoke, he said. “Our reality as a grower and wine producer is that we just have to roll with it.”

After yet another record-breaking fire season in 2020, wine grape growers suffered substantial economic losses due to concerns about smoke exposure. An estimated 165,000 to 325,000 tons of California wine grapes went unharvested last year, contributing to more than $600 million in losses from wildfire and smoke, according to an analysis released in July by the California Association of Winegrape Growers and Allied Grape Growers.

Many wineries rejected growers’ wine grapes, the analysis found, “often with little evidence to support the rejection and without basis in the grape purchase contract.”

A major problem stemmed from fuzzy language in contracts about “quality standards.” Contracts drawn up before severe wildfires had become a recurring wine country hazard did not mention smoke exposure. More recent contracts referenced “smoke taint” or “smoke compounds,” without clear definitions or evaluation criteria.

“The lack of understanding and science around smoke issues has meant that people are acting very conservatively and rejecting grapes,” Aguirre said. “The purpose of our report is to highlight that, regrettably, some of these actions by wineries were just inconsistent with contracts.”

Wildfires are contributing in a substantial way to economic losses in the industry, Aguirre added. “And we’ve got to change the way we’re doing things.”

Toward that end, Aguirre and other industry leaders from California, Oregon and Washington formed the West Coast Smoke Exposure Task Force to advocate for federal funding for research on managing smoke.

The task force won a $2 million grant to support smoke exposure research last year from the U.S. Department of Agriculture’s Agricultural Research Service, and expects an additional $5 million for research when the 2022 federal appropriations bill passes. The hope is to find ways to predict the risk of smoke taint in the vineyard and mitigate its effects in the winery.

“We’re optimistic that funding for research will help a great deal,” Aguirre said.

Dissecting smoke’s effects

UC Davis’ Oberholster is among the scientists leading that research. One of her top priorities will be to identify objective markers of smoke-affected grapes. The task is complicated by the fact that some of the same chemical compounds associated with taint occur naturally in berries at levels that vary among grape varieties.

Some of the growers’ contracts talk about “elevated” levels, Oberholster said. But to know what’s elevated, you need to know what’s normal. “We need to figure out a baseline for each variety to figure out what’s normal,” she said.

Concentrations of the compounds vary seasonally, so it will take multiple seasons to get an accurate picture of what’s normal. Australian scientists identified markers for their top 12 varieties, but it took them seven years because wildfire smoke kept interfering with their efforts.

Oberholster had been studying a grapevine virus in an experimental Napa vineyard when the 2017 firestorms broke out. She couldn’t get to her plot for 10 days, as wildfire smoke settled on her vineyard.

“That’s when my smoke exposure research started,” she said.

The first thing she did was review Australian studies to see if they’d identified winemaking techniques that could rescue exposed grapes. But she found no long-term solutions. Plus, studies of the effects of Australian bushfires are not generally applicable to those along the West Coast.

So Oberholster started identifying smoke-related compounds that could be monitored during winemaking and potentially affect the wine’s aromas and flavors.

Burned vegetation releases numerous compounds called volatile phenols, which travel through the air and land on grapevines and fruit. The compounds infiltrate the skin of the grapes, where they quickly bind to sugars, forming molecules called glycosides. It’s the unbound, or “free,” form that produces the off-putting aromas and flavors of smoke taint. As long as the phenols are bound as glycosides, they go undetected.

But the ratio of free to bound forms of the compounds can change throughout the life of a wine, Oberholster said, complicating efforts to predict and shape a wine’s fate. “If you’re only analyzing ‘free,’ you may not see anything that makes you worry,” Oberholster said.

When smoke-exposed grapes are pressed to release the juice to make wine, the compounds enter the juice. Red wines are most at risk of taint because the skins are left in the juice to extract tannins and color. As wine ferments, glycoside bonds break down, releasing the funky volatile phenols again.

Oberholster and her colleagues monitored more than 30 bound compounds, including eight that hadn’t been identified before, and showed that most of the reactions that produce the offensive form happen during the first half of fermentation.

This process continues as the wine ages, and even, it appears, in a person’s mouth. Bacterial enzymes in saliva can release the unsavory smoky flavors and aromas, a 2014 study found. “There was only one study,” Oberholster said. “We really need to do more work on this.”

Wine treatments can ameliorate some of the smoky traits, but only for moderately affected wines, Oberholster said.

She’s now trying to find ways to detect smoke taint in the vineyard that don’t require a battery of complex chemical analyses.

Studies have shown that grapes can acquire smoke taint in just half an hour if they’re exposed between a week after veraison, the onset of ripening, and harvest, a window that differs with the grape variety but typically spans August to October.

The good news is that smoke-related compounds don’t survive the winter. The bad news is that wildfires are increasingly happening when grapes may be most susceptible.

“During the Rim Fire it was intensely smoky in our vineyard day after day after day, during the time when the fruit was going through veraison, turning from green to purple, when the skin is really susceptible to smoke particles,” Harms said. “And here we are with our first significant smoke in the last several days. And where are we in the growing season? We’re in veraison.”

Back in 2013, when the couple realized they couldn’t remove the smoke taint from their grapes, they decided on a risky strategy. “We sat down with our family of winemakers and came up with the idea to dilute the smokiness,” said Cheryl Harms.

They harvested the exposed fruit and blended it with wine from the previous year that was still in barrels. “We made the assessment to see if we could find a wine that strikes a balance between being like having an ashtray in your mouth and having a unique flavor profile that some people might enjoy,” Ron Harms said. “We had no idea whether it would work or not.”

They ended up bottling 240 cases of Rim Fire Red. And though reactions were mixed—customers either liked it or they didn’t—the couple sold every case. Those who liked it compared the flavor to a peaty scotch.

People still call asking if there’s “any of that smoky wine left,” Ron Harms said. But he has no desire to repeat the experiment.

Sierra Foothills winemakers have long labored under the shadow of their high-end counterparts in Napa and Sonoma. Harms thinks wine lovers would be pleasantly surprised by the quality of the wines produced in the foothills.

As the Harms brace for the long fire season ahead, now with their sons in charge, they hope their south-facing vineyard above Yosemite Valley will help the French varietals they grow put their best fruit forward. And they’re counting on scientists to help them avoid making another Rim Fire Red.