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Grapes of Ash: How smokey air is polluting California’s wines

Phil Crews at his Pelican Ranch Winery in Scotts Valley. Crews, an organic chemist at UC Santa Cruz, showed that a method pioneered in Australia can detect smoke's impact on California wines.
Jerimiah Oetting
Phil Crews at his Pelican Ranch Winery in Scotts Valley. Crews, an organic chemist at UC Santa Cruz, showed that a method pioneered in Australia can detect smoke's impact on California wines.

Winemakers in California are facing another hot summer of drought and potential wildfire. When forests burn near California’s wine country, it’s not just the flames that threaten vineyards — it’s also the smoke, which can sully grapes on the vine that then produce ashy, bitter wine.

Now, scientists in Santa Cruz are helping winemakers sniff out the smoke impact in grapes, to better predict if the grapes are worth bottling, or better left to rot on the vine.

Like elsewhere in California,wildfires have become more destructive and common in wine country over the last decade.

That was especially true In 2020, when the catastrophic wildfire season led winemakers to cancel over $600 million in contracts with grape growers over fears that the smoke-exposed fruit would produce unsellable wine.

“It’s a huge problem for the wine industry,” said Prudy Foxx, a viticulturist in the Santa Cruz Mountains.

Foxx said that labs that test wine for impurities struggled to keep up with demand in 2020, and returned results to winemakers that were often vague and hard to interpret.

Sometimes, the results were misleading.

One of Foxx's clients — who she wanted to keep anonymous due to reputational risks — received results from a local lab that indicated their pinot noir grapes were smoke impacted.

The client ignored the result, and the wine went on to receive a wine critics’ score of 95, putting it in the highest bracket on standard 100-point wine review scales.

“There’s no detectable smoke impact in that wine,” she said. “It’s beautiful.”

Phil Crews is an organic chemist at UC Santa Cruz, and the owner of the Pelican Ranch Winery in Scotts Valley. He argues that the labs were doing the wrong measurement altogether.

“They didn't want to go the extra step,” he said. “But the data they were giving back, in my opinion, was worthless.”

Crews looked to Australia, where winemakers have struggled with smoke impact in wine for nearly two decades. He applied a method pioneered by the Australian Wine Research Institute to California wines.

That method is unique, he said, because it provides a more accurate measurement of the smoke particles that lead to smoke taint.

When grapes absorb smoke, the smokey particles bind with sugars. The smoke is so locked up with sugar, Crews says the grapes don't even smell smokey.

That all changes once the juice hits the drinker's mouth. The enzymes in saliva that break apart food tear those smoke-and-sugar molecules apart, freeing the smoke particles and causing a bitter, ashy taste.

Crews said an expensive piece of machinery, called a mass spectrometer, can "sniff out" those smoke-and-sugar molecules directly. He argues it's the best way to know if wine will taste smokey.

“I knew how to do it, but couldn’t quite do it in my research lab,” he said. “So eventually I teamed up with the SC Labs people.”

SC Laboratories is a private lab in Santa Cruz that tests another California crop: cannabis.

Jeff Gray is the company’s CEO and founder. He said SC Labs has tested cannabis in California for over 12 years. The company now has labs in both Oregon and Colorado.

“Cannabis and wine are produced in the same areas,” Gray said. “And unfortunately, they’re subject to the same environmental factors. Wildfires are now the norm here in California.”

Testing wine isn’t a core focus of the lab. But because they had the equipment and expertise that Crews needed for his study, Gray saw an opportunity to try out something new.

Vials of smoke tainted wine in the first stages of smoke analysis at SC Labs
Jerimiah Oetting
Vials of smoke tainted wine in the first stages of smoke analysis at SC Labs

“I think that we're just kind of scratching the surface,” said Paul Dorenbach, a senior analyst at SC Labs. He said they’ve measured over 250 samples from vintages between 2017 and 2021. The samples came from eight different wine varietals across 21 wine growing regions in California.

“As we test and geo-locate those samples, we can get a library of baseline levels for all of these wines,” he said, giving winemakers a sense of the impact, between unnoticeable to undrinkable.

The methods and results from the study were published in March, and are available for free. Crews said he wanted to create an open-source way for more labs to replicate the analysis, so the wine industry is better prepared for the next big wildfire year.

“We want to have a lot of labs doing this rather than one or two,” Crews said. Right now, SC Labs is just one of three labs in the world doing this analysis, he said.

Prudy Foxx, the grape whisperer, said that in the end, wine all comes down to taste — and what wine critics think.

“We're going to learn a lot about how this wine goes through the market,” she said. “If the critics choose to kibosh anything where they even detect smoke impact, that will affect the industry."

But Foxx said that wine is also endlessly complex, and a light smoke impact might add another interesting layer — a memorial to that year’s fires. Or, a bitter reminder that the wrath of climate change is growing heavier with every vintage.

Jerimiah Oetting is KAZU’s news director. Prior to his career in public media, he was a field biologist with the U.S. Forest Service and National Park Service.