Winemakers Worry Wildfires Will Leave Whiff Of Ashtray In Their Wine

This has been tough year for America's west coast vineyards. Wildfires in October in Northern California and this month in Southern California have left acres of wine country scorched and black. While California's 2017 grapes have been safely harvested already, winemakers around the world are wary about a threat that is growing along with the frequency of wildfires: smoke taint.

Smoke taint can happen when grapes are exposed to smoke. The resulting wine has an unpleasant taste, often described as ashy, burnt, and ashtray. California's growers might have lucked out this year, but significant wine regions, including in Australia, South Africa, Chile, and Portugal, have all had serious fires in recent years, and climate change is anticipated to make it worse.

Research into smoke taint is relatively new. Scientists at the Australian Wine Research Institute in Urrbrae, South Australia, began looking into it after an extremely bad fire season in 2003. That year, 1.2 million hectares (nearly three million acres) of land in northeast Victoria burned. "All of a sudden, winemakers were reporting horrible taints in wine," says Mark Krstic, AWRI's business development manager. That's when researchers made the first connection between smoke exposure and taint in the wine.

But there's still no definitive way to know if and how smoke will affect the resulting wine.

Fires produce free volatile phenols — compounds that can attach to the grape's sugars. They are difficult to smell, taste, and detect, and might later be released during fermentation, potentially showing up in wine. There are two — guaiacol and 4-methylguaiacol — that are thought to be mainly responsible for smoke taint, but scientists are still sorting that out.

Here's where it gets complicated: Some volatile phenols are naturally found in some wines, and also in oak barrels used for aging. There is no industry standard as to how much is too much.

Also, different grape varietals react differently to smoke, and the amount of smoke exposure required to taint grapes isn't known. Scientists and winemakers also believe smoke taint can develop as a wine ages. The closer the grapes are to harvest, the more susceptible they are to the compounds.

Grape growers have some commercial options to assess taint. The leading technique requires small-batch fermentation of exposed grapes, which can take a couple of weeks before the results are ready.

So researchers are searching for methods that improve accuracy and take less time.

Researchers at the University of British Columbia, Okanagan in Kelowna, B.C., have recently created a chemical test that can be used as a risk-assessment tool to detect the exact level of compounds in grapes, quickly and without fermentation. Their work was published in the Journal of Agricultural Chemistry in August.

"There are tests out there but we found them to be wanting when we reviewed the literature," says lead researcher Matthew Noestheden, a PhD candidate at UBC Okanagan. "We sort of revised the mouse trap, and we feel we have a much better approach to understanding the concentration of these compounds in the berry," he says. They looked at eight different compounds.

To test their method of detecting the phenols in grapes, Noestheden and Wesley Zandberg, UBC Okanagan assistant chemistry professor, began field trials (literally) in 2016. They set up small tents around a section of vines in a few obliging growers' vineyards in British Columbia and filled the tents with smoke. They kept tabs on the compounds in the grapes from ripening through to fermentation. Early test results show that they were able to match the concentration of compounds in the berries while they were still on the vine with the ones in the resulting wine.

They made bad wine from their smoked grapes, and they're happy about it. "When we can claim we can make a terrible tasting wine, that excites us," says Zandberg. They were able to detect the phenols in the wine with only two hours of smoke exposure on the grapes — an hour a day over two days, he says.

One of the duo's test sites is Quail's Gate, one of the oldest vineyards in British Columbia's Okanagan Valley. Smoke taint is a massive concern for the wine industry, says Quail's Gate winemaker Nikki Hallaway, and also a bit of an off-limits for discussion because no one wants their wines associated with it. "It's kind of a taboo topic because nobody really understands the how, what, why, where," she says.

She's cautious about using current techniques to mitigate taint like reverse osmosis because of the potential to remove the flavor, body, and complexity of the wine. "Any time you filter a wine to that extent, you're taking out good stuff as well as bad stuff," she says. Quail's Gate agreed to let the researchers into their vineyard because the winery is interested in new research that could help solve the problem.

Noestheden and Zandberg are looking beyond smoke taint. "Now we're going to try to connect the analytical chemistry to what a seasoned sensory analyst can actually taste," says Zandberg. In other words, they want to remove some of the subjectivity of winemaking and wine tasting, and improve understanding of desirable wine traits. "It's the same biochemistry in both grape and yeast during fermentation, so we're hoping in the long term to turn this into a clear understanding of what goes on during fermentation and how you can harness small changes in the vineyard or the winery to improve wine flavor," he says. "But that's a longer term adventure."

AWRI's Krstic cautions that while Noestheden's and Zandberg's science is sound, he thinks there needs to be more testing and positive results before winemakers will know exactly how smoke is impacting their wines.

The researchers acknowledge there's much left to be discovered. "I'm shocked daily by it," says Noestheden. "We've [been] making wine for 5,000 years, and there's still a mountain we don't know."

Danielle Beurteaux is a journalist based in New York who writes about science, technology, startups, and food. Find her on Twitter @daniellebeurt.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.