The Complex Science and Evolving Toll of Smoke Taint

In 2020, a series of wildfires ravaged parts of Northern California and western Oregon, blanketing much of the West Coast with smoke. This came on the heels of major fire events during the previous three years that burned nearly 3.8 million acres in California alone. Meanwhile, Australia suffered devastating fires in 2019 and 2020 that affected Queensland, New South Wales, South Australia and Victoria.

Whenever there are wildfire and smoke events in wine country, after first trying to process the multitude of horrors inflicted upon those who live there, wine professionals may wonder about the impact on that year’s vintage. The effect of smoke on wine grapes is complex, so it can be hard to say.

“Just because you have smoke doesn’t mean your grapes will be smoke-impacted,” says Anita Olberholster, a researcher at University of California, Davis who studies the subject. “What we tell growers is, if there is smoke, there is a potential risk. But it’s just a potential risk. Don’t assume. It’s very difficult to predict.”

Tom Collins, who studies smoke influence in wine at Washington State University in Richland, Washington, agrees.

“It’s a complex mix of things to go from having some smoke in the vineyard to having an impact on the quality of the wine,” says Collins. “You have to look at all of the various factors to start to understand whether a particular exposure is going to result in a problem or not.”

Those factors include everything from wind speed and age of the smoke to winemaking decisions and the composition of the wine itself. In fact, even trying to evaluate the presence of smoke influence can be challenging.

What is Smoke Taint?

The effects of smoke on wine grapes can range from what’s referred to as influence or impact, which can be relatively minor. These grapes can still be used to produce wine, albeit perhaps with some corrective measures. The scale goes all the way up to smoke taint, where the wine is considered faulted.

Smoke-influenced wines can smell like mesquite smoke, tar and clove. These can range from quite subtle to overt.

“Early on in a ferment, [smoke taint] will actually smell really nice,” says Brian Rudin, winemaker at Canvasback in Walla Walla, Washington. “[It] can have a woodsy, resinous spice that’s attractive, or smells almost like Mexican chocolate. But it can become a distraction later in the wine’s life and add a layer of flavor that doesn’t belong.”

“Just because you have smoke doesn’t mean your grapes will be smoke-impacted.”—Anita Olberholster, University of California, Davis

Aromas in a smoke-tainted wine can become increasingly distinctive.

“It’s not the kind of subtle waft of a distant wood fire,” says Tim Kirk, co-owner/winemaker at Clonakilla in Australia’s Canberra District. “It’s burnt salami served on an ashtray.”

Caleb Foster, winemaker at J. Bookwalter Winery in Richland, Washington, echoes this sentiment.

“It’s like licking an ashtray or the burnt side of a cigar,” says Foster. “I tend to get [these flavors] at the tip or the tail, at the very beginning of the taste or on the finish.”

What Causes Smoke Taint?

Smoke influence in wine occurs when trees and other vegetation burn.

As much as a quarter of wood consists of a compound called lignin, a structural component that provides its strength and rigidity. When lignin burns, it creates airborne compounds, referred to as volatile phenols. These compounds can be transported over large distances. Ultimately, the compounds either degrade or settle on the ground.

This can make it hard to determine their impact.

“One of the biggest questions I get is ‘I’m X miles away from the fire. Am I safe?’ ” says Olberholster. “It’s not about distance, per se. It depends on a lot of different factors. We’ve had [vineyards] that were 100 miles away more impacted than one that was 10 miles away.”

The intensity of the smoke and the duration of the exposure contribute to any lasting effects on grapes.

Another important factor is the freshness of the smoke. The volatile compounds that cause smoke taint can potentially degrade or drop out over time and distance.

While people see smoke and worry about its potential effect, smoke’s visual presence and even the Air Quality Index are not necessarily reliable indicators of its impact on wine grapes.

“Many times when we look at smoke, what you’re seeing is particulate matter,” says Olberholster. “Particulate matter is not volatile phenols. Volatile phenols are really, really small. They aren’t even measured by particulate counters.”

Smoke in the Vineyard

Once smoke is in a vineyard, these volatile compounds can get onto grapevines and leaves, and depending upon the phase of the growing season, the berries. The latter is where the largest issues lie.

“Berries are a little bit like a sponge,” says Olberholster. “[Smoke] doesn’t stay outside the skin. It actually moves inside.”

Once volatile smoke compounds enter the berry, a chemical reaction takes place.

“When grapes are exposed to volatile smoke compounds, they absorb these compounds, and then they add sugar units to them,” says Eric Wilkes, a chemist who studies smoke taint at the Australian Wine Research Institute (AWRI).

This process is believed to be a defense mechanism, rendering these compounds less harmful to the plant, but also more difficult to detect.

The phase in the plant’s growth cycle can also make a critical difference. Research indicates that grapes are most susceptible to smoke damage in the first seven days following veraison, when grapes change their color. However, the risk remains up until harvest. Earlier smoke events can still have an effect.

“If they are the right type, it appears you can have pre-veraison exposures that can have an impact on the quality of the fruit and the wine,” says Collins.

Testing for Smoke Influence

Determining whether smoke influence is present in grapes is not simply a matter of tasting them.

“Tasting grapes tells you absolutely nothing,” says Foster. “Yummy tasting grapes can be smoked.” Rather, winemakers must rely on two tools: analytic testing and sensory evaluation.

Analytic testing is conducted by a commercial laboratory that examines the grapes, ferments the juice or both. The lab looks at between two and 13 markers that indicate potential smoke exposure, like volatile and sugar-bound compounds. However, smoke involves thousands of compounds, and the wine is in its earliest stages. So even these indicators might not tell the entire story.

“Invariably, what you’re trying to do is make an assessment based on analytics of something that is pretty much at the embryonic stage, with a view of looking at how it’s going to develop as an adult,” says Con Simos, industry development and support manager at AWRI. “That’s a real challenge.”

“Tasting grapes tells you absolutely nothing. Yummy-tasting grapes can be smoked.”—Caleb Foster, J. Bookwalter Winery

Some of these marker compounds are also found in toasted oak barrels. Once a wine touches oak, whether during fermentation or aging, it’s difficult or impossible to evaluate for smoke’s impact without a look at a broader range of compounds. Even tests on fermenting juice in stainless steel or grapes can be nuanced and may not lead to binary answers.

“We simply can’t tell someone, ‘Your fruit is going to be tainted, or your wine is going to be tainted,’ ” says Wilkes. “But what we can say is, do your grapes fall into the expected range for these compounds, or is it only a little bit above, or is it massively above? It’s really about giving people a better ability to make a risk assessment.”

Sensory Evaluation

Sensory evaluation involves doing “bucket ferments,” or small-scale fermentations, in advance of harvest, and then tasting the fermenting juice.

Doing so is fraught with issues, however. First, there are inherent challenges in trying to smell and taste juice that is actively fermenting and releasing compounds that can enhance or mask smoke aromas and flavors.

Human variables abound, too.

“There’s naturally a lot of genetic diversity in people and what they can smell and taste,” says Oregon State University’s Elizabeth Tomasino, who studies sensory aspects of smoke exposure to grapes. “About 20% of the population, they don’t taste [smoke taint] at all. But that leaves 80% that do.”

Within that 80%, sensitivity can vary by as much as a hundredfold. Foster experienced this when he poured a wine he knew to be smoke-tainted to a group of winemakers and growers. The response was varied.

“I realized in that moment, this is where it’s really hard,” says Foster. “I don’t want to go into the market where some people think it’s fine and some people don’t. And some people are going to be pissed that they just spent that money and think I lied to them.”

Finally, the composition of the wine itself can affect how smoke influence presents.

“If you have slightly different [alcohol] concentrations, that’s going to change your perception of these compounds,” says Tomasino, who adds that variety and wine style also make a difference. “We found doing this in different Pinot Noirs, we’re getting different [sensory] thresholds.”

Remediation Techniques

Once potentially smoke-impacted grapes are harvested and taken to the winery, various winemaking techniques can either limit or exacerbate any possible effects.

“The more processing that you undertake, anything that’s going to extract that juice, you’re going to get higher levels of releases of these compounds,” says AWRI’s Simos.

Hand harvesting decreases risk, as does excluding leaves and stems, minimizing time that juice ferments on the skins, restricting use of enzymes that enhance flavor or color, cooler fermentations and keeping press fractions separate.

If a wine is lightly smoke-influenced, winemakers can try fining agents, activated carbon or reverse osmosis. All approaches need to be used with caution.

“Invariably, a lot of the treatments that work, they also have an impact on the quality of the wine as well,” says Simos.

Analytic testing has its limits. Interpretation can be nuanced, and capacity can become overwhelmed during widespread disaster events.

The timing of treatment is also critical.

“If you are going to treat a wine for smoke, early in its life is better,” says Canvasback’s Rudin. “You have to be very careful that you’re not pulling away all of the wonderful flavors and textures. It’s like you have this beautiful painting, but with a fly stuck in the oil paint. We want to try to touch just that one thing.”

At higher levels or later in the process, winemakers may have little choice but to discard the wine. Even with treatment, smoke taint can potentially return as the wine ages in bottle and sugar-bound smoke compounds become liberated.

“I’d never not been able to solve a problem before,” says Foster. “I’ve made great wines from moldy grapes and from grapes with other problems. You can always do something to make wine that you can stand behind. But with smoke taint, sometimes you’ve entered a dead end.”

An Industry Under Fire

Many times, however, smoke exposure can have little or no effect on the final wines. This was the case in Washington’s 2018 vintage, when wildfire smoke filled the air for weeks during veraison and harvest. Not only did the resulting wines seem to show little impact, it was perhaps the state’s best vintage qualitatively in the last 20 years.

These sorts of complexities make decisions challenging for growers and winemakers.

“What are you going to do?” says Rudin. “If you see a little smoke in the air, you’re not going to give up and not crush grapes. It’s our job to make the best wines we can every single year, whatever the conditions are.”

Other times, when smoke is severe, the results can be ruinous. This was true for some Australian wineries during the 2019–2020 fires.

“The whole coast seemed to be on fire,” says Tim Kirk at Clonakilla in New South Wales. “Fifty to 100 kilometers away, you could see this eerie red glow.”

While the fires were distant from his winery, testing showed levels of smoke marker compounds in Kirk’s grapes 10 times the amount that most people would notice and find objectionable.

“We made the very painful decision once we’d seen enough of the analysis results coming back that we couldn’t make any wine from our vineyards or any vineyards,” says Kirk. “We just said, ‘We can’t do it.’ ”

Even analytic testing has its limits. Interpretation can be nuanced, and capacity can become overwhelmed during widespread disaster events. That occurred when smoke blanketed the entire U.S. West Coast during the 2020 harvest.

“We’re on a war footing,” said Gordon Burns, president of ETS Laboratories in St. Helena, California, in mid-September. “The areas impacted are completely unprecedented. If [wineries] need a number for the purpose of insurance coverage, we can help with that. If they’re trying to do analysis to make a harvest decision for this year, it’s unlikely that we can satisfy that need.”

Later that month, ETS’s main laboratory had to close due to wildfires in the immediate vicinity.

Testing capacity was similarly overrun in Australia last season.

“Some of the hardest emails I’ve had to send out was to customers to say you’re not going to get your results in 10 working days even though your fruit is ready to be picked now,” says Wilkes.

In the end, growers and winemakers have to determine how to proceed based on what tests say and what they taste. Consumers then have to decide if they are going to buy wines from potentially smoke-impacted vintages.

“It’s really an industry issue because nobody would knowingly sell a bad product,” says Foster, who notes that smoke-tainted wines aren’t a health hazard. “You can drink smoke-tainted wine. It’s not poison. But the question is, do we like it?”

With major wildfire events and the like increasingly common, researchers and winemakers continue to strive to better understand smoke taint. They aim to develop prevention methods in the vineyard, create remediation techniques in the winery and fine-tune testing.

Wine is a $72-billion industry in the U.S., and the financial impact of disastrous wildfires like those of the last four years is clear. Even smaller-scale events can have devastating effects on growers and wineries.

“What’s happened this year in different countries is a wakeup call to viticulture worldwide,” says Simos. “We’re really not going to get on top of climate change. It’s something we’re going to have to live with. It’s not going to go away. It’s something that people are somehow going to have to adapt to and live with and come up with some strategies to manage it.”