Wine, Wildfires, and Smoke Taint

by Gabriella M. Petrick, Ph.D.
Marie S. Curie Fellow 

As wildfires clouded the mid-day sun and turn a normally blue sky orange, wine makers in Napa Valley worried about fires ruining yet another vintage of their prestigious wines just as they were getting ready to harvest in 2020. It was not just the threat of wildfires cresting the mountains and burning vineyards that worried winemakers, but also the direction of the wind that could blow smoke into the vineyards and cause smoke taint in seemingly perfect grapes.

In 2020, winemaker Gregory Graziano reflected on the disastrous 2017 fires explaining that “Even when the fire was so far away, there were times when the smoke was so thick in the air it rained ash, blocked out the sun, and cast an eerie red darkness over us that was so dark you needed your car headlights on when driving.”

While the 2020 Glass fire destroyed houses, tasting rooms, and production facilities of at least 26 different wineries, the vineyards actually act as a firebreak. Think of the grapes as little water bombs that protect the vines, the vineyard, and sometime structures. As Chris Howell, the winemaker at Cain Vineyard, which lost buildings dating back to the 19th century, said “The undergrowth, the native grass, is typically what burns, but by now, we know that the vines themselves don’t burn.”

But even if the vines don’t burn, the grapes are damaged by the heat and smoke.

So, what is Smoke Taint?
The short answer is nobody really knows. But we know it when we taste it. Smoke taint makes wine taste like ash from a cigarette or worse, rendering the wine undrinkable. Some of the terms used to describe it are smokey, burnt, burnt rubber, ash, ashy, ashtray, cold ash, smoked salmon, smoked meats, smoked foods, salami, leather, disinfectant/hospital, medicinal, dirty, earthy. The wine is also characterized by “an excessive drying in the back-palate and retronasal ash character.”As global temperatures have risen and wildfires become more common not just in fire prone California, but in Australia, South Africa, Southern Europe and even the usually damp Pacific Northwest, the wine industry is trying to find ways to salvage fire-fouled wine.

The earliest description of smoke taint I could find was from Giacomo Grazzi-Soncini’s, 1892 book Wine: Classification, Wine Tasting, Qualities and Defects translated by Fredric Theodore Bioletti who was working at the University of California’s Agricultural Experiment Station at Berkeley at the time. Grazzi-Soncini’s was the Director of the Royal School of Viticulture and Oenology in Alba, Italy. Bioletti published it as part of the Board of State Viticulturalists 1891-1892 Biennial Report as a practical guide to determine quality wine and how to identify and remedy defects in California’s expanding wine industry.

He described a smokey tastes as:

…resemble[ing] the smell of burning wet or green wood. It is … somewhat acrid and bitter, recalling smoke and soot. …it is found more rarely in Italian wines than in German.

This defect may be occasioned by the smoke given off by ill-constructed stoves used to heat the fermenting-room or cellar; or it may be due to the unfavorable climatic conditions during the vintage.

With the smoky taste a wine will lose its brightness, become cloudy, and, if not cured by sulphuring, changes into a liquid not to be tolerated by even the most uncritical palate.

Grazzi-Soncini only alludes to wildfires in passing as “unfavorable climatic conditions during the vintage.” He seems to suggest the heat needed to support fermentation in German wineries tainted wine more than wildfires. He also distinguishes between a smokey, a burnt and a cooked flavor. But beyond Grazzi-Soncini in 1892, smoke taint seems to be missing from 20th century scientific literature.

Modern Investigations into Smoke Taint
It was Australia’s devastating 2003 fire season that brought smoke taint to crisis levels as wine makers and producers sought to save their wine. Australia suffered some of the worst wildfires in its history in 2003—Canberra in particular suffered devastating wildlife and fire tornadoes ricocheted across the bush.

This was that year the Australian Wine Research Institute (AWRI) was flooded with requests to evaluate wine for smoke taint from Victoria and New South Wales—there was nothing left of the ACT’s wine in 2003. While the AWRI only received 66 requests in 2000/1 season, 43 in 2001/2 season and 72 in 2002/3 season, in 2003 more they analyzed more than 2000 samples. They put samples through mass spectrometers to identify compounds that caused taint, but at the end of the day, it was the taste of the wine that determined if it was tainted or not.

In an interview in 2015, AWRI’s Adrian Coulter, said “We really saw it come up as a big problem in 2003, and since then it’s been a regular occurrence. Now, pretty much somewhere in Australia, every year, there’s somewhere exposed to smoke taint.”

In her 2011 Ph.D. dissertation, Kristen Renee Kennison explained that “In the few published reports of smoke taint that exist, a consistent theme of lack of scientific research on the issue is apparent.” She goes on to say that by the first decade of the 21st century wine taint was a “new phenomenon” and that “rapid research” was needed. Kennison ran a series of experiments smoking grapes to see if taint was noticeable in the wine. She found that the grapes she smoked tasted of taint. She also identified a set of compounds that were present in tainted wine. These same compounds are found in wine that is barrel-aged. Barrels are burned to varying “toasts” when they are made. These Volatile Organic Compounds or VOCs are produced when wood is burned.

Kennison suggests that guaiacol and 4-methylguaiacol are key indicator compounds that indicate wine will taste of smoke. She also found that the ripeness of the grape matters quite a bit. Before veraison—or when grapes turn from hard green little bulbs into plump, juicy grapes—smoke has little effect, but they became vulnerable to taint shortly after veraison. Grapes repeatedly exposed to smoke had stronger flavors of smoke taint. Smoke taint also increases during fermentation, so although the grape may taste perfectly fine in the field, but once it is fermented the taint flavors develop and intensify.

Intense wildfires in Washington State also spurred research on smoke taint in 2006. After a month of wildfires in the Washington’s Okanogan Valley, British Columbian wine growers were worried that those fires tainted their crops as smoke blew up the Similkamee Valley just 50 km north of the fires. Stacey I.

Sheppard and her research group at the University of British Columbia focused on determining if guaiacol and 4-Methylguaicol were a product of wildfire smoke. They found when they burned Ponderosa Pine to smoke grapevines that guaiacol settled on the grapes and was absorbed into the skin, even for very short exposures. Even one hour of exposure created smoke taint and ashy wines. In other words, it did not take long for wildfire smoke to destroy a plot, a vineyard, or even an entire wine district.

By 2015, smoke taint was such a problem for viticulturalists and winemakers that the Australian Journal of Grape and Wine Research published a review article on the state of scientific knowledge around VOCs associated with wine taint. Here the picture became more complicated. Although guaiacol and 4-Methylguaicol were thought to be biomarkers for smoke taint, sometimes these compounds were in the wine, but taint couldn’t be tasted. Also, during the fermentation process the yeast actually makes the problem worse, especially if the wine is kept on the lees—the dead yeast—for any length of time.

As smoke taint became a persistent and reoccurring problem, researchers tried a variety of remedies including washing the grapes, applying compounds, freezing, and even reverse osmosis to try to get the offending molecules out of the wine. The solution by 2015 was simply to not bring tainted grapes into winery or ferment it. While this prevents smokey wine, it had huge financial implication for both growers and winemaker causing the destruction of entire crops or vintages in particularly bad smoke years.

As long as wildfires have burned close to vineyards there has been smoke taint. Smoke taint is not a new problem, but the scale and scope of it is as wine production and consumption has globalised from late 20th century has become ever more evident. It will continue to plague the industry even as scientists make progress – and it is sobering to think that, while it is one of the most obvious aspects of the impact of heat and drought on the taste of wine, it is far from the only one.

Gabriella M. Petrick, Ph.D. received her degree from the University of Delaware as a Hagley Fellow. Her interdisciplinary research on food combines the fields of the history of technology, sensory history, environmental history and the history of science. She has also trained with the Culinary Institute of America, Cornell University and recently been a research fellow at University of Stavanger, Norway.

Sources
Gregory Graziano on the 2017 California Wildfires 
Ester Mobley, on wildfires and the California wine industry, National Geographic, 9 October 2020 .
M. O. Krstic, D. L. Johnson, and M. J. Herderich, “Review of Smoke Taint in Wine: Smoke-Derived Volatile Phenols and their Glycosidic Metabolites in Grapes and Vines as Biomarkers for Smoke Exposure and Their Role in the Sensory Perception of Smoke Taint,” Australian Society of Viticulture and Oenology 21 (2015)
Grazzi-Soncini, Wine: Classification, Wine Tasting, Qualities and Defects, translated by F. T. Bioletti, (Sacramento: California State Printing Office, 1892), 50.
[Peter Høj, Sakkie Pertorius, and Rea Blair, eds. The Australian Wine Research Institute Annual Report 2003 (Adelaide: The Australian Wine Research Institute, 2003), 37
Kristen Renee Kennison, “Smoke Derived Taint in Grapes and Wine,” Ph.D. Dissertation, Curtin University, Australia, October 2011, p. 3.
Kennison, “Smoke Derived Taint in Grapes and Wine,” p. 3.
Stacey I. Sheppard, Manpreet K. Dhesi, and Nigel J. Eggers, “Effect of Pre- and Postveraison Smoke Exposure on Guaiacol and 4-Methylguaiacol Concentration on Mature Grapes,” American Journal of Enology and Viticulture 60:1 (2009): 103.