CORVALLIS, Ore. — As wildfire seasons grow longer and hotter across the West, scientists are gaining a better understanding of how smoke-filled skies affect wine quality.

Researchers have detected a new class of compounds in winegrapes exposed to smoke, known as thiophenols, linked to unpleasant burnt or ashy flavors in finished wines. 

The recently published findings are part of a federally funded project led by experts at Oregon State University, Washington State University and the University of California-Davis examining how wildfire smoke impacts wine — and what growers can do about it. 

Elizabeth Tomasino, an associate professor of enology at OSU, said the discovery “provides a new chemical marker for smoke taint that could provide a reliable way to identify smoke taint and ways to potentially eliminate it during the winemaking process.” 

In the past, winemakers have leaned on another class of organic compounds, called volatile phenols, to indicate the presence of smoke taint.

Volatile phenols are found in smoke from forest and grass fires, and can be absorbed directly into the skin of winegrapes. 

However, Tomasino said the presence of volatile phenols haven’t always been a good indicator of smoke taint. For example, she said wines with high levels of the compounds often tasted fine, while others with lower levels were tainted. 

That led her team to search for other compounds that could be causing the problem. 

Cole Cerrato, a senior researcher at OSU who works closely with Tomasino, said sensory panels were asked to taste smoke-impacted wines and identify different flavors. The results could then be compared to a chemical analysis showing which compounds are present in the wines, searching for matches. 

But the team needed something to give panelists a tasting standard for “ashy” compounds.

“One of the struggles that we have had in the smoke and wine research is trying to find ways to describe these flavors,” Cerrato said. “Ash has always been a difficult one, because it’s always contaminated with other things.” 

It was Jenna Fryer, a postdoctoral scholar in Tomasino’s lab, who came up with the idea of using charred leeks. 

“She was making her apartment smell absolutely awful, putting her oven on broil and baking leeks,” Cerrato said. 

Leeks and smoke-tainted wine were sent to Tom Collins’ lab at WSU for a chemical analysis, which confirmed the presence of thiophenols in both samples. 

Thiophenols are similar to volatile phenols, Cerrato said. The sulfur-containing compounds are not normally found in wine, but rather meat and fish. They are described as tasting meaty or burnt, and just a small concentration can have a big effect on flavor.

“Humans are very sensitive to sulfur,” Cerrato said. “A little bit goes a long way.” 

Once volatile phenols are become incorporated into winegrapes, Cerrato said they can undergo a secondary or tertiary chemical reaction whereby oxygen is swapped for sulfur, becoming thiophenols.  

With a correlation identified between the compounds and smoke-tainted wine, Cerrato said the team is now focused on helping winemakers come up with mitigation strategies. 

“I describe this as like treating a disease,” he said. “We should be able to reduce that ashy, smoky component. This gives us a definite target that we can start focusing on.” 

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