Breakthrough! Sulfur-Containing Compounds Are Accurate Markers for Smoke Taint

For years, a class of compounds known as volatile phenols have been used as the sole markers for smoke taint in wine and grapes. But their efficacy wasn’t consistent. Often, wines with high levels of volatile phenols didn’t taste ashy or smoky, while wines with low levels did. With West Coast winemakers in urgent need of more reliable markers for predicting smoke taint in wines made with grapes exposed to wildfire smoke, Oregon State University enology professor Elizabeth Tomasino and her lab set out to search for other compounds that could be causing the issue.

Last fall, Elizabeth and doctoral student Jenna Fryer devised a new standard for isolating and training the palate on the smoky/ashy component of smoke taint, made of charred leek. In a tasting of the new standard with Washington State University’s Tom Collins in November, the group decided to analyze the standard for sulfur-containing compounds, known to be present in leek. In Tom’s subsequent analysis, it was confirmed: a class of sulfur-containing compounds called thiophenols were found not only in the standard but also in smoke-affected wines. These compounds were not found in wines that had not been exposed to smoke. Further sensory evaluation proved that very low concentrations of thiophenols result in smoky and ashy aromas when combined with volatile phenols.

“This is a critically important for winemakers who are increasingly dealing with the impact of wildfire smoke on their grapes,” Elizabeth said. “It provides them markers that are much more predictive of smoke taint in wine than we previously had.” The findings are not yet published, but she and Tom Collins presented them at the American Society for Enology and Viticulture national conference in San Diego this month and in a follow-up webinar organized by the West Coast Smoke Exposure Task Force.

Cole Cerrato, a postdoc in Elizabeth’s lab, confirmed the structure of the compounds using Nuclear Magnetic Resonance, an instrument that allows the molecular structure of a material to be analyzed by observing and measuring the interaction of nuclear spins when placed in a powerful magnetic field. Ongoing sensory analysis in the lab continues to validate the finding that wines are described as smoke-tainted only when these sulfur compounds are present with volatile phenols.

“This discovery changes the game, as these new compounds are a completely different class of compounds than we were previously studying,” Elizabeth said. “Much of the smoke taint mitigation work to date has not been overly successful and now we know it’s because we have been looking at the wrong thing. We should be much more successful over the next year or two in providing the industry with mitigation strategies that are actually effective.”

A $7.65 million Specialty Crop Research Initiative (SCRI) grant from the USDA’s National Institute of Food and Agriculture ensures that the work will continue. Elizabeth co-leads the project focused on the impact of smoke exposure on grapes with Tom Collins and UC Davis enologist Anita Oberholster. Its broad goal is to provide tools for the grape and wine industry to quickly make decisions about whether to harvest grapes or make wine following a smoke event. This new discovery is a big step in the right direction!

This article was adapted from the original, titled “Oregon State Researchers Discover Compounds Contributing to Smoke Taint in Wine and Grapes,” by Sean Nealon, published in the Oregon State University online newsroom, June 23, 2022.