UBCO tests for smoke taint in wine using chemical markers

Photo: UBCO

With wildfires an ongoing concern in the Okanagan and in British Columbia in general, University of British Columbia Okanagan researchers are looking at how smoke impacts the grapes used in wine-making.

Heavy smoke that frequently settles over vineyards in the Okanagan can seep into grapes and create an ashy, smoky or medicinal-tasting wine.

“This kind of research is valuable because it can provide more accurate and more regionally relevant risk assessment tools,” says Dr. Wesley Zandberg, associate professor of chemistry in the Irving K. Barber Faculty of Science.

“It can importantly help wine producers connect chemical measurements to the taste and smell of their product, and that leads to improved ways to potentially mitigate this problem and reduce smoke taint in Okanagan wines.”

Wildfire smoke will continue to impact Okanagan vineyards and those around the world, Dr. Zandberg says. The taint will vary between regions, but the study will look at how wine producers can better protect themselves from smoke-tainted wines.

The teams studied 10 Okanagan wines produced in 2018, a serious fire season. All of the wines tested were perceptibly influenced by smoke exposure. Three wines were on the market but identified as “smoke affected” and seven were never marketed because of the high levels of smoke taint detected after fermentation.

Researchers sent these tainted wines—as well as model wines deliberately fortified with carefully determined concentrations of chemicals linked to the aroma of smoke—to nine commercial and research laboratories around the world to compare concentration results and assess testing accuracy.

All nine laboratories had very similar—and accurate—results in calculating the concentrations of generally accepted markers of smoke taint like guaiacol and 4-methylguaiacol; however, they had much lower accuracies for other volatile phenols and particularly for free cresols—a class of related compounds.

The study also concluded that the laboratories were less accurate in identifying free cresols, and the calculated concentrations of these free cresols in the tainted wines varied significantly between each lab.

“It’s important to notice that just because these chemical markers of smoke taint are there and can be measured or tasted, that doesn’t mean you have a tainted product,” says Dr. Zandberg. “That’s why it’s important to distinguish between smoke-tainted and smoke-affected wine. Just because smoke can be perceived doesn’t mean necessarily the wine is tainted, since this can be subjective.”

Smoke can add to a wine's profile depending on the balance of other tastes and consumer preferences, says Dr. Zanderberg, but if the smoke taste is beyond what a majority of people would enjoy, it becomes smoke tainted.

The paper notes that some volatile phenols naturally occur at high levels in certain species of grapes like Shiraz, which is associated with a peppery taste. Guaiacol can also be present in significant levels after wine matures in oak barrels.

Judges differentiated between fruitiness and acidity and the sensory evidence of smoke exposure, like cold ash, medicinal or burnt rubber aromas and flavours, as well as an ashy aftertaste.

Interestingly, concentrations of free cresols—the same compounds that the laboratories were least accurate in identifying—were most strongly correlated to the taste and smell of smoke taint in the sensory tests.

The study has been published in the journal Molecules and included researchers at Kelowna-based Supra Research and Development and the University of Adelaide.