The efficacy of barrier sprays to reduce the update of volatile phenols in a smoke event and the resulting sensory analysis of these wines

Abstract

Wildfires release volatile phenols (VPs) through the thermal degradation of wood lignin, and these compounds can be absorbed by grape berries, leading to smoke taint in wine. As wildfire events increase in frequency and severity, the wine industry faces growing challenges, with few effective vineyard strategies available to prevent uptake or reduce sensory impacts. This study evaluated the efficacy of two potential barrier sprays, a clay-based kaolin treatment and a polymer based film forming product (EMP), previously identified as promising in vineyard trials. Four purpose-built greenhouses over two rows of Cabernet-Sauvignon (Vitis vinifera) vines were used for controlled smoke exposure treatments. Each greenhouse contained two rows of six vines. Barrier sprays were applied 21 days before smoke exposure using a tractor-mounted sprayer at 60 g/L for kaolin and 10 g/L for EMP. Both were applied at a rate of 935 L/ha at a speed of 4 km/h. Corresponding control vines received water applications. Non-smoked control fruit was sourced from vines outside the greenhouses. Smoke exposure was conducted overnight for 10 hours using a pellet smoker with hickory pellets. Grapes were harvested 27 days later at 25 °Brix. Half of each treatment lot was washed at the winery using tap water sprayed over the grapes and a mechanical agitation prior to processing. Wines were produced using standard winemaking protocols. Sensory properties were evaluated using modified descriptive analysis, and free and total VPs in grapes and wines were quantified using gas chromatography-mass spectrometry (GC-MS). Chemical results showed that postharvest washing reduced VP concentrations in both grapes and finished wines compared to unwashed counterparts. Among treatments, kaolin combined with washing yielded the lowest VP levels. Sensory analysis supported these findings: washed kaolin-treated wines were rated closest to non-smoked controls and showed the least smoke-related attributes, while EMP and unwashed treatments retained noticeable smoky, ashy, and medicinal notes.

References

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