Development and Utilization of a Model System to Evaluate the Potential of Surface Coatings for Protecting Grapes from Volatile Phenols Implicated in Smoke Taint

Due to the increasing frequency of wildfires in recent years, there is a strong need for developing mitigation strategies to manage the impact of smoke exposure of vines and occurrence of ‘smoke taint’ in wine. One plausible approach would be to prevent or inhibit the uptake of volatile phenols from smoke into grape berries in the vineyard. In this study we describe a model system we developed for evaluating under controlled conditions the effectiveness of a range of surface coatings (including existing horticultural sprays) for reducing/preventing the uptake of volatile phenols and their subsequent conversion to phenolic glycosides. Grapes were coated with the materials to be tested and then exposed to gaseous phenols, via evaporation from an aqueous solution, in a semi-closed glass container. Analysis of volatile phenols and their glycosidic grape metabolites demonstrated that the treatments typically did not provide any significant protection; in fact, some resulted in higher concentrations of these compounds in the grapes. The highest concentrations of volatile phenols and their glycosides were observed after application of oily, hydrophobic materials, suggesting that these materials may enhance the adsorption or transfer of volatile phenols into grape berries. Therefore, it is important to consider the types of sprays that are being applied in the vineyard before and during smoke events to prevent the potential of exacerbating the uptake of smoke compounds by grape berries.