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.

Compositional Changes in Smoke-Affected Grape Juice as a Consequence of Activated Carbon Treatment and the Impact on Phenolic Compounds and Smoke Flavor in Wine.

An increase in bushfires and wildfires globally and consequent smoke exposure of grapevines has seen an elevated need for remediation options to manage the impact of smoke taint in the wine industry. Two commercially available activated carbons (PS1300 and CASPF) were evaluated at 1, 2, and 4 g/L with juice from smoke-affected Pinot Noir and Chardonnay grapes. PS1300 and CASPF treatments removed up to 75 and 92% of the phenolic glycosides in the smoke-affected Pinot Noir rosé juice, respectively, and both carbons removed virtually all (i.e., 98-99%) of the phenolic glycosides in the smoke-affected Chardonnay juice at the highest dose rate (4 g/L). The free volatile phenols in the wines were similarly lower in concentration following treatment. Sensory analysis confirmed that the wines made from carbon fined juice had reduced smoke aroma and flavor compared to those from the nontreated controls. However, desirable sensory properties such as color and fruity attributes were also negatively affected by the treatment. The dose rate should be optimized in industry practice to find a balance between reducing the intensity of smoke-related sensory attributes while maintaining or enhancing positive attributes.