Review of smoke taint in wine: smoke-derived volatile phenols and their glycosidic metabolites in grapes and vines as biomarkers for smoke exposure and their role in the sensory perception of smoke taint

In recent years, the exposure of vineyards and grapes to smoke from bushfires and controlled burn events has in some instances resulted in wines described as smoke tainted. Such wines are characterised by undesirable sensory characters described as smoky, burnt, ash, smoky bacon, medicinal and ashtray. This review summarises the knowledge about the composition of smoke from forest and grass fires, describes relationships between smoke exposure of vineyards and smoke taint in wine, and outlines strategies for managing and reducing the risk to producing smoke-affected wines. The sensitivity of grapes and vines at different phenological stages to the uptake of contaminants from smoke, especially smoke-derived volatile phenols, is outlined, and the pathways for entry and metabolic transformation of volatile phenols are discussed. The potential for translocation of phenolic contaminants within the grapevine and the differences in uptake of smoke contaminants of different grape cultivars are also discussed, along with preliminary work on dose/response relationships regarding concentration and duration of exposure and subsequent expression of smoke taint in wine. The chemical basis of smoke taint in wine is described, and the relationship between volatile phenols from combustion of wood/lignin and their glycosides, and sensory panel ratings of smoke attributes in affected wines is discussed. This includes a summary of sensory reconstitution studies and measurement of flavour compounds released from nonvolatile glycosides in mouth and during in vitro model experiments, which corroborate the sensory contribution of glycosylated phenolic substances and their role as flavour precursors. Finally, the review also discusses analytical methods used to quantify free volatile phenolic substances and their associated glycosides, biomarkers for identifying smoke exposure of grapes, and strategies for assessing the risk of quality loss post-smoke exposure. Case studies are presented that outline the influence of harvesting and winemaking practices on the expression of smoke taint, and that describe oenological approaches to ameliorate smoke taint in wine.