Influence of berry skin cuticular wax on smoke-derived volatile phenol uptake in grapes

Abstract

Wildfire smoke exposure is known to alter grape composition and cause “smoke taint” in the resulting wines, causing significant economic losses (USD 3.7B in the US in 2020). Moreover, rising fire intensity and duration due to climate change are increasing the relevance of smoke exposure across viticultural regions worldwide, including Portugal, Spain, and Chile. While the chemical nature and sensory implications of smoke-derived volatile phenols (VPs) have been widely reported in the literature, comparatively less attention has been given to the role of grape berry skin properties in modulating smoke compound uptake. This study examined the role of cuticular wax quantity and composition in influencing the uptake of smoke-derived compounds by grapes. Seven grape genotypes characterized by differing berry skin wax were selected for controlled smoke exposure experiments. Grape clusters and individual berries were separated into four treatments in a factorial design defined by cuticular wax status (intact or removed using chloroform) and smoke exposure (present or absent). Berries and clusters were exposed to artificial smoke under controlled conditions at two phenological stages of maturity. Volatile phenols (VPs) in grapes were quantified by GC–MS/MS. Cuticular wax was determined gravimetrically and chemically characterized, after derivatization, by GC–MS/MS. Grape berry skin and tissue morphology and thickness were also evaluated using scanning electron microscopy (SEM) and light microscopy (LM). Smoke exposure increased VPs concentrations across all genotypes and sample types (WAX or NO WAX). In particular, smoke-exposed berries differentiated according to wax presence, abundance and composition, clearly highlighting the protective role of cuticular wax against volatile phenols (VPs) uptake. These findings identify cuticular wax influencing grape response to smoke exposure and provide new insights into genetic variability in smoke taint susceptibility, with implications for vineyard risk assessment and mitigation strategies under increasing wildfire pressure.