Exploring Variation in Grape and Wine Volatile Phenol Glycoconjugates to Improve Evaluation of Smoke Taint Risk

Abstract

Drier growing seasons and warmer temperatures arising from climate change have intensified the duration, frequency, and scale of wildfires around the world (Bowman et al. 2020). In California, seven of the 10 largest wildfires since 1932 occurred in 2017, 2018, and 2020 (as reported on the CAL FIRE website, www.fire.ca.gov); the 2019/2020 Australian bushfire season was also one of the most devastating on record (Abram et al. 2021). When fires occur, the thermal degradation of lignin in plant material produces volatile phenols (VP) such as guaiacol and 4-methylguaiacol (Maga 1988). VPs can also be found in wines due to their natural presence in grapes (Ristic et al. 2016, Coulter et al. 2022, extraction from oak barrels during wine maturation (Pollnitz et al. 2004), and/or contamination from grapevine exposure to wildfire smoke (Kennison et al. 2007). The latter instigates risk of smoke taint, in which the sensory profiles of wines made from smoke-exposed grapes are characterized by unpleasant 'smoky, ' 'burnt,' 'drying,' 'cold ash,' and 'medicinal' attributes (Kennison et al. 2007, Parker et al. 2012.The quantitation of VPs using gas chromatography-mass spectrometry (GC-MS) is well-established (Pollnitz et al. 2004, Hayasaka et al. 2010a, 2013, but using this metric alone to predict the risk of smoke taint in wine following processing and fermentation of potentially smoke-affected grapes has been impeded by several factors. First, the