Understanding smoke taint

Recent bushfires have cast a pall of smoke over several winegrowing regions and maturing grapes exposed to smoke compounds may present a potential risk to quality.
Growers and winemakers should familiarise themselves with the management options for smoke-exposed fruit.

Facts Sheets from The Australian Wine Research Institute:

Facts Sheets from Department of Economic Development, Jobs, Transport and Resources (DEDJTR) Victoria – Centre for Expertise in Smoke Taint Research

Understanding Smoke taint
Professor Kerry Wilkinson, University of Adelaide, School of Agriculture, Food and Wine

During 2017, significant fires occurred in or near wine regions in the US, Canada, New Zealand and Chile, resulting in vineyard exposure to smoke, and in some instances, heat and/or fire damage to vines. Australian wine regions have largely avoided smoke or fire damage thus far this vintage, albeit recent fires in South Australia and New South Wales may have affected some grape and wine producers. Nevertheless, with the 2018 vintage underway, it seems appropriate to review the key findings from smoke taint research.

Volatile compounds present in smoke can be taken up by grapevine leaves and fruit, and depending on the timing and duration of smoke exposure, can taint wine (Kennison et al. 2009, 2011). Several volatile phenols, including guaiacol, 4-methylguaiacol, cresols and syringol, can be measured in wine, as markers of smoke taint (Hayasaka et al. 2010, Hayasaka et al. 2013). However, grapevines accumulate smoke derived volatile phenols in glycoconjugate forms, i.e. with one or more sugar molecules attached (Hayasaka et al. 2010, Dungey et al. 2011), which complicates detection of smoke taint in grapes. Hydrolysis of glycoconjugates during fermentation can release the volatile phenols into wine (Kennison et al. 2008), but a significant pool of volatile phenol glycoconjugates remains in wine (Ristic et al. 2016), even after extended bottle aging (Ristic et al. 2017).

Analytical methods which measure volatile phenol glycoconjugates have been developed to facilitate detection of smoke tainted grapes (Dungey et al. 2011, Hayasaka et al 2013). Alternatively, grapes can be harvested early, fermented and the resulting wine analysed for evidence of smoke taint; i.e. chemically to determine volatile phenol levels or by sensory analysis. Fruit maturity has been shown to influence the perception of smoke taint in wine (Ristic et al. 2015); volatile phenols have also been identified in fruit of some red grape varieties, Shiraz in particular; i.e. as natural grape constituents (Ristic et al. 2016).

To date, the most successful methods of removing smoke derived volatile phenols from tainted wine involve the addition of activated carbon (Fudge et al. 2012) or reverse osmosis and solid phase adsorption (Fudge et al. 2011). In both cases, amelioration reduced the intensity of smoke-related sensory attributes, but glycoconjugates remained in the treated wines, and may therefore continue to impart ashy palate characters (Mayr et al. 2014). Reduced skin contact time during fermentation also reduces the intensity of smoke taint in wine (Ristic et al. 2011), but isn’t practical for all wine styles.

Ongoing research aims to understand the enzymes involves in glycosylation of smoke derived volatile phenols, to evaluate the capacity for foliar sprays to provide a physical barrier against smoke exposure, and to develop new analytical methods for detecting and quantifying smoke taint in grapes and wine.

Further reading

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For further information about smoke taint support, please contact the AWRI helpdesk on (08) 8313 6600 or helpdesk@awri.com.au.