Smoke taint in wine – what now?

Abstract

The frequency of bushfires close to wine regions around the world has increased in the last two decades. the economic losses incurred when grapes and wines are discarded due to ‘smoke taint’ are substantial (i.e., hundreds of millions of dollars). efforts to mitigate and ameliorate smoke taint are therefore crucial. chardonnay, rosé and cabernet sauvignon wines made from grapes exposed to smoke during the 2020 wildfires in eastern australia were subjected to various amelioration techniques: the addition of activated carbons, molecularly imprinted polymers (mips), and a proprietary resin (either directly, or following membrane filtration); spinning cone column (scc) distillation; and finally, transformation into vinegar. volatile phenols (vps) and their glycoconjugates were measured as markers of smoke taint by gc-ms and hplc-ms/ms, respectively, while descriptive analysis evaluated the intensity of smoke-related sensory attributes of wine and vinegar samples. the efficacy of three activated carbons at removing free and glycosylated vps without detrimental effects on colour or wine aroma was demonstrated. the carbons removed >50%, 35–52%, 7–20% of vps, and 10–20%, 5–10% and 0% of vp glycoconjugates from rosé, cabernet sauvignon and chardonnay wines, respectively. during scc distillation of smoke-tainted red wines, free and glycosylated vps were concentrated in the resulting ‘strip wine’; with only a small proportion of vps detected in condensate. thus, scc distillation alone cannot remediate smoke taint. in a subsequent trial, the ‘strip wines’ obtained from scc distillation were treated with activated carbon before blending with their corresponding condensates. the intensity of smoke-related sensory attributes perceived in reconstituted wines was significantly diminished compared to untreated wines. results suggest scc distillation may offer a novel strategy for remediation when used in combination with adsorbents. the addition of mips to smoke-tainted wine achieved up to 60% removal of vps, but <10% removal of vp glycoconjugates, irrespective of whether mip treatments involved direct addition to wine or passage of wine through a mip-packed column. the most effective treatment involved mip addition post-inoculation, (rather than addition during or post-fermentation), albeit some impact on wine colour and aroma was also evident. treatments of smoke-tainted wines with a proprietary resin showed promising results, achieving up to 90% removal of vps and up to 30% removal of vp glycoconjugates. when resin treatments were applied to permeate derived from membrane filtration (using a 5 kda molecular weight cut-off ultrafiltration membrane) a significant proportion of vps were removed from permeate fraction, i.e., 95–100% for chardonnay, 52–95% for rosé, and 65–95% for cabernet sauvignon. lastly, the potential for smoke-tainted wine to be transformed into vinegar was evaluated. fermentation of smoke-tainted wines by acetic acid bacteria occurred over 11 months, during which time vp glycoconjugates decreased by >76% in all vinegars. vps concentrations decreased the most in cabernet sauvignon ferments, followed by chardonnay and rosé. however, the perceived intensity of smoky and ashy notes was the lowest in the rosé vinegar, which instead exhibited tropical and cooked fruit characters. the cabernet sauvignon vinegar had prominent berry and plum flavours but retained smoky notes and an ashy aftertaste. chardonnay vinegar exhibited spice and confectionary notes and was liked the most by consumers (n=50). in summary, this project demonstrated the efficacy of different strategies for amelioration of smoke-tainted wine. the choice (and success) of the treatment will ultimately depend on the extent to which wine is tainted, but the cost of harvesting and processing smoke-affected grapes (vs. simply discarding tainted grapes) should be considered in evaluating the economic return of remediation.