What is smoke taint?
Smoke from fires, particularly bushfires, may affect the flavour of grapes. The impact of smoke on grapes and the resultant wine varies considerably and a lot of research is being done at the moment to better understand this important issue.
Wine made from grapes that have been smoke affected have been described as having some of the following attributes: “burnt” “ashtray” “charred” “salami” “disinfectant” etc. Wine can be unfit for sale if the smoke taint is too great.
When are grapes most susceptible to smoke taint?
The time of the season is critical for the impact that smoke uptake can cause. Grapes have a low to medium uptake potential in the early stages of the season. However from around 7 days post veraison until harvest the uptake of smoke into grapes is at its highest. The exact levels and duration of exposure to smoke that will cause taint has still not been precisely determined.
How is smoke taint measured?
Volatile phenols, Guaiacol and 4 methylguaiacol (G & 4MG) are the recommended marker compounds for smoke taint. These are measured by Gas Chromatography Mass Spectrometry (GCMS) at part per billion (ppb) levels, with a detection limit of 1 ppb. Research has indicated that most tasters can detect the presence of guaiacol in a dry white wine at the 6 ppb level.
In one study four wines were analysed by GCMS for smoke taint compounds. G & 4MG were found in the wines made from the “smoked” grapes, but were not detected in the wines made from the “unsmoked” grapes.
One major issue is that these compounds can be bound in juice and wine in the form of glycosidic conjugates. If only the free portion is measured then this may be an underestimation of the potential problem. During fermentation of the juice and subsequent ageing of the wine, more of these compounds can be released and so the effect of smoke taint can increase.
Vintessential recommends analysing both the free and bound component of these compounds to fully assess the samples.
When should grapes be analysed?
The most suitable time to sample and analyse grape samples is closest to harvest as possible, when the berries have sufficient ripeness to enable fermentation.
It may also be beneficial for the winemaker to conduct small scale ferments to conduct a sensory assessment.
What sample is required?
500g representative sample of berries or a sulfured 100mL juice sample are required
What level of the marker compounds are acceptable?
Anecdotal evidence from winemakers stating that guaiacol was a good marker for smoke taint and that most tasters could detect the presence of guaiacol in a dry white wine at the 6 ppb level, and 23 ppb in red wine. The report did recommend that further work needs to be done to ascertain if this threshold level was relevant for all grape varieties. A lot of research is being done at the moment to try to better understand the problem.
Download the Vintessential Smoke Taint Fact Sheet
Find out more about our Smoke Taint Tests
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