What is smoke taint?
Smoke from fires, particularly bushfires, can 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 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.
How is smoke taint measured?
Guaiacol and 4 methylguaiacol (G & 4MG) are considered good 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 analyzed 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.
What limitations are there with this test?
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 can also analyse the bound component of these compounds by hydrolysis of the conjugates.
What level of the marker compounds are acceptable?
One recent report quotes 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. 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.
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