« Smoky » is a rare flavour that can describe both a white and red wine. But where does it come from? Following the recent forest fires, can you buy Californian wine from the 2015 vintage? An Australian study provides some tips.
In this study, a vineyard experiment was conducted with four varieties (Chardonnay, Sauvignon Blanc, Syrah and Merlot) in two different ways: some grapes were regularly exposed to smoke, while others were not disturbed during growth. To be honest, the experiment leaved us with some doubts, but the conclusions are quite interesting – even considering our objections at the end of the article.
Smoke taint in wine was chemically isolated by researchers as several molecules: guaiacol, methylguaiacol, phenols (expressed as syringol and methylsyringol) and molecules of cresol (p-cresol, m-cresol, o- cresol). It is the glycoconjugates structures of these molecules (combination of sugars and a protein or a lipid) that, after vinification, become volatile and impart a smoky smell to the wines concerned.
If you don’t understand the gibberish of the preceding paragraph, it is very normal. Just remember that these molecules are revealed only after winemaking. As a result, the researchers did not just study the effect of smoke exposure to the grapes; they also vinified them to study the presence of these molecules. They furthermore conducted a series of studies on the berries (weight, size, sugar content, pH, etc.) to complement the extensive chemical studies on the wine. They harvested the grapes at two different stage to explore the effects in terms of maturity.
- No significant difference in sugar content was found between wines with grapes exposed to smoke and those that weren’t
- Berry weight and size was not affected by smoke exposure
- Smoke exposure didn’t result in any changes to the anthocyanins or phenols. The colour of wine wasn’t impaired by smoke either
- Naturally, wines exposed to smoke contained all the volatile molecules associated with causing smoke taint in high levels
Sensory results (tasting panels) per variety:
Chardonnay harvested earlier shows no characteristics of smoke on the palate, whether it was exposed to smoke or not. However, the ones harvested later was fully saturated with smoke taint, described as “ashy” by the tasters.
Sauvignon Blanc, whether harvested early or later, absorbed the smoke, leading to an ashy taste. Sauvignon Blanc harvested earlier was considered the white wine most affected by exposure to smoke in aromatic terms.
Red wines appear to be more sensitive to smoke than white wines, impacting their aromatic potential. The Merlot harvested earlier, tasters noted smoky, ashy and medicinal flavours, but, more importantly, the fruity flavours were significantly decreased. For the ones harvested later it was the same story, but slightly less pronounced, with less smoke taint and slightly more fruit.
Syrah grapes harvested earlier was described as « moderately smoky”. For the second part of the harvest, characteristics are slightly more pronounced, but remain moderate when compared to Merlot.
It is clear that the ripeness of the grapes at harvest time has an effect in the assimilation of smoke taint. Overall, white varieties seem much less affected by smoke exposure.
This study offers an interesting analysis of the problem in regions like Australia and California, where forest fires are frequent. However, this study doesn’t give much scientific explanation but rather a holistic approach to a problem that often worries winemakers from the warmest regions. Nevertheless, we further research should be conducted to better understand all the ins and outs of smoke taint in wine.
One important thing to consider is that the molecules responsible for this taste are only revealed after vinification. The only way to know if a wine has smoke taint before the harvest is to conduct a « mini » fermentation – like that which was conducted for the experiment – and analyse the wine. Needless to say that the study is not very useful from this perspective…
Furthermore, the study suggests no evolution of these aromas after ageing. Some wines can obtain a smoky flavour after ageing in casks or barrels, depending on the toasting used by the cooper. Conversely, can a wine exposed to smoke lose those smoky aromas during and after ageing? Not impossible, but unverifiable.
You can thus buy wine from California even if a forest fire occurred at the edge of the blocks. However, we would recommend to buy a white wine, like Chardonnay, preferably harvested early to limit the risk. For the rest, their might be some impact as the study showcases so be aware of it and the best remains to test it yourself: science doesn’t have all the answers yet!
Download the study by clicking on this link