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Smoke taint
The arson attacks of recent days bring to mind one of the great problems of viticulture today: global warming, which is increasingly triggering fires of various sizes, sometimes considerable.
Consider the fire that in August 2015 devoured nearly a million acres in Washington, Oregon, Idaho and Canada.
The smoke released by the fires had also affected the vineyards and the grapes, generating in the wine what would later become famous as smoke taint.
Smoke taint
Lo smoke taintIt's much more than just a hint of smoke, as it can also be felt in the mouth.
It has been described with adjectives such as “smoky”, “dirty”, “burnt”, with a retronasal sensation of ash that lingers on the palate for a long time.
The problem was first detected in Australia during the 2003 grape harvest, when bushfires in January and February in Victoria and New South Wales forced the downgrading or disposal of thousands of tonnes of grapes, worth around AUD$7 million.
The responsibles
The studies showed that the compounds directly responsible for thesmoke taintThey are guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol and eugenol, although the presence of other less obvious compounds cannot yet be excluded.
The two most common compounds are guaiacol and 4-methylguaiacol, which are marker compounds and can therefore be indicative of smoke taint levels in grapes and wine.
Critical period
The severity of the damage depends on the quantity of smoke, its permanence but above all on the period in which the plant is exposed to it, which becomes of maximum impact if it concerns the days between veraison and harvest.
The Merlot Experiment
In 2008, the Journal of Agricultural and Food Chemistry reported an experiment conducted on Merlot in Australia in which the plants were exposed to 8 successive applications of smoke, each lasting 30 seconds, between the veraison period and the harvest.
We then proceeded to microvinifications which were then also analysed with regards to the evolution of volatile phenols:
It turned out that volatile phenols were irrelevant.
However, their concentration increased significantly during fermentation, with the highest levels detected in wines.
Initial Australian investigations have suggested that guaiacol and 4-methylguaiacol accumulate in the skins, rather than the pulp, of smoke-affected grapes. This would explain the increased concentration of these substances during fermentation following the extraction of compounds from the skins.
However, upon second glance it was noted that the concentration continued to increase even after the must had been separated from the skins and even during malolactic fermentation.
This implies the presence of one or more precursors.
Solutions
Among the possible solutions to eliminate this problem, the most used at the moment involves a selective clarification of the wine (aimed at adsorbing the compounds responsible for this organoleptic deviation) followed by filtration.
However, since it is possible that low molecular weight compounds – such as those responsible for the positive aromas of wine – are involved in this type of treatment (causing an “organoleptic impoverishment” of the treated wine), current studies are investigating the effects of filtration and clarification on a wider number of volatile compounds in wine.
Among the first to attempt to patent machinery to solve this problem was the Australian David Wollan, one of the world's leading experts on smoke taint who is now a technical consultant for Memstar.
Curiosity
The creativity of the Troon Vineyard company in Oregon's Applegate Valley managed to make the most of the disruption caused by the fire that hit the area in 2002.
The company drew attention to the smoke-affected Cabernet Sauvignon grapes by bottling a wine called Biscuit Fire Reserve.
Today this has become a collector's wine worth over $ .700,00per bottle.
For further reading:
Smoke Taint – Australian Wine Research Team
Smoke-derived taint in wine: the release of smoke-derived volatile phenols during fermentation of Merlot juice following grapevine exposure to smoke
Analysis and Amelioration of Smoke Taint by Dr. Kelly Wilkinson, University of Adelaide