How Smoke Taint Can Get Into Wine

With numerous wildfire outbreaks all over the world in the last few years, vineyards adjacent to these horrific blazes are having to cope with a very new problem. As if there aren't enough difficulties already within the wine industry, here is yet another one. But this is not like any of the others, it is smoke taint in wine, and causes concern to winemakers.

Most of the fires will have been started during an exceptionally hot spell of weather, or possibly a lightning strike on parched ground that has not seen rain for some time. If this is a sign of what is to come with changing weather patterns, then there are some extraordinary issues that will need to be addressed in the future - and one of them is how to rid the smoke taint from the wine.

How the smoke gets in the wine

smoke in wineSmoke taint coming from wildfires
Photo Credit: Wine Business Monthly

One only has to stand next to a fire or barbeque to come away with your clothes smelling of smoke. The garments will then have to be hung out in the open and aired to rid them of the smell. Smoke clings fast and is not easy to dispel. Getting it out of wine, which has had the smoky aroma in it since the grapes were pressed, is not straight forward. Being similar to the smoking of fish where the fillets have been hung up in a smoke filled building; the grapes in the vineyards have absorbed the smoke for some time.

Smoke tainted aromas have often been described as burnt, burn toast, burnt bacon and phenolic, not too appealing. To an extent the disagreeable qualities of the taint depend on the type of fuel being consumed by the fire. Bush fires and conifer forests have differing chemical structures to say those of open grassland fires.

If smoke is readily absorbed by the vines and grapes, then the flora of a certain wine region must also leave its imprint not only on the grapes but also on the finished wine.

Another area worthy of note is that of the toasting level of a wine barrel, and the flavour intensity which is selectively sought by winemakers. These same toasting levels impart some similar compounds into a finished wine as fire smoke does - but this is desired and controlled.

Some established scientific parameters about smoke taint in wine

  1. Grape vines, leaves and skins absorb mainly guaiacol and 4 methyl guaiacol from the smoke (as well as other compounds). It has been shown that smoke taint is not just the consequence of small fire particulates falling onto the grapes, but is more systemic. Washing the grapes vigorously or removing the waxy surface of the grape, has no effect on smoke taint present. What actually happens is that the fiery compounds penetrate right into the vines, leaves and skins.
  2. There is a variation in smoke taint between different grape varieties, Cabernet Sauvignon, Pinot Noir and Sangiovese have a high susceptibility, whereas Shiraz and Merlot are found to be less susceptible.
  3. Grapevines are most sensitive to smoke exposure from 7 days after veraison (when the skins become translucent) through to harvest time. Prior to this advanced ripening stage, the sensitivity is somewhat reduced. As the grapes ripen, the skins become lighter and thinner and therefore are more easily penetrable by smoke, so any 'damage' would be immediately prior to picking.
  4. Harvesting mechanically or by hand has a big influence on the concentration of 'total guaiacol' in the volumes of juice collected. Machine harvesting accounts for around 98% of the 'total guaiacol' coming through in the pressings and lees, while hand picking is in the region of 40%.
  5. The concentration of guaiacol in the juice increases with the maceration time, and more so if leaves are being macerated as well.
  6. 30 minutes of a single heavy exposure of smoke to grapevines is sufficient to produce smoke taint in wine, providing that the exposure has occurred during a period of high sensitivity.
  7. The smoky character does not seem to carry over from one year to the next. Grapevines that have absorbed smoke in one season do not then present the same affect in the fruit the next season.

How to remove the smokiness from the wine

Fining agents have been used, mostly without success apart from activated charcoal. The use of charcoal pre-fermentation to reduce guaiacol concentration is effective at rates of 1.0 g/l to 1.6 g/l.

A process called 'Reverse Osmosis' can be used to remove compounds from wine. Some compounds can be cleaned from the filtrate, and the remaining wine then returned back into the system. As guaiacol is a fairly small compound with small molecules it can be removed, but other larger compounds which have not been removed can easily dominate the aroma.

If the smoke taint in the wine is low, this removal method is ideal as only one or two passes are necessary. However, heavily tainted wines requiring several passes run the risk of having some of the fruit characters removed as well as the taint.

Results from reverse osmosis treatment of red wines have shown a noticeable reduction in the concentration of guaiacol by roughly one third, and tests are on-going. While the fires no doubt will continue to burn, research is helping the wine industry to cope with the problem of smoke taint in wine.

Rob Hemphill has been a professional winemaker for over 20 years, and is now a freelance marketing writer living in the UK. He specializes in wine consultancy and has a wide knowledge in vines, vineyards and wine growing techniques as well. His favorite varietals are Gewurztraminer and Shiraz.

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Article Source: How Smoke Taint Can Get Into Wine

By Rob Hemphill