By Bryan Tudhope of VA Filtration USA
It’s been a fiery 2015 to date, with numerous wildfires burning very close to vineyards from Southern California to the Canadian border. This has left huge swaths of acrid smoke over many thousands of acres of land. Satellite imagery has shown just how massive these smoke plumes have been.
This article serves to present the facts regarding smoke taint and offers potential solutions for dealing with the problem. For those wanting more information on the exact mechanisms of smoke taint adsorption, detection and dealing with the fruit, there are some references listed at the end of this article.
What is Smoke Taint?
Smoke taint is made up of numerous compounds present in smoke that in simplistic terms enters the fruit via the skin. The markers for smoke taint are generally Guaiacol and 4-Methylguaiacol and these can be measured in the juice prior to fermentation. It must be noted, however, that these markers do not necessarily indicate the extent of the problem but are used to identify a potential issue with the fruit. Often smoke taint is not detectable based on a sensory evaluation of squashed grapes.
Smoke taint compounds are bound to the glycosides within the grape via a glycosidic bond. During fermentation these bonds break as the glycosides are converted to their fermented by-products: ethanol, CO2, acetic acid etc. During this bond breakage, the smoke compounds are released into the wine resulting in an increase in smoke taint related volatiles, which are then easily identifiable via a sensory evaluation of the wine. Interestingly enough if one was to take a measurement of the guaicaol concentration before, during and after fermentation, one would see a steady rise in these levels. This was evident in 2009.
The levels of taint are typically much higher in red wines than in white wines. The evidence points to a concentration of the smoke compounds within the skin of the fruit. Since red wine requires extended skin contact, it is reasonable that these wines would see higher levels of taint.
Treatments for Smoke Taint
It has been shown that membranes treatment in combination with adsorption is an effective means of dealing with smoke taint – see Fudge, A. L.; Ristic, R.; Wollan, D.; Wilkinson, K. L. (2011) Amelioration of smoke taint in wine by reverse osmosis and solid phase adsorption. Aust. J. Grape Wine Res. 17 (2): 41-48.
The experience gleaned from 2009 fires was phenomenal in dealing with the issue of smoke taint. At one facility, where over 500,000 gallons was treated in multiple lots of wine, approximately half of the wine treated showed no sign of smoke taint within one year of processing. The other half showed smoke taint at levels that were a lot lower than the original levels but were still detectable! There is also anecdotal evidence that indicates treatment is more affective later in a wines life. This might be due to a slow-down in glycoside breakdown as the wine ages. Theoretically at that point, the process of smoke taint removal would be more effective and limit the chance of a reoccurrence. There is no hard evidence to back this theory but it was definitely a trend when dealing with the 2008 harvest smoke taint issues.
Other methods including additives or fining agents, have not been found to be effective.
If you want to barrel age the wine, I strongly suggest using neutral oak barrels for aging purposes. Toasted oak barrels add a smoky component to the wine that exacerbates the perceived levels of smoke taint.
For those of you with no alternative but to get the wine to bottle and on the shelf, treatment will be necessary early in the wines life.
The Treatment Process
The most effective process of treating smoke tainted wine involves the use of nanofiltration membrane elements in combination with adsorption resin. Typically the wine needs to be passed through this process at least 2-4 times depending on the severity of the problem. In 2009 wine required an average of 3 passes through the system, although some wines took 6 or 7 passes to reach undetectable levels.
References and further reading material