Where there’s smoke, there’s taint (maybe)
By Aaron Mandel
AWS Director of Education
With the recent fires in Northern California, there has been a lot of concern about smoke taint in wines and what the wineries can do about the problem. So, I thought a brief discussion of smoke taint might be in order.
First, the problem of smoke taint in 2017 wines is being overblown. Many of the grapes in the Napa and Sonoma vineyards had already been picked. Even those vineyard that still had grapes waiting to be picked will not necessarily have problems with smoke taint. Smoke composition, concentration, duration of exposure and variety all play a part in smoke taint.
How does taint get into the grape?
So how does some taint enter the grape? Most of the smoke taint enters the berries through the cuticles. Basically, through the waxy layer on the skin of the grape. While the volatiles that give the taint may also enter the vine through the leaves, studies show that the movement of the smoke taint through the vine itself is very slow. The closer to harvest the grapes are to ripening, the greater the risk of smoke taint. Because the smoke taint enters through the cuticle, washing the grapes before crush does little good.
Why is it hard to detect early?
The actual compounds in smoke taint are glycosides. This means that the volatile aromatics- those you can smell- are connected to sugar molecules. Since they are bound to sugars, the volatile aromas are stuck in the juice they are not wafting about the air waiting for you to pick up their smell. But the sugar bond with the volatiles can be broken. This may take place during fermentation, malolactic or during maturation. When the sugar bond is broke, the aromatics are freed. When the wine is drunk, further breakage in the bonds may occur, increasing the sensation of smoke taint. This is the reason that smoke taint can be so difficult to assess. You pick the grapes, do the crush and everything smells just fine- you escaped. Then you ferment the grapes and things start getting funky.
Wineries are currently sending out grapes for testing to determine whether their grapes will suffer smoke taint. This is often done by performing small batch fermentations with grape clusters taken from various parts of a vineyard and then performing an analysis to check on the presence of the volatile compounds that cause smoke taint.
What if the grapes have smoke taint?
So, what can the wineries do if they have smoke tainted fruit or believe there is a risk of taint?
One thing is to avoid the breaking of the skins as long as possible. The skins have many volatiles in them so limited contact might help. Hand harvesting the grapes can minimize breaking of skins as long as possible and, of course, shorter maceration can help. Whole bunch pressing and pressing in fractions also can assist.
Of course, these methods are best used with white wines where skin contact may not be required. But what about red wines? If the grapes have smoke taint, there is not a lot that can be done. Some wineries use reverse osmosis to remove smoke taint, but this method is said to only be a temporary fix and the smoke taint returns over time. Flash détente can also be used, since it removes volatile aromas and may remove some smoke taint. But Flash Détente is not 100% effective. It may remove the taint below the detection threshold of approximately 5-6 ppm if the level of smoke taint is slightly over that amount but it is not going to take a 50-ppm smoke taint level and lower it to 3. Even then, it is difficult to say what aromatic precursors in the wine may react with the smoke taint volatiles making the taint detectable at lower levels.
In the end, there is little that can be done with badly tainted grapes. Some “smoky” wines have been successfully marketed with smoke tainted grapes in the past for barbeques but the market for such wines would seem to be limited. Heavily charred oak barrels can also be used to mask the aromas, but the masking can only go so far.
At this early stage, it is impossible to say if there will be any real problem with smoke taint from the Northern California fires. I expect that a few vineyards will have smoke taint, but that the overall impact from taint will be relatively small. Fortunately, smoke taint is not something which carries over from year to year, so 2018 so not be effected from this year’s fires.
The larger concern is the effect on those working in the region. While most wineries escaped damage from the fires, whole neighborhoods were burned down. Affordable housing in Napa and Sonoma was already in short supply. The fires took lives, homes and property. The American Wine Society is raising money to help those affected by the fires. Please consider donating to the cause. In addition, please consider visiting the region. Many of the businesses in Northern California depend upon tourists. The fires cut tourism dramatically. Visiting for a few days will help those in the region get back on their feet.