As you all know, the Napa and Sonoma wine regions experienced terrible wildfires during the first half of October last year. Fortunately for wineries, about 90% of the 2017 had been harvested. But what about the remaining 10%?
Some growers dropped their remaining fruit, choosing to come back next year. Many harvested the remaining fruit, and are attempting to make good wine from it. Can they?
From Australia’s experience with wildfires and from additional studies there, we know that grapes are especially susceptible to exposure to smoke from veraison right through to harvest. Exposure to intense smoke for as little as 30 minutes left the smoke taint chemicals 4-methyl guaiacol, 4-ethylguaiacol and 4-ethylphenol at levels easily recognized by taste. The grapes in much of the Napa Valley were exposed to heavy smoke for 10 days or more.
Some winemakers have tried washing of the grapes prior to destemming/crushing as a way to reduce the impact of smoke exposure. This will greatly reduce surface ash, but will not reduce the absorbed smoke taint.
Grapes grown a bit further from the areas of most severe smoke exposure can also be problematic. Grapes themselves may taste O.K. after a mild smoke exposure because some of the offensive tasting chemicals are chemically bound while the grapes are growing. However, they are partially released during fermentation, so problems can arise after a lot of expensive processing has occurred. And even if a palate cannot taste smoke after fermentation, additional chemicals are freed from their “bound” state during aging, so a wine that is decent tasting after fermentation can turn bad after a couple of years of aging.
Six days after the fires started I drove through some of the Napa valley floor vineyards, found and tasted some not yet harvested grapes. They definitely had a smoky taste to them. I hope they and many others like them do not make it into the 2017 vintage.
(Refs.: K. R. Kennison and others)