Smoke from fires can be detrimental to a crop of grapes and to the wine that is to be made from those grapes. When I was visiting California this past fall there were multiple massive fires. The smoke from these fires was widespread and lasted many days. Upon asking about the affect of the smoke on grapes some people in the industry informed me that it was not bad enough and had not lasted long enough to affect the grapes. I was skeptical so I decided to do some research.
Grapes must have passed the veraison stage of growth, where the grapes begin to ripen, for them to be impacted. Once that stage is reached, smoke, for as little as a ½ hour, can have an affect on the wine grapes. The particles that land on the grape skins will, during fermentation, turn a fine tasting grape into a smoky, ashy, burnt flavor in the wine. This ‘smoke taint’ is created by smoke compounds that bind with sugar molecules to form glycosides during the fermentation process. These glycosides break down in the acidic wine, releasing the smoke compounds and creating a smoky aroma or taste.
What is not fully known is what distance the smoke can travel without causing smoke taint. It has to do with the amount of particles present when they land on the grape. Unfortunately just washing the grapes will not improve the grapes. The compounds have already infiltrated within the grape and will only show its bad side upon fermentation.
In northern California over 85% of the harvest had already come in when the fires began. Some wineries were able to harvest immediately and thus, have perhaps saved their remaining grapes, while others have lost the vintage for the wines that were to come from those remaining grapes. However, studies have shown that only the vintage where there was smoke taint is lost. The following vintage shows no impact from the previous years smoke.
Some wineries have used reverse osmosis and/or carbon filtration to help offset smoke taint. There has been limited success with this. Additionally, the desired characteristics of the grapes become muted after these processes, leaving the resulting wine as really only useful for jug wine.
There are ongoing studies regarding smoke taint. Wildfires are becoming more prevalent and wineries are willing to invest in the research to find solutions for smoke taint. Until that time, most winemakers will forego making wine when their grapes were still on the vine when a fire and the resulting smoke from nearby fires came through their vineyards. For 2017 we might see a reduction of some wines from higher altitude places that had not already harvested by the time the fires began. But, as long as there are no fires after veraison occurs next year, they will be back.