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Assessing The Risk That Napa and Sonoma Fires Pose For Smoke Taint

By Charles Olken

Early in the history of this blog, we often reprinted articles that were of particular educational value. Over time, as we have slowed down our blogging, so have we gotten away from celebrating the very good writing in other blogs.

The recent fires here in northern California wine country have caused incredible damage to people and property—and now that the fires are all but gone and life is slowly returning to some semblance of normal for most folks here, it is time to look forward a bit and talk about the effects on our wines.

Let’s start with this: the bulk of wine from the 2017 harvest here in California will experience no impact. Much of California wine is grown well away from the areas where the fires burned. Those wines will feel zero impact. And for the 80% or so of grapes harvested before the fires and safely tucked away in wineries that were not impacted, those wines will be unchanged. But, for the fruit that was hanging, mostly late-picked reds, those grapes that felt the impact of smoke and ash are likely to experience some level of smoke taint damage.

The other day, Jim Gordon, writing in Wines and Vines, the renowned industry-oriented publication summarized the situation well, and it is repeated here with appreciation to Jim for his lucid, careful recitation of known facts and grounded scientific theory:

“Grapegrowers in Northern California wine regions struck by wildfires since Oct. 8 have found it difficult to get the last of their crops off the vines and delivered to wineries, due to road closures, evacuated employees, power outages and other challenges. Winemakers have an additional worry about how widespread smoke may affect the quality of wines made from those last loads of grapes. The major concern is smoke taint, a consequence of smoke seeping into the pores of grape skins and grapevine leaves and becoming bound up in the juice and wine chemistry. The taint shows up later in smoky or ashy wine aromas and can taste smoky, bitter and charred.

Here are misconceptions about smoke taint to be aware of:

Misconception 1) Smoke is less of a risk late in the growing season
A study by the Australian Wine Research Institute found that taint was the most elevated when smoke exposure occurred in the period from seven days after véraison to the harvest date. California wildfires clearly erupted in that time period. Precision-agriculture firm Fruition Sciences goes further on its blog: “The nearer the fruit is to harvest, the higher the risk associated with smoke exposure.” Eric Herve of ETS Laboratories adds: “It is advisable to harvest as soon as safely possible, as grapes will keep passively adsorbing smoke volatile organic compounds as long as smoke is present.”

Misconception 2) Washing the grapes can manage smoke taint
While washing grapes could remove ash from their exteriors before fermentation, the compounds that cause smoke taint are already inside the grapes. A bulletin from the UC Davis Department of Viticulture and Enology states that “smoke-derived volatile phenols can be absorbed both directly via the berry cuticle and via the leaves and translocated to the fruit.” They note that removing leaves from the vines following smoke exposure “can reduce the severity of smoke taint in grapes and wine, but washing the grapes prior to processing has no impact on potential smoke taint development.”

Misconception 3) Smoke can affect next year’s crop, too
Numerous sources and studies confirm that smoke taint does not linger in the plant in a way that could affect the quality of future harvests.

Misconception 4) Reverse osmosis permanently removes smoke taint
Reverse osmosis is a form of membrane filtration that can remove smoke-derived compounds, but the taint returns over time “due to the hydrolysis of glycoconjugated precursors, which are not removed during treatment,” the UC Davis bulletin states. Basically, the smoke effects are temporarily bound up in the chemistry of the wine but can be released as the wine ages. Some dispute this conclusion, including Bob Kreisher of Mavrik North America, who says, “Membrane methods have come a long way since then.”

Misconception 5) Fining is an effective solution for smoke-tainted wine
Fining can effectively “clean” the smoke taint out of a wine, but fining is not a very selective process, so it will also remove many favorable attributes from a wine along with the smoke-derived compounds, the bulletin states. Fining could be counterproductive to use on potentially high-quality wines.

Misconception 6) Smoke taint in a wine diminishes as the wine ages
On the contrary, smoke taint is likely to increase with time. Industry supplier Scott Laboratories recommends on its website numerous treatments to mitigate smoke taint but adds, “Smoke-related characteristics can evolve over time, so early consumption is recommended whenever possible.”

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by Charlie Olken
Posted on:10/31/2017 8:52:27 PM

l received a number of personal emails about this article and all but one were very complimentary. One was not and I want to be sure that the record is clear.

Most of the grapes in the area of the fires were picked and crushed before the fires. There is no way that the resulting wines will suffer from smoke taint. I thought the article said that but one winery owner disagreed. It should be clear now.


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