Six Misconceptions About Smoke Taint

What research has shown about making wine with smoke-affected grapes

by Jim Gordon
wine california fires wildfires wineries vineyards mendocino sonoma smoke taint
Clusters of Cabernet Sauvignon hang in a smoky vineyard in the Rutherford appellation of Napa Valley on Oct. 10.

San Rafael, Calif.—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.

Smoke taint is not yet well understood in the wine industry, so growers and winemakers have plenty of questions about how and when to harvest the remaining grapes and how to manage fermentation and aging to diminish the potential effects of exposure to smoke. Organizations from the University of California, Davis, to wine industry laboratories and fermentation product suppliers have been actively sharing their best advice over the past week.

While fire-affected wine regions had already harvested a substantial majority of their crops before the onset of the fires, it is not too late to apply the most current knowledge about smoke taint to the remaining amount, estimated at between 10% and 25% in various counties.

Here are six 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.”




Posted on 10.17.2017 - 11:52:03 PST
To elaborate there is one study from 2008 that evaluated the process of a large multinational company which is unaffiliated with us.

It found that glcyoconjugated precursors could result in smoke taint sensory character becoming detectable again in the future. Because of this, we recommend that all effected wines be fermented dry.

Further, we recommend not to return treated wines to barrel. Volatile phenols are among the contributors to sensory smoke characters. ALL barrels have some background volatile phenol producing microbial activity. And the sensory thresholds in the case of smoke are magnitudes lower than for Brett/Dekkera. This is why we recommend treatment late and not returning to barrel.

Additionally, our methods have never been the same as the company studied. And ours have evolved dramatically since the study published in 2008.

Bob Kreisher
President, Mavrik North America

Posted on 10.17.2017 - 12:22:11 PST
Also, on the question of when grapes are most sensitive. Here in CA we've seen smoke taint result from two different scenarios.

In 2008, the fires started early (June 21) and continued well into August. Enormous tracts of land were blanketed in mild to moderate smoke for weeks. This resulted in widespread mild to severe smoke taint.

Other events have been smaller/shorter. For example, the Middletown fire of 2015 (September 12) resulted in smoke taint for one vineyard the fire burned up to (and even slightly into). But just a few miles away vineyards were unaffected.

The catastrophic fires we've experienced this year are a fundamentally unique beast, at least for California. Research does suggest that the vulnerability is significant (for grapes still hanging).

Our experience has been inconsistent. The smoke is certainly widespread. However, in comparison to 2008 it will still be (we hope) relatively brief.

Bob Kreisher, Mavrik North America