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SMOKE TAINT UPDATE 2018

Smoke exposed vineyards can result in smoke tainted wines with undesirable sensory aromatic and mouthfeel characteristics, which detract from overall wine quality.

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Over the past 15 years, wildfires have become increasingly more common in the dry summer months for wine growing regions all over the world. Smoke exposed vineyards can result in smoke tainted wines with undesirable sensory aromatic and mouthfeel characteristics, which detract from overall wine quality. Research has shown the compounds primarily responsible for the development of smoke tainted wines are free volatile phenols (Parker et al. 2012), which are products generated during the combustion of plants such as trees and grasses. Research has also shown that these volatile phenols can undergo biotransformation once they enter grapevines to give glycoside, or ‘bound’ forms of the phenols (Hayasaka et al. 2010). The non-volatile glycosides can be considered precursors to the volatile phenols, which are responsible for the aromas and flavors of smoke taint in wines. Two years ago Vinquiry Laboratories by Enartis introduced a robust method of analysis which provides winemakers and viticulturists data which indicates the presence and potential severity of smoke taint in their grapes or wine.

Which compounds are responsible for smoke taint?
When absorbed by the plant, smoke taint related volatile phenols become bound to sugars by enzymatic activity within the berry. These glycosylated forms of phenols are not detectable aromatically, as the glycosylation process reduces volatility of these compounds. Throughout the process of fermentation, ageing, and wine storage, these bound forms slowly hydrolyze to become “free” (volatile) and aromatically detectable. While brushfires of different types can produce smoke compounds in grapes of considerable variability, the two compounds found most commonly across all types of brushfires are Guaiacol and 4-Methyguaiacol. For the above reasons, Vinquiry Laboratories by Enartis USA offers a robust method for the quantification of Total Smoke Taint Markers (volatile and glycosylated smoke markers) in grapes, juice and wine.                                               

How can I assess the level of smoke taint in my grapes?
In grapes, we recommend measuring the Total Smoke Taint Markers as the “free” (volatile) fraction is almost non-existent with grapes and not representative of the smoke taint risk. Testing grapes two weeks prior to harvest is recommended.

How do I assess the level of smoke taint in my wine?
To assess the risk of smoke taint in wine, we recommend testing for Free and Total Smoke Taint Markers as this gives a more complete picture for the status of free and bound fractions within the wine. For red wines, samples can be tested just after pressing a red must and at any point during the ageing process.

How should I submit samples for smoke taint markers?
When testing in grapes, it is recommended to sample 2 weeks prior to the estimated date of harvest. Always take a representative sample of grapes, juice or wine and send it to Vinquiry Laboratories in Windsor, CA.
Recommended sample size - Grapes: 200 berries or 5-7 clusters. Juice or wine: 50 mL of sample

How much smoke exposure to grapes will cause a wine to be smoke tainted?
Studies have shown that in just as little as 30 minutes of exposure to heavy smoke (30% obscuration/m), at a sensitive stage of vine growth, is enough to cause a smoke effect in wine (Kennison et al. 2008). 

Should I rinse my grapes to reduce smoke taint?
Washing grapes at reception does NOT reduce the smoke taint risk (figure 1).

Recommendations for handling smoke affected grapes
Smoke taint compounds are present in grape skins and leaves, therefore their levels increase with maceration time. We recommend avoiding machine harvesting, removing leaf material, reducing skin contact, and separating press fractions.

  • Press fractions in white/rosé juice:  Press fractions for a white or rosé have higher concentrations of smoke taint markers than free run juice. Separating these fractions and testing them separately after fermentation will help minimize risk of smoke taint.
  • Skin contact in red grapes: Recent research has shown a majority of smoke related compounds are extracted within the first few days of grape soaking and fermentation. With this in mind, limiting extraction for red fermentations is not a good strategy for limiting smoke taint.

Recommendations for remediating smoke affected wines

  1. Fining agents have been shown to be effective for remediation of some volatile fractions of smoke taint in wine. For this reason, measuring the total and free levels of smoke taint markers in wine can provide information for the amount of smoke taint which still exists in a bound form in the smoke affected wine. Enartis additionally offers several fining agents which can be utilized to remove volatile smoke taint:
    • Fenol Free - activated carbon with specificity for phenol removal with low color removal capacity
    • Claril SP - blend of PVPP, potassium caseinate, and bentonite. This product has been found to improve organoleptic characteristics of smoke affected wines
    • Stab Micro - Pre-activated chitosan is able to remove vinyl phenols as well as smoke taint markers such as Guaiacol

It is highly recommend to conduct fining trials, followed by sensory evaluation, to understand the best option for each specific smoke affected wine. Analysis may also be conducted to verify changes in smoke taint markers.

  1. The bitter and ashy aftertaste associated with smoke taint compounds can be mitigated in smoke affected wines with the use of polysaccharides such as Surli Velvet and/or Citrogum or Citrogum Plus.
  1. Reverse osmosis is a physical treatment which can reduce volatile free smoke taint compounds. This process, like fining, does not remove bound forms of smoke compounds within a wine.

See our full Winemaking Guidelines for Red Wines and White Wines for recommendations on how to manage smoke tainted grapes.

For more information, please call (707) 838-6312.

 
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