Smoke and Grape – the Smoke Taint Repercussions

We received a large number of requests asking for practical information and scientific articles on making wine with smoke tainted grapes. Considering the devastation caused by northern California fires, we decided to share all the information we have collected regarding the effects of smoke on grapes and wine. We hope this note will provide some helpful hints and guidelines in a time of distress.

A few considerations on smoke taint

When vineyards and grapes are exposed to smoke, it can result in wines with undesirable sensory characteristics. ‘Smoke tainted’ wines display aromas such as burnt rubber, bacon, disinfectant or ash. Lignin, a phenolic compound present in wood, is responsible for the taint. Free volatile phenols (e.g. guaiacol, 4-methylguaiacol, o-cresol, p-cresol, m-cresol, etc) are released into the atmosphere when lignin is burnt. The main mode of entry for smoke-related volatile phenols is directly via the waxy cuticle on berries. After entering grape berries, free volatile phenols can react with grape sugars and give the glycoside ‘bound’ forms of the phenols (source).

Glycosidic bound phenols: the ticking bomb

Following direct absorption by grapes, free volatile phenols can bind to grape sugars. They give glycosides, which are non gaseous and have no smoky aroma. However, phenols bound glycosides can revert to a gaseous form at a later stage. During fermentation or during barrel or bottle aging, they can break apart and release volatile phenols into the must or wine, making smoke tainted aromas perceptible. Ultimately, glycosides can also release volatile phenols in the mouth. Thus, saliva through its pH, temperature or bacteria content can reveal or accentuate  smoke taint aromas during the drinking of wine  (source).

Sensitivity to smoke exposure

The effects of smoke  vary depending on stage of grapevine growth and development when smoke exposure occurs. The nearer the fruit is to harvest the higher the risk associated with smoke exposure. Grapevine varieties differ in their sensitivity to the uptake of smoke taint compounds. Semillon or Sangiovese for instance are more sensitive than Cabernet Sauvignon (source).

What to do in practice?

During winemaking

As fruit is being transformed into wine, a few tips on practical management from  harvest to winemaking operations have been listed here

Table 1. Summary of techniques to reduce smoke-related aromas, flavors and compounds during handling and processing of grapes and wine (adapted from Brodison et al, 2013).

In the vineyard

Research has demonstrated there is no carry-over of phenols and their metabolites from one season to the next. However, vineyard exposure to high temperatures may have long term effects.

• To assess the potential for vine survival, a simple check consists of making a small cut with a knife to expose the tissue. As shown in Figure 1, undamaged trunk tissue remains moist and green, damaged tissue appears dry and pale and dead tissue is brown and dry.

 

Figure 1 :  Undamaged (left), damaged (middle) and dead vine (right). Adapted from John Whitting.

• The inflorescence initials within the buds may have been damaged by the fires. Consequently, vines may not return to full cropping levels for several years after fires and this may benefit the vine by giving it time to recover and regrow damaged tissue. For those reasons, pruning decisions on how to get the vine back into best conditions for production next year may benefit from a bud fruitfulness assessment (source).

Practical resources regarding smoke taint

Useful links about vine and smoke

• How does smoke enter into the vine ?
• What can be done to identify and reduce smoke effect in grape and wine production?

Useful links about wine and smoke

• Washington: A note on smoke taint ; Grape vines exposed to smoke
• California: Grape affected by smoke taint ; Smoke taint in grape and wines ; UC Davis Smoke taint
• Oregon: Measures for mitigating smoke taint
• Australia : Smoke taint

Scientific references on smoke taint

Recent articles:

•  Review of smoke taint in wine: smoke-derived volatile phenols and their glycosidic metabolites in grapes and vines as biomarkers for smoke exposure and their role in the sensory perception of smoke taint.
• Effect of smoke in grape and wine production 
•  Seeing through smoke

Older articles:

• Effect of timing and duration of grapevine exposure to smoke on the composition and sensory properties of wine
• Effect of smoke application to field-grown Merlot grapevines at key phenological growth stages on wine sensory and chemical properties
• Guaiacol and 4-methylguaiacol accumulate in wines made from smoke-affected fruit because of hydrolysis
• Comparison of methods for the analysis of smoke related phenols and their conjugates in grapes and wine
• The effect of winemaking techniques on the intensity of smoke taint in wine
• 
Amelioration of smoke taint in wine by reverse osmosis and solid phase adsorption