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
The exposure of vineyards and grapes to smoke can result in wines with undesirable sensory characteristics, such as smoky, burnt, bacon, medicinal or ash, usually described as ‘smoke tainted’.
The compounds in smoke primarily responsible for the taint are the free volatile phenols (e.g. guaiacol, 4-methylguaiacol, o-cresol, p-cresol, m-cresol, etc). These compounds are produced and released into the atmosphere when lignin in wood is burnt. The primary mode of entry for smoke-related volatile phenols into the vine, and accumulation in the fruit, is directly via the waxy cuticle on berries. When free volatile phenols enter grape berries, they can react rapidly with grape sugars to give the glycoside ‘bound’ forms of the phenols (source).
Glycosidic bound phenols: the ticking bomb
Free volatile phenols can be absorbed directly by grapes and can bind to grape sugars to give glycosides that have no smoky aroma. Often these glycosides are described as smoke taint precursors. During fermentation (and over time in barrel or bottle) these glycosides can break apart, releasing the volatile phenols into the must or wine, and allowing the smoky flavor to be perceived. These glycosides can also release the volatile phenols in the mouth during the drinking of wine, which may contribute to the perception of smoke taint later as wine ages (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?
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
- 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
- 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
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