Winemaking with fruit exposed to smoke
Forest fires and exposure of grapes to smoke have become a major winemaking issue. The key compounds responsible for the aromas are volatile
phenols, guaiacol, 4-methyl-guaiacol, and many others, and are found on the outer (cuticle) layer of the grape. The smoke taint compounds exist
in juice and grapes in the glycosylated form. Winemaking practices can release the odorous free volatile phenols, as can time and subsequent
acid hydrolysis. Juice may taste acceptable, but during fermentation and over time may develop more serious smoke impact issues.
There are a number of winemaking techniques that can be used to reduce the effects of smoke in wines, and these are more valuable when used
in combination. The following recommendations are based on current knowledge of how to reduce or mask smoke character, however, there
are no known processes to completely remove all smoke compounds from a wine.
1. GENERAL RECOMMENDATIONS
- Take notes on the duration of the smoke exposure in the vineyard and the proximity of the fire. Fresh smoke can cause more damage compared to smoke that has traveled significant distance.
- Smoke analysis on berry samples can give an indication of the potential level of smoke taint, but small batch fermentations are a better way to estimate the level of damage in the vineyard. The UC Davis link below has a detailed protocol on small lot fermentations specifically for assessing smoke damage to grapes.
- Wash ash off fruit in the vineyard before harvest when possible.
- Hand harvest is preferred over machine harvest. If machine harvest is the only option, separate the first juice that comes out of the harvest bins or out of the press when making white or rose.
- Remove all MOG from fruit during processing. Leaves contain a significant amount of smoke compounds that can be released into the juice during maceration.
- Using oak during fermentation and aging can increase guaiacol levels in the wine. If smoke exposure analysis numbers will be used for insurance or contract issues, avoid using oak.
Analysis and testing for smoke impact during harvest can be difficult for a number of reasons : different analytical methods, different fires resulting in different types of impact, and different threshold levels of the compounds related to smoke on the various varietals used in winemaking. There is a great amount of complexity in this ongoing field of research.
Therefore, we present current content published by four of the major research institutions and analytical services in the wine industry from across the globe. Please see the following sensory threshold and impact guidelines from The Australian Wine Research Institute, ETS Laboratories, Washington State University and Washington Winegrowers, and UC Davis.
- Australian Wine Research Institute (AWRI) – Sensory Impact of Smoke Exposure
This short fact sheet covers sensory thresholds of the common volatile phenolic smoke compounds and the sensory impact of glycosides with links to many more smoke taint resources.
- ETS Laboratories – Smoke Impact in Grapes and Wine
ETS provides an explanation of the testing available and further links for interpreting results and current recommendations.
- Washington Winegrowers- Smoke Exposure Resource Site
A great resource for up-to-date information on working with fruit exposed to wildfire smoke. There are links to webinars, smoke analysis laboratories, micro ferment instructions, and how to talk about smoke with winery customers.
- UC Davis – Wildfire and Smoke Exposure Resources
Helpful website outlining grape sampling protocols, micro fermentations for assessing potential smoke damage in fruit, and a list of
frequently asked questions and answers on smoke exposure.