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How to Assess Whether Grapes & Wines are Affected by Wildfire Smoke Exposure

Oregon State University Extension — Vineyards on the west coast have experienced wildfires over the past few years and are currently faced with a difficult 2020 wildfire season. Vineyard exposure to smoke can lead to smoky aromas in wines. While grapes can be tested for smoke marker compounds, wines produced from micro-fermentations can yield more comprehensive information when they undergo sensory and analysis for both free and bound volatile phenols that may impact wine sensory properties. Micro-ferments are small fermentations that can be done by grape growers or winemakers as a way to evaluate smoke-derived compounds in the grapes. See the procedures for conducting micro fermentations.

Collecting grape clusters from throughout a smoke-exposed vineyard will serve as a sample for smoke compound testing and/or micro ferments to determine if the fruit and/or wine carry the volatile phenols from the smoke — Josh Price

How to analyze for smoke-derived compounds

Currently there are few labs that provide grape and wine testing for smoke compounds. Due to the large number of samples that have been submitted to testing labs under the present wildfires, there is limited availability of timely service. If your vineyards have been exposed to wildfire smoke, it is recommended that you prioritize vineyard lots to sample for analysis. The most common reasons to pursue analytical testing is 1) requirement for crop insurance claims, and 2) contract negotiations with grape buyers. See “Further considerations” below. When sampling, identify vineyards that you suspect were more heavily affected by smoke exposure and collect clusters from throughout these blocks to provide a single sample that represents the area. Sampling and sample preparation protocols vary between testing laboratories, so be sure to check their specific requirements before sampling and preparing samples for shipping. Consider collaborating with neighboring vineyards in your area to collect samples from vineyards that represent the area, especially if you are under similar smoke exposure. Separate your samples based on variety, as different varieties have shown different results with the same smoke exposure intensity or duration. Reducing the number of samples to be analyzed will help you reduce the total cost of analysis across producers and provide a regional outlook of smoke impact. A list of testing labs is below (in alphabetical order). Be sure to contact the lab to determine how to collect and submit your sample. Be aware that turn-around time for sample analysis will vary, so make sure you know how long it will take to receive results and plan accordingly.

Additional documentation may be required for shipping to Canada. Contact Davin Potts (davin.c.potts@usda.gov), 509-925-1189 for additional guidance
 
Evaluating wines from micro fermentations

Sensory evaluation of wines from micro fermentations may provide you with timely and actionable information. However, they must be conducted in a careful and consistent manner. How to conduct sensory evaluation of micro fermentations is outlined within the protocol for micro fermentations

and includes the following:

  • Having multiple people (4 people minimum if possible) taste the samples. People vary in their sensitivity to the sensory impact of the smoke compounds.
  • Taste sample at least twice during a short period of time.
  • Ensure breaks of 2+ minutes between samples to reduce any carry-over effect.
  • Samples should be tasted blind, meaning coded samples with no identifiers.
  • Be aware that freshly fermented wines from a micro fermentation may taste a little bit different than what you are used to in normal production. The wines may be more acidic, astringent, and have higher amounts of solids. Focus on identifying smoky characteristics. A helpful tool is to have a heavily smoke impacted wine as a reference as well as a wine that has no smoky characteristics. Wines from previous micro fermentations that do or do not exhibit significant smoke impact could be used as a reference when tasting.

Further considerations

  • If you have crop insurance, be sure to contact your insurance company and talk to your crop insurance adjuster before you begin sampling and/or harvesting. They will work with you to identify the proper steps in pursuing your claim.
  • If you are selling/buying fruit, be sure to work with your grower/buyer/winery to consider micro fermentations and what threshold of smoke exposure or analytical metrics will be acceptable.

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