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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Research Project #438756

Research Project: Measuring Grape Smoke Exposure Impact

Location: Crops Pathology and Genetics Research

Project Number: 2032-21220-008-033-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Aug 1, 2020
End Date: Jul 31, 2024

Objective:
Smoke taint has become a recurring issue since 2008, and one that has led to crop losses as well as legal disputes between growers and processors. With the expectation that fires will become a part of the California summer ecology, it is important to have some means to determine risk and mitigate the taint from smoke exposed grapes. Many basic questions remain such as how quickly volatile phenols (VP) absorb into grape skins, including varietal differences. Anecdotal evidence suggests differences in sensitivity among different grape varieties; this has not been specifically investigated or quantified. Studies investigating the potential of barrier sprays on grapes to absorb VP are ongoing with variable results. Another question is whether ash is a potential carrier of VP and should it thus be washed from the grapes before processing or not? Does freshness of the ash play a role? Can we develop an easy means to measure potential smoke exposure and smoke taint risk in the vineyard? What are the optimal grape sampling and processing methods that will relate the best to smoke exposure markers in the final wines? We developed a simple contained atmospheric system. This same system will be used to investigate the objectives below. 1. Investigate kinetics of VP absorption into grapes berries and leaves and potential translocation from leaves to grape berries. 2. Investigate ways to determine smoke exposure risk assessment in the vineyard and potential mitigation by grape sprays. 3. Determine the impact of wildfire ash on VP absorption into grape berries and resulting wines.

Approach:
We developed a contained atmospheric system (CAS) which will be customized to expose grape bunches and leaves separately to known concentrations of VP at different times during development to determine change in absorption depending on ripeness, potential differences in absorption between different varieties as well as translocation of VP (free and bound) from leaves to grapes. Determining methods to measure VP’s in the air and relating it to grape absorption levels are potential ways to monitor smoke exposure risk in vineyards. Grapes will be exposed to ash produced from the burning of local vegetation (Quercus lobate and manzanita) over time and VP absorption monitored. Small scale winemaking with the inclusion of ash will be undertaken and the VP composition will be compared with controls fermented without the presence of ash. The recommended grape processing method by the Australian Wine Research Institute of small-scale fermentations (5-day process) will be tested for potential optimization with a reduction in time to a maximum of 3 days.