Research Project: Assessment of Smoke Exposure Impacts on Grape and Wine Quality and Techniques for Mitigation in the Vineyard and in the Winery

Location: Horticultural Crops Production and Genetic Improvement Research Unit

Project Number: 2072-30500-002-011-A
Project Type: Cooperative Agreement

Start Date: Apr 1, 2026
End Date: Mar 31, 2030

Objective:
This Agreement will continue ongoing work from the current NACA agreement #58-2072-4-026, entitled: “Assessment of Risk to Grape and Wine Quality from Smoke Exposure and Evaluation of Methods for Mitigation of Smoke Exposure in the Vineyard and in the Winery”, modifying existing objectives and adding others to reflect the current state of the work. Specific objectives for the new agreement will include: 1. Continuation of the previous objective to evaluate the use of nanofiltration coupled with immobilized glycosidase enzymes for the reduction of both free and glycoside enzymes forms of smoke related volatile phenols. This objective has been expanded to include the evaluation of additional glycosidase enzyme preparations (the original objective focused just on B-glycosidase from almonds) as well as the use of molecularly imprinted polymers (MIPS) or other adsorptive media for the removal of volatile phenols released by the immobilized enzymes. 2. Continuation of the previous objective to use the system previously developed for conducting exposures of field planted grapevines to smoke from various fuel sources. Fruit and leaf samples created under this objective will support the redox trials in Objective 3, as well as ongoing collaborations with other USDA and WSU researchers. As before, this objective will focus on both fuel sources and timing of smoke exposures relative to grape berry development to provide both pre- and post-veraison samples for these collaborations. 3. The third year of an objective focused on evaluation of the role that redox status during fermentation plays on the expression of smoke related volatile compounds in the resulting wines, including the formation of sulfur-containing metabolites of volatile phenols (thiophenols) as the compounds are expected to be sensitive to the redox conditions during the fermentation. 4. Evaluation of methods for the removal of kaolin and/or bentonite barrier sprays applied to grapevines prior to smoke exposure as a means of reducing the uptake of smoke related compounds during an exposure. Previous work has demonstrated that the barrier sprays must be removed after the smoke exposure has ended to have the best impact on the reduction on the concentration of guaiacol and other smoke marker compounds in the fruit and in the resulting wines. This objective will optimize the process for removing the barrier spray materials post-exposure.

Approach:
Objective 1 is the ongoing project of a graduate student who has used immobilized B-glycosidase from almonds to do preliminary treatment of smoke-affected wines and permeates from affected wines. Next steps will include assessing the efficacy of other purified glycosidases as well as commercially available preparations of glycosidase enzymes which may include other enzyme activities as well. These trials will evaluate the extent to which using glycosidase enzymes with broader activities will result in more complete hydrolysis of the glycoside pool in smoke affected wines. She has also started the development of an activity assay based on hydrolysis of individual glycosides of volatile phenols known to be present in smoke-affected grapes and wines, as an alternative to the started assay for glycosidase activity based on the glucoside of p-nitrophenol. The standard assay has not been useful for the prediction of glycosidase activity for the specific glycosides that are the focus of this project. This objective will also evaluate the use of molecularly imprinted polymers (MIPS) and other adsorptive resins for the removal of the volatile phenols released by the glycosidase activities. These products offer the promise of better selectivity than carbon for volatile phenols, resulting in less collateral damage to desirable aroma compounds during treatment. Objective 2 Researchers will use a previously developed field-based system for the controlled exposure of vines to smoke. The system includes 6 modular hoophouses, each of which covers 30 vines, 3 houses are used for smoke houses, and 3 houses are used as controls. Smoke is generated in side-firebox smokers, using either collected fresh or dried plant materials, or using pelletized plant materials, most recently a variety of rangeland plants collected in the Columbia Basin near Tri-Cities. Smoke density is monitored using particle counters, while smoke composition will be monitored using Tenax sorbent tubes and whole air sampling with canisters. Exposures are typically 36 hours in duration, with 4-5 conducted each season, depending on weather and the presence of actual wildfire smoke events during the season. Leaf and cluster samples are collected at regular intervals during the smoke exposure for later analysis at the WSU Wine Science Center. Objective 3 will focus on monitoring and/or controlling the redox level during fermentation to evaluate the relationship between redox level and the development of thiophenols and other smoke related compounds during fermentation. The formation of sulfur containing volatile compounds is expected to be sensitive to redox level. In this study, the impact of varying the minimum redox state during fermentation on the composition of smoke-related phenols and thiophenols in the resulting wines. Preliminary trials were conducted during 2025 to develop the protocols that will be used during 2026. Objective 4 will focus on optimization of the removal of kaolin barrier spray materials at the conclusion of a smoke exposure trial. This trial will focus on the use of various sprayer types, as well as water versus water with various adjuvants added.