Dr. Michael C. Qian, of the Department of Food Science and Technology, Oregon State University and Oregon Wine Research Institute, has prepared the update below. This project receives funding from the Oregon Wine Board as part of its viticulture and enology research grant program.
One of the increased concerns of the Oregon wine industry is related to vine stress. Although the off-flavor descriptors vary from winery to winery, frequent descriptors used in the wineries include “tequila,” “shellfish,” “peanut,” “ashtray,” “dry weed,” “herbaceous,” “flint” and others. In young wine, the taint smells like “bay leaf,” and the wines do not age well. There were observations from wineries that taint could be related to compromised or nutritionally imbalanced fruits from stressed vines, induced by drought, nitrogen deficit or a combination of many factors, but the exact cause(s) have never been studied or documented. This research is aimed at identifying the chemical nature of these off-flavors.
Off-flavored wines were obtained from industry collaborators from the Willamette Valley. The stressed vine off-flavor was characterized by a sensory panel consisting of winemakers familiar with stressed vine off-flavor and OSU researchers. The panel was able to characterize the stressed vine off-flavor from the wines collected from the industry. After the initial wine collection and sensory evaluations, more wineries have been contacted and more stressed wines have been collected from the industry.
Non-targeted volatile analysis was performed on the eight off-flavor wines obtained from the industry. Twenty normal Pinot noir wines were also analyzed for comparison. Volatiles including higher alcohols, esters, volatile phenols and TDN (kerosene aroma) were analyzed by solid phase micro-extraction-GC-MS and stir bar sorptive extraction-GC-MS. The result showed that the off-flavor and normal wine had different concentrations of many compounds, and TDN, 4-vinylphenol, 4-vinylguaiacol, 3-ethylphenol, ethyl propionate, ethyl 2-methylpropanoate and 2-methylpropanoic acid can be used to distinguish the off-flavor and normal wines; however, the exact chemical nature of off-flavor is still a mystery.
Work in progress is using GC-olfactometry technique to identify the off-flavor compounds. Volatiles have been isolated from the off-flavored wines, and initial GC-O experiments have been performed. However, due to the complexity of wine aroma in general, it is not obvious to pinpoint the compound(s) responsible for the off-flavor. This is normal and expected; more thorough aroma fractionation and GC-O is in progress to identify the compound(s).
Other OSU and OWRI researchers involved in this project:
Xiaoyu Wang, visiting faculty; Yanping L. Qian, assistant professor & research scientist; Elizabeth Tomasino, assistant professor, Department of Food Science and Technology