Identification of Smoke Odorants by Gas Chromatography/Olfactometry and Assessment of Smoke Odorants in Grapes and Wine
The long-term goal of this research is to investigate the complex conversion mechanisms of smoke compounds and develop a quantitative measurement to ensure grape and wine quality.
Specific objectives are to:
- Identify and confirm the compounds that have a “smoky” aroma character by gas chromatography-olfactometry.
- Develop reliable analytical protocols for analyzing smoke odorants in different wines.
- Build a quantitative database for the smoke odorants in non-smoke affected wines and use the database to assess smoke-tainted wine.
- Investigate the smoke odorant precursors in grapes and study how these precursors convert to smoke odorants during enology and the aging process.
Importance to the Oregon wine community:
With global warming and climate change, smoke taint has become a significant concern for the U.S. wine industry, particularly in Southern Oregon and California. Smoke taint is an off-aroma describing wine with smoky, medicinal, and ashy characters, and this unpleasant taint is caused by grapes or grapevines exposed to bushfire smoke before grape harvest.
It has been reported that during fires, smoke compounds can permeate the grape skins and bind with sugar molecules to form nonvolatile compounds. The bounded compounds can be broken down during the fermentation and aging processes, releasing undesirable aromas in wine. Although a large amount of research has been published on the volatile compounds that might be associated with smoke taint, such as volatile phenols, the actual root causes of smoke taint in wine have not been fully understood. This research will lead to the identification of the exact smoke compounds in wine, so their absorption and conversion by grapevines can be further investigated.
Progress so far:
Two smoked red wines resulting from the 2015 fires were donated from E&J Gallo Winery. Six cases of 2018 rosé wine made from Pinot noir grapes from Southern Oregon were included. In-house informal sensory evaluation showed that the smoked red wines have distinct smoky, ashy notes.
Two sensitive and reliable analytical methods were developed based on solid-phase microextraction-gas chromatography-mass spectrometry (GC-MS) and stir bar sorptive extraction–GC-MS with isotope dilution analysis. Both smoked wines and normal wines were analyzed, and the results showed that the concentrations of some suspected smoky volatile phenols (4-methylguaiacol, 4-ethylguaiacol, and 4-ethylphenol) were similar in the smoked wines and the normal wines, suggesting they were not the culprit for smoked wines.
Although the concentrations of a few other phenolic compounds were higher in the smoked wines than that of the normal wine, their levels are below sensory detection thresholds. The data suggested that synergistic effects and aroma interaction could cause smoky aroma, or some other compounds might be involved in the smoke taint.
Ongoing research is working to isolate the smoke compounds from wine and analyze them using gas chromatography/olfactometry-mass spectrometry, e.g., using an instrument and human nose to sniff out the smoke-contributing compounds.