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Many people like a certain flavor of smokiness in food and alcoholic beverages, and certain types of wines aged in toasted oak barrels are appreciated for their smoky notes. However, the sensation is totally different for wines produced with grapes contaminated by smoky air from nearby fires. Wines from smoke-exposed berries are characterized by an unpredictable ashy flavor and taste, greatly impacting the quality and market value of the final product. Brand loyalty is built on consistency, so many winemakers are wary of risking their reputation on smoke-tainted grapes.

The wine industry has a strong financial impact, generating more than $50 billion US dollars in the United States alone [Ref]. Therefore, many efforts are spent attempting to mitigate smoke taint effects, especially on highly prized wines, through studies on how to detect and prevent them.

In my previous blog, I discussed Headspace Solid Phase Micro Extraction (HS-SPME) combined with GC-MS as a powerful tool for the determination of low levels of volatile organic compounds from complex matrices, making this solution a key analytical technique for chemists involved in wine aroma characterization.

At that time, I anticipated a collaboration between our Application Team in Runcorn, UK, and an important wine producer in the US, Jackson Family Wines of Santa Rosa, California. This collaboration allowed the optimization of a rapid and sensitive analytical method for the quantitation of smoke taint compounds by HS-SPME combined with triple quadrupole GC-MS/MS.

Like many other wine producers, Jackson Family Wines is facing a growing threat due to more frequent wildfires in the areas of grape cultivation. When it happens in the growing season, grapes are exposed to smoke.

The analytical characterization of volatile components, especially the ones having a high sensory impact, is key for improving wine quality and consequently its value on the market. Through correlation studies between chemical and sensorial analyses, it is possible to identify off-flavor markers, maturity markers, aging bouquet markers, as well as markers for exogenous contamination.

Volatile phenols (VPs) such as guaiacol, syringol and 4-ethylphenol, are the compounds associated with smoke taint characteristics for grapes and wines and can be found in free and glycosylated form — the non-volatile precursors responsible to release the free form during the fermentation process. Understanding the concentration of free and bound volatile phenols in wine and in smoke-exposed berries before fermentation is of critical importance for wine producers. They must acquire knowledge on the potential for perceptible smoke taint in the resulting wine, and possibly minimize a financial loss on the production.

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A rapid and sensitive determination of free and conjugated VPs as smoke taint markers is therefore required. The tested method involves acid hydrolysis of the sample prior to the extraction, in order to release the bounded compounds in their free form for GC analysis. Then, fully automated sample extraction and pre-concentration of VPs is achieved with the Thermo Scientific™ TriPlus™ RSH autosampler configured for SPME, while the required selectivity and sensitivity are obtained with the Thermo Scientific™ TSQ™ 9000 Triple Quadrupole GC-MS/MS.

SPME headspace sampling reduces the complexity of the matrix with minimal sample preparation while the selectivity of SRM acquisition helps to discriminate between the target compounds and the matrix interferences. The reported chromatograms show an example of a full-scan (m/z 50–500) total ion chromatogram (TIC), and the MS/MS signals of the target compounds from a wine sample spiked at 5 μg/L.

This method allows the separation of the target compounds in less than 12 min. The automated workflow and the short cycle time support large testing laboratories to face high workload demand during the harvest months.

To know more about the method, don’t miss the Application Note AN10752 developed in collaboration with Jackson Family Wines.

A) Total Ion Chromatogram (TIC) (m/z 50-500); (B) SRM acquisition of target VPs.

A) Total Ion Chromatogram (TIC) (m/z 50-500); (B) SRM acquisition of target VPs.

This method allows the separation of the target compounds in less than 12 min. The automated workflow and the short cycle time support large testing laboratories to face high workload demand during the harvest months.

To know more about the method, don’t miss the Application Note AN10752 developed in collaboration with Jackson Family Wines.