As global temperatures and atmospheric carbon dioxide rise due to climate change, the incidences of wildfires will increase with the passing years. Which is problematic for winemakers since, it is well known that when vineyards are exposed to smoke they accumulate volatile phenols leading to undesirable sensory attributes. Commonly, wines exhibiting ‘smoke taint’ are described as having smoky, ashy, dirty, burnt, and medicinal characteristics. Analysis of wine from grapes subjected to smoke show a significant increase in volatile phenols such as guaiacol, 4-methylguaiacol, 4-ethylguaiacol, and 4-ethylphenol. Guaiacol and 4-methylguaiacol are routinely analysed in their free form as indicators of smoke taint.
However, analysis of these molecules by their free form alone is not the best indicator, as these molecules bind to glucose in the grapes producing glycol-conjugates. There is no correlation between the amount of free smoke taint associated volatile phenols and their glycol-conjugate counterparts. In many cases low concentration of the free form were found in wines or juice made from smoke tainted berries and high concentrations of their conjugates were measured. These compounds must be hydrolyzed from their glucose counterparts in order to produce the negative sensory aspects that are observed in wine subjected to smoke. Acid hydrolysis has been shown to release these volatile phenols; as well as, enzymes present in human saliva which are capable of hydrolyzing glycol-conjugated phenols to their volatile forms in the mouth during tasting. Low levels of smoke taint associated volatile phenols does not allow for the accurate assessment of smoke taint due to formation of glycol-conjugates; thus, analysis of volatile phenols by acid hydrolysis must be done to ensure the quality of a finished wine.
Analysis of berries and juice or wine from berries exposed to smoke is crucial due to the low odor threshold of the smoke taint volatile phenols. HS-SPME GC-MS/MS is the most effective way to isolate volatile phenols while providing optimum sensitivity enabling these molecules to be detected at low concentrations.