As global temperatures and atmospheric carbon dioxide levels rise, the incidences of wildfires will increase. This is problematic for winemakers, since 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 exposed 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 of a potential sensory fault, as these molecules bind to glucose in the grapes, producing glycoconjugates. There is no correlation between the amount of free smoke taint associated volatile phenols and their conjugated counterparts. In many cases low concentrations of the free forms were found in wines or juice made from smoke tainted berries, and high concentrations of their conjugates were measured. These compounds must be released from their conjugated forms 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. Low levels of smoke taint-associated free volatile phenols do not allow for the accurate assessment of smoke taint on their own; analysis of volatile phenols after acid hydrolysis must be done in parallel 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. GC-MS/MS is the most effective way to detect these molecules at the very low concentrations that can result in sensory faults.