Volatile phenols: smoke, spice and sticking plaster

Grouping these together is unusual, and it earns its place: understanding that the smoky note in an oaked wine, the medicinal note of a Brett-affected one and the ashtray note of a smoke-tainted one belong to the same chemical family explains a great deal of otherwise confusing tasting vocabulary.

Oak toasting thermally degrades lignin in the wood, producing guaiacol and related compounds associated with smoke, spice and toast. These are extracted into wine during barrel contact and are a normal, intended part of oaked wine.

Brettanomyces converts hydroxycinnamic acids naturally present in grapes into 4-ethylphenol and 4-ethylguaiacol, associated with sticking plaster, farmyard and clove characters. Published thresholds for these vary widely with the wine matrix.

Wildfire smoke contains the same guaiacol and cresol family. Grapes absorb them through the skin, and the vine binds much of the load into glycosides — sugar-bound forms that are not volatile and therefore not detectable by smelling the fruit.

Those bound forms are the central difficulty with smoke taint. They can be released during fermentation and, more slowly, in bottle, so a wine can taste clean at pressing and show ashy character months later.

The three routes are distinguishable analytically, which matters commercially, but the sensory overlap is real.