Grapes that are exposed to smoke from wildfires often contain what is referred to as “smoke taint”: highly undesirable smoky, ashy, or medicinal characteristics that drive quality as well as price down. This is a phenomenon known all too well in many regions around the world.

Research has found links to several compounds in wine to the presence of smoke taint, including guaiacol, 4-methylguaiacol, syringol, 4-methylsyringol, p-cresol, m-cresol, and o-cersol. More recent research has further discovered that it is the glycoconjugate forms of these compounds that when metabolized during fermentation release volatile compounds that give off the trademark smoke taint flavor and aromatic characteristics in contaminated wines.

In terms of the degree of smoke taint present in wines, the timing of the smoke exposure plays a major role, while at the same time so does winemaking techniques, the type of yeasts used, and the use of oak barrels also play a significant role in the amount of smoke taint present in the contaminated wine.

Whilst we understand a fair amount about smoke taint in wines this remains an important area of research as there is still a lot to learn. For example, while it is very well understood how grape maturity affects the aroma, flavor, and overall quality of a wine, it is not known how grape maturity affects smoke taint aromas and flavors in contaminated wines (if it even does).

Therefore, a new study published in the journal Molecules aimed to add to the growing knowledge of smoke taint in wines by examining the effect of grape maturity on smoke taint in wines.

Brief methods

This was a controlled study in an experimental vineyard at the University of Adelaide, Waite Campus, in Adelaide, South Australia.

Chardonnay, Sauvignon Blanc, Merlot, and Shiraz grapevines were placed in either one of two treatments: smoke or control (no smoke). Vines undergoing the smoke treatment were surrounded by “smoke tents” built for the study, and were exposed to one hour of smoke 7 days after veraison (the start of ripening).

Grapes were harvested at two different time points: the first at a ripeness level appropriate for making sparkling wines or light-bodied wines (TSS 16-20oBrix), and the second at a ripeness level appropriate for full-bodied wines (TSS 22-25oBrix).

Wines were made from these grapes without undergoing malolactic fermentation. For each variety, two wines were made: 1) smoked and 2) control.

The following chemical analyses were made on all wines: pH, titratable acidity, volatile acidity, ethanol content, wine color density, hue, total phenolics, volatile phenols, guaiacol, 4-methylguaiacol, syringol, 4-methylsyringol, and total cresols.

A descriptive sensory analysis was performed by a panel made up of staff and students (10 female, 3 male) from the University of Adelaide and the Australian Wine Research Institute who all (except one) had experience with descriptive analyses of smoke tainted wines.

Training sessions were performed to make sure everyone was on the “same page” with the analysis, with the actual experimental sessions occurring in isolated booths. Panelists sampled and evaluated three replicates for each wine/smoke treatment …

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