Smoke Taint in Wine

A few weeks ago, my husband pointed me to an article written by one of our friends in California, Professor Phillip Crews who is a chemist at UC Santa Cruz and is also a winemaker at Pelican Ranch Winery. Phil became interested in smoke tainted grapes after the Mendicino Complex Fire in 2018. The results of his research appeared in the Journal of Natural Products in March 2022.
The insidious nature of smoke taint is that it is odorless in wine until transformed by saliva into flavors that are described as "ashy", "bitter" or "smokey". While the authors focussed their research on Cabernet Sauvignon, they examined other varietals including Merlot, Cabernet Franc, Malbec, Pinot noir, Syrah, Grenache, and Zinfandel.
During a wildfire, volatile phenols in smoke can rapidly diffuse through the waxy grape cuticle and become transformed and bound into phenolic diglycosides (PD) by the action of uridine-diphosphate glycosyltransferases (UGDTs).¹

There are more than 500 volatile phenols that are contained in wood-derived smoke, of those 500, approximately 34 volatile phenolic compounds have been identified from wildfire smoke or barrel toasting or released by grapevine leaves.
Volatile phenols are mainly translocated through the waxy cuticle of the grape berry and then converted into bound phenolic diglycosides (PD). There are 6 classically bound PD chemical markers. In-mouth breakdown of PDs occurs by enzymes or bacteria present in human saliva, which cleave the glycosidic bond and releases the offensive-smelling phenols.
The authors then selected these six phenolic diglycoside (PD) marker compounds phenol rutinoside, 4-creosol rutinoside, guaiacol rutinoside, 4-methylguaiacol rutinoside, sryingol gentiobioside, and 4-methyl sryingol gentiobioside. If the sum of the 6 compounds was less than 6 ppb, the wine was deamed to be fine, it the sum of the 6 compounds was greater than 30-820 ppb the wine was flawed with smoke taint.

Understanding the first steps in translating smoke in vineyards to ruining finished wines is still evolving but include proximity of a vineyard to wildfire(s), fuel source, smoke exposure duration (>1 h or more), age of the smoke, wind patterns, land topography, and heat inversions.
References:
1.Phillip Crews*, Paul Dorenbach, Gabriella Amberchan, Ryan F. Keiffer, Itzel Lizama-Chamu, Travis C. Ruthenburg, Erin P. McCauley, and Glenn McGourty, Natural Product Phenolic Diglycosides Created from Wildfires, Defining Their Impact on California and Oregon Grapes and Wines, J. Nat. Prod., 2022, 85, 3, 547–561, March 3, 2022.