If That Sauvignon Blanc Smells Skunky, Here’s Why

Sauvignon Blanc’s classic aroma lends itself to multiple descriptors, from asparagus to boxwood to urine-stained kitty litter. Organically, Thiols (also known as mercaptans) are the source of the aromas. Thiols are also the source of what makes a skunk’s spray smell the way it does. 

Loosely, mercaptans/thiols are sulfur-containing compounds which replace oxygen; they come in a few levels of concentration that produce their own aroma profile. One concentration of the compound in wine can create what is known as “reduction.” Some reductive aromas in oxygen-starved wine are contained enough to be desirable; some are not. Many aromatic white grape varieties manufacture these sulfurous compounds in the vineyard, but Sauvignon Blanc is particularly known for its powerful natural production of thiols. This subject was featured recently in Wine Business Monthly’s Winemaker Trial section and covered by writer Stacy Briscoe. Briscoe had discovered a trial going on at Chemeketa Community College, located in Oregon’s Willamette Valley.

Interest in Sauvignon Blanc has been growing in Oregon, but the variety remains relatively uncommon in the state’s wine industry. According to Briscoe, that uncommonness led Scott Dwyer, wine studies instructor at the college to engage his students in a study of Sauvignon Blanc in the vineyard, specifically to weigh a possible connection between timing leaf pulling from vines during the early growing season to affect thiol development.

Leaf pulling is a standard practice to help control the grape crop by providing exposure to sun, reducing moisture exposure, opening up areas for fungicide and pesticide sprays to penetrate better and give the crop a better chance at becoming flavor-concentrated wine. Generally, a first leaf pulling is recommended between two and four weeks of fruit set. Dwyer’s students set out to see what the effect of heavy early leaf pulling would have on Sauvignon Blanc’s thiol concentration. They hand-pulled leaves immediately after the fruit set on two of four sample vineyard rows. At harvest time, grapes picked from the rows that had been leaf pulled early were separated from grapes picked from rows that had been handled as usual (the control). The two lots were kept separated but handled identically through fermentation, storage and finishing.

Dwyer told Briscoe the separate lots were sensorially different throughout fermentation, but as time progressed through process and storage the wines grew more and more similar. In the end, the test wine as well as the control wine proved thiol-rich and aromatic. The overall preference among Dwyer and his students during the fermentation was for the test wines, which presented grapefruit passion fruit aromas as opposed to the control wines, which smelled more like boxwood. After fermentation, the aromas seemed to meld between the test and control wines. But Dwyer said that in a blind tasting of the finished wines, ‘…a significant majority of participants identified the control as having higher concentrations of thiols, which was later confirmed through analysis.’ 

He also said that his group’s results contradicted previous studies that showed heavy leaf pull at fruit set results in increased thiol concentration. Dwyer concluded that thiols were higher in the control, which had not undergone early leaf pull, and the aromas leaned toward the reductive side, which, he said, was not the goal of the study. In his opinion, the reductive thiols are not the “right ones.” Many wine consumers and professionals agree with Dwyer about right and wrong thiols–from my second paragraph: “some reductive aromas in wine are contained enough to be desirable; some are not.”

Dwyer plans to do the same test across different growing seasons; the aim is to find out whether trials could identify the kind of growing season necessary for more or for less thiol development—or maybe future trials could identify specific processing techniques to control thiols for a desired trait. 

My desire is for less reductive thiols, what’s yours?