NYT: Sulfur

Here's something I read from a NYT article I thought was interesting. Enjoy!
August 5, 2008

A trick using a copper penny can work for all sorts of sulfur-related ills. (Photo: David Zalubowski/Associated Press)

Sulfur
By Eric Asimov
My column in Wednesday’s newspaper is on some mouthwatering white wines from Greece, and in the course of our wine panel tasting I ran into a vexing problem that has taken me deeply and perplexingly into the realm of wine and sulfur chemistry.
It began simply enough. As often happens, particularly when tasting a large number of white wines, especially those that are fermented and aged in steel tanks, I detected in several of the wines the aroma of burned matches.
If I could offer a hyperlink to this aroma you would recognize it right away – that flinty smell after you strike a match and blow it out immediately.
Often, but erroneously, that aroma is attributed to an excess of sulfur dioxide in the wine. Sulfur dioxide has for eons played an important role in both preventing the effects of oxidation and inhibiting microbial growth in wine. Judging by the scientific treatises I’ve buried myself in, that’s probably a gross oversimplification of the role of sulfur dioxide. Suffice it to say that, while a few great wines are made without the addition of sulfur dioxide, the chemical is almost universally used throughout the wine world. But, while the matchstick smell is related to sulfur, sulfur dioxide is not the guilty party.
The issue came up because one of the wines we rejected due to the matchstick smell turned out to be the one Greek white that I have regularly enjoyed at home. In fact, I’ve mentioned it twice in posts, once in the spring, and once last summer. It’s the Thalassitis from Gaia, a white made from assyrtiko grapes grown on the island of Santorini.
I’ve really enjoyed this wine. It’s got a floral and mineral character, with the faintest suggestion of honey, and it’s not only refreshing but interesting. I wondered why in the blind tasting I was turned off by it. One difference was significant – my two posts were about the 2006 Thalassitis, while the bottle in our tasting was the 2007.
I knew I had a bottle of the 2007 at home, so one night shortly after the tasting I opened it. Again, the smell of struck matches. At the panel tasting, the smell had not dissipated after an hour of swirling and sniffing, so I decided to decant the wine. Often the smell disappears with exposure to air. But even after decanting and leaving the wine for 10 or 15 minutes, it was still there.
Now, let’s be clear – the aroma is certainly not harmful. It’s simply off-putting. To understand why it occurs I checked in with Prof. Roger B. Boulton at the School of Viticulture and Enology at the University of California at Davis. Dr. Boulton explained that matchstick aromas are caused by thiols, sulfur compounds that can result from the yeast fermentation.
When these aromas develop, he said, many winemakers try to solve it by aerating the wine after fermentation is complete. Instead, the aeration converts the thiols into disulfides, compounds that are heavier than thiols and more difficult to eliminate. In effect, the aeration simply buries the aroma in the wine.
“You’ve converted something that was very volatile into something not so volatile,’’ Dr. Boulton told me. “You think you’ve gotten rid of it, but you haven’t gotten rid of it at all.’’
Strangely, the aroma thereafter surfaces periodically but unpredictably. Exposing the wine to air — by decanting, for example – can suppress the aroma enough to make the wine enjoyable, but it doesn’t eliminate it. Even with the aroma, the wine is palatable — some people aren’t bothered by it at all.
“Once it’s in the disulfide form, you can’t treat it,’’ Dr. Boulton said. “The irony is that if a wine is aerated to get rid of it, it just makes it more difficult to get rid of.’’
While winemakers do not want the thiols to convert into disulfides, also known as mercaptans, it’s beyond this post to explore what can be done about it. Dr. Boulton suggests that winemakers treat the wine immediately with copper sulfate. Of course, that’s after the fact. A fermentation that does not produce thiols is the best solution – but apparently that’s easier said than done. For a more in-depth look at the chemistry issues, Jamie Goode, whose excellent wineanorak.com contains a wealth of information of all kinds, has written this essay.
So what can the consumer do? Dr. Boulton says copper or silver can both help to eliminate the off aromas. The copper penny trick works for all sorts of sulfur-related ills, from the matchstick aroma to the rotten egg aroma, which is a completely different problem. You simply find a clean copper penny, which is not so easy anymore. Since 1982 (according to wikipedia.com) the American penny is 97.5 percent zinc, with a thin copper plating. Previously, the penny had been 95 percent copper. Simply swirl the penny, even the newer penny, in the wine and the sulfur effect should dissipate.
Alternatively, you could carry a silver spoon around and use it to stir the offending wine.
“If somebody sees you they might think you’re weird,’’ Dr. Boulton said, “but it will clear it up.’’