Unintended Bottle Bouquet the Flipside of TCA

In an earlier post, I wrote about how using cork closures, as well as using chlorinated products for sanitation can lead to a wine illness called cork taint. Well, all is not safe merely by switching over to screwcaps because screwcapped wines can be stinky in another chemical way.
George Taber wrote in his book To Cork or Not To Cork, about Alan Limmer, chemist and winemaker who had concerns about high-tannin wines like Syrah and Cabernet Sauvignon under screwcaps. Alan Limmer wrote an article for the New Zealand Winegrower entitled The Chemistry of Post-bottling Sulfides in Wine where he makes an argument that there is a difference in redox (reduction-oxidation) chemistry in wine under cork versus screwcap closures. Limmer goes on to say that wine can never be bottled free of sulfides. The more noticeable sulfides are the simple sulfides such as H₂S or hydrogen sulfide which smells like rotten eggs and H₃CSH or methanethiol (methylmercaptan) which smells like rotten cabbage or burnt rubber.¹ Delightful! not!
Traditionally, wineries rack their wines to get rid of the simple sulfides such as hydrogen sulfide. Methanethiol, on the other hand may simply be oxidized to dimethyl disulfide which has a much higher sensory threshold. Therefore, if there are disulfides in the bottled wine, and the wine is under a sufficient reducing environment such as a screwcap, the following equilibrium can occur where the dimethyl disulfide is reduced back to methanethiol which has a much lower sensory threshold.

Once this chemical explanation of redox in bottled wine was discovered, screwcap manufacturers such as Stelvin have found a way increase oxygen permeability. Saran/tin and Saranex are used by all screwcap manufacturers, of which there are now several. Saran/tin has a metal layer, which allows very little oxygen transmission, Saranex allows a bit more in order to keep the redox environment from sifting back to a reducing environment.²
Many articles have been written on the proper selection of closures a few a provided below.
References:
1. Alan Limmer, The Chemistry of Post-bottling Sulfides in Wine, Chemistry in New Zealand, September 2005.
2. Jamie Goode, Finding Closure, Wines & Vines, August, 2008.
Additional Reading:
1. Bruce Zoecklin, Factors Impacting Sulfur-Like Odors in Wine and Winery Operations, 8th Annual Enology and Viticulture British Columbia Wine Grape Council Conference, July 23-24, 2007.