One of the main reasons for Vinomaker wanting to make Chenin blanc this year was a challenge from a fellow winemaker to participate in a 2009 'ferment-off'. This winemaker had given us a bottle of his 2008 Chenin blanc to drink and also the contact information for the grower. We chilled the wine down. It seemed nice at first, well balanced acid, nice fruity esters and then, as it warmed up, bam! Cabbage!My tasting descriptors tend to be of the first thing that comes to my mind and this time, like one of the veggies in a good Sunday roast, cabbage it was. Vinomaker got more bad eggs than cabbage, so he initially identified the problem as H2S, or more seriously methyl mercaptan. H2S produces smelly, odoriferous sulphur compounds that may have developed in the wine because of poor fermentation practices. Time for the old copper penny routine.
A United States one cent piece, pre-1982, is 95% copper...drop one into a stinky wine and The Great Emancipator frees the bonds of sulphurous servitude and undesirable compounds. The metal in the coin reacts with the H2S in the wine, converting it into insoluble copper sulphide. It is rather rapid chemistry and what it usually means is that the previously stinky wine is now drinkable.
However, that was not the end of this little malodorous matter, the wine had actually moved beyond that and the problem was one of the compound methyl mercaptan. Vinomaker, where are you?
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Sulfur compounds develop in wine both during fermentation and later in finished wine, despite good winemaking techniques and careful bottle storage. The cabbage we noted is only one of a number of sulfur compounds that can be detected at low levels, in this case .3 parts per billion. Some of these compounds can be appropriate for a particular wine type, such as black currents in red wines, suggested by dimethyl sulfide. Others containing ethyl groups such as diethyl disulfide result in rubbery or garlicky notes which are difficult to overcome when tasting. Once discovered in finished wine, only some of these compounds can be treated with copper sulfate to move the compound to one less offensive. These compounds should not be confused with the sulfites added as a preservative that generally do not cause these problems.
Thud, I hope Vinomaker made it a little clearer for you.
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