Mercaptans

In the early part of this week a French chemical factory in Rouen accidentally released a cloud of methyl mercaptan gas into the atmosphere. Mercaptans are some of the smelliest substances known to man. Humans can literally smell them at a few parts per billion concentration. This is why mercaptans are injected into natural gas which is normally odourless so that we can smell gas leaks. Mercaptans are harmless.

On Tuesday evening the gas had spread to the UK and my wife and I could smell it in the atmosphere when we went for a walk. My wife smelt it first. It felt like we were walking through a large gas leak.

http://www.huffingtonpost.com/2013/01/22/french-bad-smell-mercaptan-rouen-france-foul-odor_n_2525587.html

What has this got to do with wine you may ask. Well  methyl mercaptan and ethyl mercaptan can sometimes be smelt in wine as they are both by-products of the "reduction" of sulphur compounds. These sulphur compounds are present both naturally and artificially in the wine.

Burgundy Red wines are particularly prone; there is often a slight aroma of rotten cabbage, or even shit - if you pardon the expression. Methyl Mercaptan is produced in the human digestive system. Some wine commentators regard the presence of methyl and ethyl mercaptan as being a wine fault which should be eliminated. Others regard it as being part of the character of a wine. My wife and I are of the latter view.

We have both enjoyed aged Burgundies which have a very slight scent of rotten cabbage amongst the complexity of other tastes and aromas. If it is a fault then it is very difficult to get rid of it without letting some oxygen into the wine "to reverse the 'reduction'". Oxidation creates its own problems so there is a fine balance here.

Even though mercaptans can be detected on the nose at extremely low concentrations some people are not sensitive at all. They must be the lucky ones unless they have a gas leak or are partial to some older types of Burgundy



http://www.wineanorak.com/mercaptansinwine.htm

http://napavalleyregister.com/lifestyles/food-and-cooking/wine/columnists/dan-berger/identifying-wine/article_19a639b2-508e-11e2-8c96-0019bb2963f4.html