Last night in my wine business class we evaluated 4 interesting wine from Greece and South Africa. The last South African wine, a deep red pinotage with the distinctive red berry, greenstick, earth and spices that it is known for, also included a very strong smell of rotten eggs. Immediately one of my students suggested we put a penny in our glass, and I agreed. In less than 10 seconds the stinky smell had dissipated in the wine and we were able to evaluate it more fairly. Looking around the classroom, I saw some puzzlement on the faces of other students, so I thought it would be useful to take a few minutes to explain why we put pennies in the wine.
The stinky rotten egg smell was caused by too much hydrogen sulfide in the wine. Sometimes this can form more complex sulfur compounds which are called mercaptans. According to James Halliday & Hugh Johnson in The Art and Science of Wine (2007), “these can assume an ungodly range of totally unpleasant personalities: burned rubber, tar, rotten game, and rancid garlic…..while the taste always has a bitter, astringent finish to add to whatever particular flavor it may have.…It toughens and obscures the taste; in a recently bottled red wine it may be confused with tannins (p. 214.)” NOTE: It is important to differentiate sulfides and mercaptans from brett, which is yeast that gives wine a stinky barnyard and leather taste.
So What Causes the Stinky Sulfur Smell?
There are several causes of hydrogen sulfides and mercaptans in wine, but the primary ones are: 1) using too much sulfur in the vineyard to control powdery mildew, and/or applying it too close to harvest. 2) A second reason may be that the fermentation yeast did not have enough nutrients – in which case they produce more hydrogen sulfides. It should be noted that some fermentation yeasts do this more than others. 3) A third reason could be that the wine did not receive enough oxygen during fermentation, and/or after — with racking (or aerating the wine). 4) Finally if the wine is left to sit for too long on the gross lees, this problem can also occur.
Solving the Problem
The best way to prevent sulfides occurring in the wine is good viticulture and winemaking practices. However, if it happens anyway, the first step in the cellar is to rack (aerate) the wine. This often solves the problem as the sulfides blow away. If the rotten smell is still present, then a small addition of copper sulfate can be added (according to legal limits). This combines with the hydrogen sulfide to form copper sulfide which can then be removed by racking. If none of this works, then the only solutions are to blend the wine with a non-smelly one; remove the off odor with expensive reverse osmosis, or discard the wine.
If you are a wine consumer and you have just purchased a bottle of wine that has the sulfur taint when you open it, the first solution is to aerate it by putting it in a decanter and letting it rest for about 30 minutes. If the bad aroma is still present, add a few clean pennies to the decanter. This will often erase the smell. If that doesn’t work, then pour the wine back into the bottle and return it to the retailer for a refund.