Dear Wine Wizard,

Here’s one problem you may have been asked about before. My finished wine has an aroma and taste of rubber and burnt toast, a bit like burnt rubber. Since I will be making more wine this year, I sure would like to know what I’m doing wrong. Would you let me know?

Richard Larocque
L’Orignal, Ontario

The Wine Wizard replies: I can think of two possible causes of these flavors and smells. The first is over-oaking of your wine with highly toasted chips. If you are using chips, run bench trials to see what level of oakiness you like. Take small samples of your wine and add oak chips at varying rates. Taste the wine and see what level you best enjoy. If this is too involved, play it safe and go with a low rate like 1 g/L.

The second possible cause is hydrogen disulfide or mercaptans. There are numerous potential pathways for these stinky compounds to get into your wine. Sulfur spraying in the vineyard too close to the harvest date is one possibility. Yeast spit out elemental sulfur in the form of hydrogen sulfide. Other causes might include insufficient nitrogen levels during fermentation, high fermentation temperatures, low fermentation temperatures, a too-rapid fermentation or anything that will stress your yeast out. Most often, hydrogen sulfide smells like rotten eggs and mercaptan smells kind of oniony, but I’ve seen them develop into burnt rubber aromas in finished wines.

Two possible solutions to this problem are aeration or adding copper sulfate. While the wine is still fermenting, you can try aerating it, but don’t aerate after fermentation is complete. Alternately, you can add copper sulfate, which binds to hydrogen sulfide. Copper sulfide should only be used at concentrations lower than 0.5 mg/L (ppm). (I discussed this in more detail in the Winter 2001 Winemaker.)

Sometimes hydrogen sulfide and especially mercaptans can’t be removed at all and even professional folks have to live with the stinky results of naughty yeast. Never fun, but a reality of the business.

For more of the Wine Wizard’s wit and wisdom, pick up the latest issue of WineMaker, now available at better winemaking shops and bookstores throughout North America.