Foiling the bugs that spoil wine

After a long day, nothing beats kicking back on the couch, grabbing a corkscrew and pouring yourself a leisurely glass of wine. And nothing can kill that golden moment like the waft of a “corked” bottle: that musty, moldy smell that wine gets when it has been spoiled by nefarious chemicals that are usually attributed to the cork.

Cork taint is mostly blamed on the compound 2,4,6-trichloroanisole, or TCA, which causes the potent fungal smell in bottles gone wrong. Wine lovers will go to great lengths to rescue their wine from cork taint: one purification method is to let the wine sit in a bowl with crumpled up plastic wrap, to which the TCA molecules stick when the wine is poured out.

But TCA isn’t the only culprit behind cork taint. In 2004, a research group in Australia identified another molecule, 2-methoxy-3,5-dimethylpyrazine, or MDMP, as a pollutant in wine corks. Sensitive noses have called MDMP’s signature scent herbaceous, with notes of potato and green hazelnut, dusty, obnoxiously musty and simply corky.

When MDMP was first characterized (but not in corks) more than 20 years ago, researchers found a bacterial strain that was producing the chemical—but they couldn’t figure out its identity. That has just changed: printed in the Journal of Agricultural and Food Chemistry on December 8 is the work of a French group that has finally identified the MDMP-producing microbe as Rhizobium excellensis (named after the superiority of the lab that discovered it), a previously unknown species of Rhizobium.

Now that we know the source of MDMP, it may be easier to find how the microbe makes it into corks and stop the musty smell in its tracks. The researchers found high concentrations of MDMP in more than 40 percent of the natural cork stoppers they tested, which means that bottlers should probably either better monitor their supply or switch to synthetic corks to avoid the problem. Winemakers may have to make a tough choice between tradition and cork taint.