Why Some Wines Smell Like Bug Spray

I got one of those 9-1-1 wine emergency calls at about 4 p.m. on Christmas day, a few minutes before we started prepping for dinner.

My friend had just opened a bottle of Oregon Pinot Noir that he had purchased on a recent trip to Willamette Valley, and the wine smelled like bug spray.

"It was totally undrinkable," he said, with the usual distress that accompanies the experience of opening an off bottle, irrespective of the cause. Another bottle from the same case had also been off.

"What causes that [smell]?" he asked.

I’m not sure how that scent manifests itself in wine. In the past few months, my colleague Tim Fish and I have encountered red wines that have had that same bug spray scent.

We've also had a couple of wines that had a strong citronella aroma, reminding me of the kind of candles used to ward off mosquitoes in the summer.

I did some research for possible causes of this taint, which took me down several paths, and finally I got an expert's opinion, which I hereby share.

The expert, Carole Meredith, is professor emeritia at U.C. Davis and she owns Lagier Meredith in Napa Valley with her husband, Steve.

If you can understand her explanation, congratulations. I can't, but it sounds good and is no doubt correct, yet further evidence of how complex the science and chemistry is in wine, especially for us liberal arts grads.

"Steve (more so than me) regularly finds bug spray odors in some Syrahs. (Not ours.)," she wrote. "The smell is most likely caused by a reduced sulfur compound (or combination of such compounds) produced by the yeast in response to a nutrient deficiency in a particular grape source. (I don't know specifically which sulfur-containing compound causes the bug spray smell, but sulfur compounds are involved in many strong odors, e.g., skunk spray, burning rubber, cabbage, garlic, rotten egg, burning match.)"

She went on to explain, "In addition to the sugar that they convert to alcohol, yeast also use other nutrients provided by the grape, including nitrogen, phosphorus, minerals and vitamins. Grape varieties and vineyard sites differ in the biochemical composition of the grapes they produce. The vines may be perfectly healthy but the nutrients in the grapes may not be ideal for the yeast. In some cases that leads to a stuck fermentation, but in other cases the fermentation may proceed to completion but an off-odor may be produced when the yeast metabolic machinery switches to an alternate biochemical pathway to adapt to the available nutrients."

And true to her professional standards, the good doctor offered this cure: "In some cases the winemaker can remedy the situation by supplementing the must with additional yeast nutrients (e.g., DAP or Super food). In other cases, micro oxygenation of the wine can reduce the off odor."

So there you have it—a piece of cake.

Now you'll know how to explain what causes the bug spray scent the next time you're asked.