Gas in Your Glass?
In a tasting of rieslings, at least one person is almost sure to experience what he or she will call a strong “gasoline” or “petrol” smell. Petrol aromas are caused by TDN—trimethyldihydronaphthalene. Several studies have found that the molecule is up to six times more likely to occur in riesling than in other varieties. One of the leading factors responsible for TDN is too much sun exposure on grapes as they grow. With bottle age, concentrations of TDN in the wine actually increase, especially if the wine is high in acidity. Interestingly, cork can absorb as much as 50% of any TDN formed, and thus rieslings stoppered with a screw cap potentially show more TDN than cork-finished wines.