What could make a wine smell like gasoline?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
What causes the petrol smell in some wines?
—Jim H., Simpsonville, S.C.
Dear Jim,
That whiff of petrol, kerosene, gasoline or paraffin that can be found in wines like Riesling is because of a chemical compound known as TDN (1,1,6-trimethyl-1,2-dihydronaphthalene), which can form as a byproduct of a wine’s aging process.
While some might find it strange, I love that distinctive note, especially if it’s in balance with other elements. I’ve heard that it becomes more pronounced in grapes that are very ripe, or dehydrated, but both of those things concentrate all types of notes in wine, not just the petrol ones.
—Dr. Vinny