One hell of a lunch tasting.....

[Randy Caparoso]

Sorry, but I don't think so. What you've experienced is probably temperature service variation. When a Riesling warms up, whatever petrol characteristics (and any other qualities, good or bad) that are part of the wine itself becomes more detectable to the nose. That's why you don't want to drink really good wine too cold, and lousy wine as cold as possible!