So just to add to this thread, I recently processed a batch that was fermented in the normal way, with airlock etc. I had too much to fit in the jar so I poured it into a mason jar, put plastic wrap over the top, and then a ring lid. It looked great right up until about a week before processing and then started developing some of the yeast. Since it was a small amount and just an experiment, I shook it up and it went away.
When it was time to process, the little jar smelled almost like nail polish remover (acetone?) while the large batch smelled fine. I decided to dump the small batch without even tasting it. It was only about 3 cups. Such a strange smell. Anyone else encounter anything like that? It didn't smell moldy or putrid, just, .....chemical.