When I get a new vial, I usually make a starter, and split it into two bottles. One goes into storage, and I'll take the other one, pitch it, and pitch the remaining yeast cake maybe 3 or 4 times. After that I just get too nervous about contamination. And quite often I want to make a different beer that requires a different yeast. When I'm ready to go back to that original yeast, I'll take that second starter that went into storage, build that up and depending on how energetic I feel, I'll save some of that into another bottle that'll go into storage and pitch the rest, take that 3 or 4 times, etc etc. Needless to say, I don't buy yeast very often.
However, I realized that I had a couple of bottles of wlp007 in the yeast fridge. I haven't used that in a while, it went into the fridge August. Hmm. Probably dead, but heck, let's try to build it back up. Poured off the liquid, shook up the yeast on the bottom, poured it into a flask with a little bit of basic wort. Sat it on the stir plate over night. Next morning, looks nice and cloudy, was about to wash the yeast (since it had been sitting around for quite a while and there's probably tons of dead yeast in there that I didn't want to contribute to off flavors if I pitched it) and took a whiff .. WHOOOO. That isn't yeast that's growing in there. If you've ever done the off flavor tasting kit from Siebel, this is straight from the vial of ethyl acetate. If the girlfriend was around I would've had her put her finger in it and I'm guessing the nail polish would've dissolved right off. I'm not entirely sure what causes it, but needless to say, it went down the sink. And i've sanitized my equipment. Twice.
Lesson: If it doesn't smell like yeast. Don't use it. Six bucks for a fresh vial is worth not ruining a $20 batch of beer.