And for what it’s worth, I have taken a lager yeast out 25 repitches with no observed off flavors or performance issues. It took a couple years and I stopped only because I felt I had satisfied myself and wanted to move onto other strains.
That's good to know. I've never gone that far, simply due to fear of the unknown. Around 10 generations has been the max for me. But armed with this info, we will continue to re-pitch without being overly concerned.
My yeast has sat for about 5 months, completely dormant. And then re-pitched without any problems. I try to brew faster and re-use the yeast on a more rapid schedule.
The problem arises when you have three, four, or more yeasts in storage.
I have the following, all being harvested:
London Ale (Wyeast)
Czech Pils (Wyeast)
Oktoberfest (Wyeast Blend)
The only ones not working right now are the Kolsch and the Czech Pils.
We have 40 gallons fermenting at this time.