Originally Posted by bwomp313
. . . . . if you continue to use it after that will it be "bad" meaning putting out off flavors or fermenting slowly, whatever? Or does that just mean that it'll no longer be the same strain?
Possibly all or none of the above, it all depends on how you maintain the yeast, when you harvest it, what temperatures you ferment at, what adjuncts you ferment the brews with, etc, etc.
If someone gets into this, I suggest saving a sample of your initial yeast for propagation after a few generations. Unless of course you are trying to mutate it.
That being said, there are companies (breweries/distilleries) that have maintained a specific strain (or blend) of yeast for 10's of years, maybe 100's. It all depends on the effort you can afford to put into it.
Other interesting info: Some strains come from other strains or blends, for instance, I've read that the Duvel strain (Like white labs WLP570) was isolated from the 20 odd strains in the McEwans yeast (White labs WLP028, Wyeast 1728, etc) at Moortgarts in the 1940s I believe