I have reused the WLP 810 SF lager yeast 6 times and I have to say it is a very hearty yeast. I brewed commons (2), APAs (2), and two FauxPils.
I am going to try to top this one with Dry English WLP 007, since my new favorite brewery (Jester King from TX) uses it.
I’ve regularly taken WY1968 through more than nine repitches with no problems whatsoever, producing a variety of different beers (it particularly makes a really beautiful Porter).
I currently have a sixth generation ferment going with some Old Newark ale yeast happily munching away at a Burton/Barleywine.
I also have a porter currently fermenting, using my house yeast… the 8th repitch for that one.
I used to really push things and repitch an insane number of times (20+), but nowadays I pretty much stop at around 9 or 10. I never had a problem, and they seem like they can keep going, but I figure maybe I shouldn’t press my luck. It’s easy enough to culture up a fresh crop.
I usually stop at 5 generations or less, but I stretch one vial/pack for a very long time as I split the cake into thirds each time, so its exponential - I think I bought all of 2 packs of yeast last year, yet I brewed 180-200gal.
I don’t technically “repitch” but I do reuse over and over again. When I first buy a yeast, I save some on a slant and reuse from that (and subsequently recultured slants) basically forever. Doesn’t incur the generational mutations that real “repitching” can have and I never have to buy a particular yeast twice. In fact, I haven’t bought yeast in what seems like eons 
Probably 4 generations, mostly due to carboy capacity or desire to use a different strain or excessive time between batches. Depends on the strain. Haven’t had much luck repitching hefeweizen yeast.
I don’t recall going past three generations. Mostly for the same reasons as Gordon.
I’m interested, though, in Gordon’s experience re-pitching hefe yeast. What didn’t turn out right? Any thoughts as to why?
I don’t recall reusing hefe, myself. But I don’t make many wheat beers.
I’ll split the first yeast-cake in half usually and get two or more beers out of it. Normally, I try not to go past a 3rd re-pitch and don’t experience any problems.
I currently have some German Lager yeast that is a 5th generation yeast. I am planning to go for #6. No ill effects as of yet, in fact it recently made some of the best Ofest I have ever brewed. Might as well keep on going with it. :)
Just didn’t like the taste. Not as clean. Only tried it once. Didn’t like it. Don’t often need to repitch hefe yeast, so it’s not something I’d try very often anyway.
I gone ten with lagers. If anything it was getting better. Lagers are less likely to build up contaminates than ales due to the lower temps. I’ll go five with ale.
The fact that “it was getting better” means it was changing, mostly people look at the number of times to repitch because they want it to taste the same. “Better” may just have been a lucky mutation for you. As long as it is still tasting good, keep going though.
I read an article in the ASBC journal a few years ago that looked at serial repitching of lager yeast. They said it was strain dependent, and recommended no more than 7 generations for lager yeast. Ale yeast were twice that if I remember right. Colder may hinder contaminating organisms, but it does not necessarily favor genomic stability. Assuming you are keeping contamination down, the is the biggest factor is that they are different organisms.
better is also sometimes actually because upon repitch, the brewer is pitching a more sufficient quantity of yeast.
I’ve reused the tubes for carrying salad dressing over and over again but have always just thrown the packet away… :-\
I’m worried about hops and trub in the yeast cake when it come to reusing the cake when splitting it up. I don’t seem to brew often enough to reuse yeast, although I’d like to start planning my brews more so that I brew a couple in succession so that I can reuse yeast. Otherwise, I seem to brew about once every 3 weeks, which probably isn’t too long to just direct pitch slurry from the previous batch, but I don’t do for some reason. Maybe I ought to start.
If it had changed or not I couldn’t really say. It still made the beer that I wanted, and I had more than all the yeast I needed. I like to use the fresh yest right out of the fermenter not the stuff I’ve had in the fridge for weeks.
I was just thinking…how many generations does it take if I start with one cell and want to brew say–100 barrels? As homebrewers we probably think too small.
How many batches have I gotten out of a single yeast purchase? I think my 1272 culture is on something like 13.
Repitching from harvested slurry, though, I’ve only done three “generations”. Mostly just because I don’t brew often enough for that to be a time-saver. I’d usually have to make a starter anyway.