A few months ago I started transferring my fermenting beer into a purged keg with 3-4 to go before reaching a predicted FG. I re-pitch my harvested yeast 8-10 times. Since by transferring before FG is reached and harvesting the yeast that has dropped out of suspension at that point, I am selecting yeast that has flocculated early. My questions: am I likely to see any change in behavior from the yeast I am harvesting early, ie: yeast dropping out of suspension earlier and earlier ? Or is this something that would only be an issue with many more re-pitches.
While it seems logical to reach that conclusion, I highly doubt it, based on my experience with non-spunded repitching. Several years ago, I took a lager yeast out to 25 successive batches without issue (over 2.5 years). I didn’t have the spunding aspect in my situation, but I wouldn’t conclude from your situation that the yeast that you harvest have less vitality, just because of floccing out before the final points are dropped - however, if you also were fermenting under pressure for the full primary fermentation, then my conclusion would differ, as the pressure should have some affect on vitality and suppressive effects, generally. I would expect some potential for genetic drift in a pressurized fermentation set up, less so with mere harvesting than spunding.
But, try it out and let us know your results!
I suspected this very thing a while back due to very slow finishes on the last 4 to 6 gravity points. It turns out that it was due to having too much residual sulfite after oxygenating. I was at 30 ppm and have since reduced to 10 and that solved the problem.
Well, I haven’t had any issues, so far, with re-using the yeast that I have collected at the time I spunded. It does seem logical that if I continually select yeast that floc before FG is reached, that at some point a majority of the yeast cells would floc before FG is reached. Perhaps that change would take hundreds of re-pitches and I’ll never see any change in the limited number of re-pitches that I normally do. Mostly just curious what other brewers thought about it.