Also, I wonder where some of this opinion on only using yeast for so many generations comes from? Is yeast really mutating and becoming bad or is it getting infected?
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What is the longest you have gone re-pitching the same yeast?
~25 generations probably, and only started over then because I wanted to change to a different yeast as my "house strain." I know of homebrewers who've been using the same (especially lager) yeast for years, and commercial breweries do it too. Brooklyn Brewing has been repitching the same ale yeast, without reculturing, since Garrett Oliver took over in January 1996. Yes, yeast is probably mutating all the time, but what it is really doing is adapting, without mutating, to your actual brewery conditions. Very few mutations will be detrimental, as in any living thing. A rare one will be beneficial, and most irrelevant. And it is inconceivably unlikely that a mutation in one, lonely, little cell will allow its progeny to outcompete, outlast, and replace your entire population. Brewing yeasts are very stable, that's how we have individual, identifiable strains. If sanitation is strictly observed (as you suggested, infection is the real danger,) there's no reason to start fresh all the time (nor to repitch ad infinitum if you don't want to,) and you will find that yeast rarely performs at its best and expresses its true character (the characteristics you read in a description that made you chose it) until around the 3rd to 5th generation. Give it a go. See if it's for you. Good luck, and happy brewing!