I’ve always heard that when repitching yeast that you should limit the number of times you repitch the yeast. Basically, that after x many (Between five and seven batches are the numbers that are coming to mind) batches, you’re better off tossing the old yeast and starting fresh.
What yeast mechanism/health factor/issue drives this? Is it a mutation thing, where the yeast get further away from the starting point? Or do the old, unviable cells begin to take up more and more of the mass of the pitch? Potential for other critters to start to take over?
How could you “resurrect” an old yeast that has seen that many fermentations? Plate the yeast for single colonies and start over?
Commercial breweries go dozens of pitches. I believe the main issue with homebrewers is the limited ability to maintain adequate sanitation compared to a commercial operation ( I know plenty of commercial breweries that suck worse than most homebrewers when it comes to sanitation ).
Bacteria grows faster, repitch after repitch will in theory have higher bacteria counts. At some point the bacteria will tip the scale enough to notice.
If your sanitation is dead solid, and you are able to perform very sanitary yeast harvest procedures, you should be able to go a long time with the same initial pitch.
I don’t worry about bacteria so much (which can disabled through starsan) but I do worry more about wild yeast producing off-flavors which star san does not seem to affect. I have had more issues with off-flavors from yeast rather than bacteria in my years of brewing.
not sure the number of pitches is absolute brewer to brewer. I’ve gone around 8 with no issues, and likely could keep going. i just figure if I get 8 good batches out of one $6-$7 vial of yeast, I’m good so why press it until the point you get a sucky batch.
Agreed. I am currently on repitch #5 with my WY munich strain and all has been good. I do feel that the yeast is getting acclimated to my process and is starting to get pretty predictable in its behavior. Good yeast! Now go ferment wort!
Pro’s use an acid wash to kill bacteria while the yeast survive. I don’t know if the acid wash is a regular practice after X repitches or if only some brewers do it.
Also, yeast budding may play a role in limiting the number of repitches. I saw some stuff on a web search about bud sites leaving scars that can lead to more ester formation.
Ah, but that’s kinda what I’m going for. S. Cerevisiae mentioned that some strains take several batches to “adapt” and start producing the expected flavors. I’m settling down to mostly brewing English styles, and I’m curious how far I can push repitching. Ideally, the yeast will be top cropped, so that ought to leave the bacteria out of the equation. (As I understand it, only yeast will rise to the top.)
That doesn’t eliminate wild yeast however; but I do have an idea I’m pursuing to fix that issue.
And if the esters get way out of whack, then I’ll just plate the culture and start over.