number of times yeast is re-pitced

Here's an interesting study that challenges the practice we homebrewers use of not re-using yeast after just a few times.

They report no changes after 13 serial re-pitches and in another study, they found no appreciable difference after re-pitching a lager strain 135 times.

Also mentioned is that shape of fermented doesn't really effect the beer.

http://www.scientificsocieties.org/jib/papers/2009/G-2009-0730-597.pdf

from the journal of the institute of brewing. Vol 115 No 2. 2009

this seems to be further backed by this study from 2007:
http://www.scientificsocieties.org/jib/papers/2007/G-2007-0420-478.pdf

Wow. That's fantastic info.

I'll have to forward this onto a local microbrewer, last I heard he was on 20+ generations and was worried it had/would mutate, it was an interesting discussion with a bunch of homebrewers... the consensus amongst us was if it tastes good, ferments well and floccs well, why not keep using it. When you have 25 barrels on the line it's a little different than making the decision to repitch as a homebrewer.

I never go over 5 repitches. The main reason is because I am paranoid about contamination and I am not working with a closed system like pro brewers are. I don't get too concerned about mutations because I am very careful with my yeast propagation, ferment temps and supplying proper nutrients. If I had a clean room or somewhere that I could move the yeast about with no fear of contamination I would probably go quite a bit more.

Tonedef131 said:

I never go over 5 repitches. The main reason is because I am paranoid about contamination and I am not working with a closed system like pro brewers are. I don't get too concerned about mutations because I am very careful with my yeast propagation, ferment temps and supplying proper nutrients. If I had a clean room or somewhere that I could move the yeast about with no fear of contamination I would probably go quite a bit more.

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Agreed, this is more pertinent to larger scale brewing:

- Less chance of contamination due to the closed system and large volumes;
- Yeast is stored for short periods of time, if stored at all, before re-pitching;
- Wort gravity and composition is consistent across re-pitches;
- Fermentation temperature and length is consistent across re-pitches.

I only re-pitch for 2-3 generations before rebuilding from a slant.

Exactly, I have never met a pro brewer who keeps yeast around more than 4 days...and I have talked to a lot of them about it. For a homebrewer it is rare to be brewing often enough (and/or close enough styles) to be able to repitch that soon. I get very excited when I get a chance to repitch the day I rack off the cake, but in reality it is more like a week between beer removal and repitching. If it's spends more than two weeks in the fridge I won't reuse it, it's not worth risking a batch of beer and you have basically sacrificed all the advantages of repitching.

You're definitely playing it safe by not re-pitching your yeast after being in the fridge more than 2 weeks. However, that's not to say that your yeast isn't still viable and able to be used in your next batch. I have washed yeast from several months ago that is going strong in my most recent batch. This yeast is from a strain I purchased last year and has been washed at least 4 times resulting in 4 mason jars of yeast each time. Haven't had a problem with infections, off flavors, lower attenuation, etc. yet. Proper sterilization is key I believe in making this possible. As long as you are careful with your sanitization/sterilization, you should have no problems keeping yeast for months on end.

rsmith179 said:

You're definitely playing it safe by not re-pitching your yeast after being in the fridge more than 2 weeks. However, that's not to say that your yeast isn't still viable and able to be used in your next batch.

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Yeah I know it can be grown back up, but to me the biggest advantage of repitching is having a very active slurry of viable yeast ready to go. Once their viability has dropped to 50% or so I would have to make a starter to grow them back up and if I'm doing that I am just going to get a fresh pack/vial.

Honestly it's probably a lot more pragmatic to grow it back up, I'm just paranoid about contamination. I have never had a problem with infection but I just don't trust my kitchen/garage/bathroom/any other place in my house to handle yeast.

Tonedef131 said:

Yeah I know it can be grown back up, but to me the biggest advantage of repitching is having a very active slurry of viable yeast ready to go. Once their viability has dropped to 50% or so I would have to make a starter to grow them back up and if I'm doing that I am just going to get a fresh pack/vial.

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Agreed, and viability is about 50% after 2-3 weeks. So I won't repitch past that point anymore either. I simply had too many problems with old yeast autolyzing and ruining batches (that has happened twice now... rubber meat beer!) or excessive lag times followed by sluggish fermentation even though I pitched a suitable starter. I have much better luck building up fresh yeast from a slant.

Ok, say that we as homebrewers are able to completely prevent yeast contamination, why would it not be okay to keep the yeast stored in a sealed, sterile invironment? How is us storing in a sterile environment different than buying sealed yeast from the lab that has been stored for a few weeks? On a different note i read an article published by John Palmer stating that Ale yeasts can be repitched an unlimited amount of times but required ~25-50% more cells to achieve the same job Vs newly propagated yeast. On the other hand, Palmer recomended not repitching a lager yeast more than 15 times, but did not give a reason why. Just reciently I've been pouring the cake from my carboy to a sanitized 22oz bottle and capping/storing in the fridge. I have yet to use any of these reclaimed yeasts mostly because I'm using so many different strains. happy brewing

When I started brewing, I was very gung-ho about reusing yeast, washing it, saving it, etc. Then I realized that the amount of time and energy I spent trying to save money on yeast wasn't worth the $7 smack pack.
That said, I do plan my batches to reuse some yeast directly from the fermenter to pitch. Once I get 2 or 3 uses from a smack pack, I want to move on to another yeast anyway.