Long-term Viability of Yeasts

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gitano

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I have been reading here of late that one should not expect to keep yeast saved from a given home-brewed batch more than about 6 months. Longer than that and it has "lost all of it's viability". That alone made me scratch my head a little 'cause my experience with yeast is that the blasted stuff is difficult to KILL! When I thought about the sourdough batches that last for decades and the famous "San Francisco sourdough" that is reputed to be over 100 years old I was still scratching my head.

I thought maybe the difference was that the yeasts in sourdough are being constantly fed, while the 'saved' yeast might be "starving". Then I read this thread: https://www.homebrewtalk.com/showthread.php?t=588216

So, here I am asking someone to 'splain to me the profoundly short duration of viability of only 6 months reported for "beer" yeasts salvaged from home-brewing a batch of beer.

It's not a rhetorical question.
I'm not trying to "stir" ANY "pot".
I have no ax to grind or hobby horse to ride.
I don't think anyone is "wrong".
I simply don't understand how when yeast is 'salvaged' from making a batch of beer that its viability approaches zero in 6 months, but yeast found in bottled beer can live for "hundreds of years". (Actually, I'd settle for "just single-digit years", in contrast to 6 mo.)

Thanks,
Paul
 

DurtyChemist

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Wasilla....my wife is from there.

SOOOO my oversimplification and short summary of the whole subject is 100% of the yeast from a batch won't die but what WILL die is the diversity. You'll have a much smaller representation from the original population but you'll still have yeast. This can be seen from all the threads on this forum over the YEARS of "brought my yeast back from X months/years old" and harvesting bottle dregs.

I believe the 6 months comes from the current information saying the viability redues from the original population and it's easy to buy a new pack of yeast from the store after 6 months...unless you live in Wasilla and you're limited to purchasing yeast in A-Town or asking the local breweries for some of theirs.
 

Yooper

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The viability of the yeast does become reduced- partly because of the number of yeast cells that are dormant (they can autolyze) but there are still a lot of them alive.

The issue for me saving yeast long term is that microbes can grow and it's not a sterile medium (unless you're yeast ranching and using slants and agar) so it's more than it's not 100% pure fresh yeast in the jar than the yeast cells all die.
 
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gitano

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I'm "fine" with those explanations, and since I am able to 'read between the lines', I have an answer.

A little off-topic, but my curiosity is piqued by "yeast slants". I think I might have to do that.:) "Saving stuff" especially 'genetic material' like seeds and in this case yeast, is something I 'do'.

Thanks for the replies,
Paul

PS - Fortunately, I don't have to go all the way to Los Anchorage to get most brewing supplies. A new LHBS has opened in Wasilla this spring. A nice, unpretentious, helpful bunch of fellows actually. I hope they are able to stay in business longer than other Valley LHBSs have.

Paul
 

Stillraining

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One other thing to consider is that yeast can mutate along the way as well. By batch 6 or 8 I'm getting some different flavors then I did with batch 1. But I dont wash either so that might be the cause... I have also noticed a change in flocculation with some yeast too, as in not getting better but worse.
 

brewcat

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Just an interesting aside:

I have read of bakers that start new sourdough starters and discard old ones (even if they are 100 years old). It removes any notion of magical starters, basically leaving flavor up to the baker. I currently have my own that I have had for about 5 years. I try to feed it once every couple of weeks but sometimes it gets up to a month. I haven't noticed degradation. So from that...

I don't know what it would take to keep yeast longer for brewing. It would seem you would have to have a master flask and then have a starter flask from that. You would feed your master and pull a little off and feed the starter to use for brewing. I think you would still need at least a 3rd flask, so you are constantly pulling from fresh yeast. Any master would never be used for brewing.
 

55x11

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I have been reading here of late that one should not expect to keep yeast saved from a given home-brewed batch more than about 6 months. Longer than that and it has "lost all of it's viability". That alone made me scratch my head a little 'cause my experience with yeast is that the blasted stuff is difficult to KILL! When I thought about the sourdough batches that last for decades and the famous "San Francisco sourdough" that is reputed to be over 100 years old I was still scratching my head.

I thought maybe the difference was that the yeasts in sourdough are being constantly fed, while the 'saved' yeast might be "starving". Then I read this thread: https://www.homebrewtalk.com/showthread.php?t=588216

So, here I am asking someone to 'splain to me the profoundly short duration of viability of only 6 months reported for "beer" yeasts salvaged from home-brewing a batch of beer.

It's not a rhetorical question.
I'm not trying to "stir" ANY "pot".
I have no ax to grind or hobby horse to ride.
I don't think anyone is "wrong".
I simply don't understand how when yeast is 'salvaged' from making a batch of beer that its viability approaches zero in 6 months, but yeast found in bottled beer can live for "hundreds of years". (Actually, I'd settle for "just single-digit years", in contrast to 6 mo.)

Thanks,
Paul
For what it's worth, I believe many online yeast viability underestimate the viability - some drop off to zero very abruptly, which just cannot happen naturally. For example, brewers friend calculator will tell you your 4 months old yeast has 15% viability. While 5 months and beyond give you... 0% viability.
So it takes 70 days to lose half of your cells. So in another 70 days you would expect 25% viability (another half is gone) - instead calculator tells you viability drops by a factor of.. 50! Down to 1%:
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

Instead I believe the decay is more gradual and exponential, as this article details:
http://beersmith.com/blog/2010/12/14/yeast-starters-for-home-brewing-beer-part-1/

For practical purposes it tells me that reusing yeast is definitely practical for 4-6 months yeast as long as you make sufficient starter (I used 4-5L) and harvest more than a vial's worth of yeast.

Beyond 10-12 months it becomes more dicey, unless you are willing to step up your starter a few times with large starter - otherwise you are probably under pitching, perhaps severely.
 
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gitano

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"
But I don't wash either
" Yikes!;)

"Mutation" is a 'viable' :) point, but what's good for the goose is good for the gander. Meaning that same mutation reasoning would apply to those other 'long-viable' yeast sources as well.

I think like most things that one does 'creatively', one finds that level of detail or precision with which one is comfortable and operates in that particular 'comfort zone'. Sometimes it's good to get bumped out of one's 'comfort zone', but as a rule, we do our best work when we use procedures with which we are familiar.

Thanks,
Paul
 
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