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yeast generations and mutations

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twd000

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I don't have any first-hand knowledge in this area, as I just started washing yeast to re-use it for multiple fermentations.

I have heard/read a lot of concern about propagating yeast for too many (although the # differs) generations lest it "mutate" and yield off-flavors in your beer.

I'm sure this is based on some experience, but I can't figure out how it would be a problem in light of other uses of yeast. Commercial and home bread bakers commonly keep a sourdough yeast starter alive for years or even decades, refreshing them by dumping half the starter, then feeding with a flour/water mixture.

How do commercial brewers maintain their yeast? I'm sure they're not buying smack-packs from Wyeast for every batch! Aren't all these yeast strains cloned/duplicated for hundreds/thousands of generations without mutating? Is there some certified pure "yeast bank" in a vault protecting our valuable strains?
 

david_42

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Companies like Wyeast and White Labs do maintain clean yeast strains for commercial breweries.
 
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twd000

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Companies like Wyeast and White Labs do maintain clean yeast strains for commercial breweries.

so aren't the labs then creating multiple generations each time they send the yeast to commercial brewers? is there a distinction between "building" a yeast starter to sufficient volume, and fermenting and washing? what counts as a "generation"?
 

david_42

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The term is used the same as batch. The truth is yeast bud in less than 2 hours.
 

theredben

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Difficult to say how many generations are needed for off-flavours to develop. You can track mutations if you want, but what that means in the real world is not so simple.

LHBS employee has washed yeast for 17 batches in a row. Does it taste differently than when it started? Probably, but it certainly saved him a few dollars. Really up to you in the end.
 
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twd000

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The term is used the same as batch. The truth is yeast bud in less than 2 hours.
so if I understand you correctly, the yeast sold by wyeast and the like are in their thousand-something generation, since they have had to refresh/build the starter in some form to propagate enough to sell to brewers. And we never complain about mutations of lack of quality


Perhaps the limiting factor is STRESSED yeast mutating, while HEALTHY yeast can be propagated indefinitely, for an infinite # of generations with no ill effects?
 

ultravista

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But how do you know if your yeast is / was stressed at some point. Other than the taste of the last batch, how would you know?

Also, when repitching washed yeast, how much do you pitch? With the many yeast washing threads here, the process yeilds about 4 jars of yeasty liquid. Do you pitch one jar or??
 
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twd000

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But how do you know if your yeast is / was stressed at some point. Other than the taste of the last batch, how would you know?
I wouldn't have any way to know. But the commercial yeast labs have obviously figured out a method for propagating yeast indefinitely without ill effects. I'd be interested to see how they compare to the washing/harvesting methods discussed on HBT.

Also, when repitching washed yeast, how much do you pitch? With the many yeast washing threads here, the process yeilds about 4 jars of yeasty liquid. Do you pitch one jar or??
I take one of the 4 jars and build it to a starter size before pitching into the new batch of wort. I'm theorizing that I would just harvest one jar of yeast and re-use it indefinitely with no negative effects, but I haven't tried it enough times yet to know for sure.
 

Calder

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Yeast companies isolate single cells and grow populations from that. That way they can get the pure strain.

What you are doing is slowly changing the yeast, selectively taking certain yeast over the whole population. For example (and this is very simplistic), if you take from the Primary, you are taking the yeast that did the early work and flocculated fast. If you take from the secondary, you are taking the yeast that took a long time to do it's work and didn't flocculate fast.

You see how you can start to be selecting certain yeast cells.

If you rack off the primary too early, you will get the yeast the finished early .... fast ferment but lower attenuation.
 
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twd000

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Yeast companies isolate single cells and grow populations from that. That way they can get the pure strain.

What you are doing is slowly changing the yeast, selectively taking certain yeast over the whole population. For example (and this is very simplistic), if you take from the Primary, you are taking the yeast that did the early work and flocculated fast. If you take from the secondary, you are taking the yeast that took a long time to do it's work and didn't flocculate fast.

You see how you can start to be selecting certain yeast cells.

If you rack off the primary too early, you will get the yeast the finished early .... fast ferment but lower attenuation.
this is the best answer I have seen. So even though yeast use asexual reproduction, the child cells have different DNA than the mother?
 
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The labs are much better equipped to generate new generations of yeast without stress and they also have the microscopes and whatnot to get in there and look for mutations, bacteria, etc. in samples. They are much better equipped to keep a clean strain than many of us (certainly better than me). I also assume they have a frozen bank in which they can take a very, very small sample and build it up into a large sample that gets sent to breweries, packaged in a batch, etc.

You could probably email them and ask.
 

corax

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With repeated batch-to-batch propagation you have more to worry about from accumulation of contaminants than you do from mutants.

The suppliers don't have to worry about either because they can freeze their stocks indefinitely, starting new batches from very small amounts of the pure stock-- thanks to exponential growth, no batch needs to propagate through more than some few tens of generations.
 

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I have a family member who used to work in quality assurance for a large commercial brewer. He recently recommended to me washing every 5-6 generation of your strain with a very light and very diluted acid, then of course rinsing. The process on a home brewing scale takes days repetitively chilling to decant and cleanse. I wish I asked the PH because this was exactly the type of thing he did for years.
 

kanzimonson

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Another point is that Wyeast and White Labs grow yeast, while brewers make beer. Making beer is not the healthiest activity for a yeast's life cycle. They would much rather have access to oxygen and not be exposed to alcohol so they can respirate rather than ferment to get their energy. So brewers are growing stressed yeast.

Also, even the most high tech breweries still have contamination issues because most don't grow up from a single cell. So between exposure/growth of microorganisms and stressed yeast, it makes sense that there is a finite number of times we can repitch.
 

Ichthy

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With repeated batch-to-batch propagation you have more to worry about from accumulation of contaminants than you do from mutants.
I think this is the most important issue with yeast washing.

I'm no expert, but everyone on the boards talks of mutations etc. and I suspect that this stems from reading Palmer's "how to brew". That chapter of the book isn't heavily cited, thus I take most of the selection and mutation talk with a grain of salt.

Maybe the new yeast book by White and JZ answers some of these questions with more scientific backing?

IMO, keep washing and reusing yeast until you can detect a flaw in quality.
 

kanzimonson

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The new yeast book does address some of this. It has a heavy slant towards overall yeast health. Just like humans, when yeast don't have all of their nutrients they can still perform, but not as well.

The most significant mutations it talks about deal with yeast losing their ability to consume sugars as well, or TOO well. I didn't get a full understanding, but it seems that this once again results from "stressed yeast" (loosely defined as undernourished and stressed environment).
 

ultravista

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I wonder if you could use vinegar or even Star San as they are both acidic.
 

Randar

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Another point is that Wyeast and White Labs grow yeast, while brewers make beer. Making beer is not the healthiest activity for a yeast's life cycle. They would much rather have access to oxygen and not be exposed to alcohol so they can respirate rather than ferment to get their energy. So brewers are growing stressed yeast.

Also, even the most high tech breweries still have contamination issues because most don't grow up from a single cell. So between exposure/growth of microorganisms and stressed yeast, it makes sense that there is a finite number of times we can repitch.
As you note, yeast reproduce and grow best in the presence of oxygen and via aerobic activity (vs anaerobic activity used to produce ethanol)...

Acid washing is done by some breweries after every batch and this is their "washing" method. They don't perform similar processed to the distilled/RO water washing that some homebrewers use.

As also noted in this thread, WYeast and White Labs both supply large volume yeast starters to breweries as well as offer yeast storage/housing/isolation for proprietary or house yeasts, so it's not like they are just culturing bottles and selling to homebrewers.

One interesting note in the new book I saw was that brewing yeast does not "breed" like wild yeast can. They simply reproduce via replication and budding and Ale yeast can bud roughly 30 times before expiring and lager yeast around 20 times.
 

Ichthy

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I wonder if you could use vinegar or even Star San as they are both acidic.
There was a link posted above from the whitelabs website. They recommend using phosphoric acid, so starsan should be fine.

If I'm interpreting their article correctly, you should build a starter from wash yeast and once it's finished add enough acid to reach a pH of 2 (the no-rinse concentration of star san). The article then says to continually stir the culture.

So, I'm thinking of making a starter with washed yeast. Chilling and decanting once the starter is done. Then add enough premixed starsan to thin the slurry. Place the the starter back on the stir plate to mix for the recommended 60-90 min.

Does anyone see an issue with acid washing in this manner??
 

kanzimonson

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I think your methodology is fine, but I'm not convinced it's worth doing this on the homebrew scale. Because of the number of transfers we have to do in homebrewing, there's still room to pick up some contamination after you've washed the yeast. Plus, I'd be surprised if the washing eliminated all of the bacteria. You're really just prolonging the inevitable. While getting a few more uses out of your yeast and saving a few bucks is nice, my personal rule is if I ever feel ANY doubt about my culture, I buy a new one. Even if I have no evidence to back up my negative feelings.
 

Ichthy

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I don't have an HBS close by, well not one worth patronizing, so prolonging the inevitable is good for me. :)

I may give this is shot and will report back if I do.
 

ldave

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There was a link posted above from the whitelabs website. They recommend using phosphoric acid, so starsan should be fine.

If I'm interpreting their article correctly, you should build a starter from wash yeast and once it's finished add enough acid to reach a pH of 2 (the no-rinse concentration of star san). The article then says to continually stir the culture.

So, I'm thinking of making a starter with washed yeast. Chilling and decanting once the starter is done. Then add enough premixed starsan to thin the slurry. Place the the starter back on the stir plate to mix for the recommended 60-90 min.

Does anyone see an issue with acid washing in this manner??
While Starsan is phosphoric acid based (50%), it also contains dodecylbenzenesulfonic acid (15%). This component is in the family known as 'sulfonimides', and, thus, is a powerful anti-life agent. There is much more to its killing power than simply low pH, unlike phosphoric acid. Using it to yeast wash would be an interesting experiment. I suspect a near 100% kill rate of everything in the flask. Have you done this experiment?

BTW, the reason I know alot about Starsan is because I'm sensitive to the sulfonimide component of it. It makes me extremely sun sensitive (major itchy rash). I had a pretty miserable summer the year I started using it until I figured out that I had to wear dairyman's gloves when working with it (0% exposure).
 

fpweeks

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Read through the sticky on Slanting Yeast. There is some good info in that thread on how to propagate a heathy strain of yeast, propagating form a starter, etc. Also the last few chapters of the White/Jamil yeast book talk about this as well.
 
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