Greetings,
I've often cloned yeast from bottles of beer I've enjoyed (both homebrew and
commercial), with good results. But I've heard that if you clone the same
yeast too many times, mutations result that affect the flavor of the beer.
A few questions come to mind:
* Is this true?
* On average, how many times might I expect to be able to clone a yeast
colony before it is significantly different from the original strain?
* What is the nature of the mutations? i.e., What sort of flavor changes or
other behavior might I expect? Don't wanna brew no skunky beer :)
* How do the yeast labs (Wyeast, White Labs, etc.) perpetuate their yeast
strains without the same thing happening to them?
* Finally: Maybe mutations aren't always a bad thing. Has any of our group
deliberately mutated a yeast strain so as to "encourage" mutation in a
certain direction?

Best Regards,
Bill Bell

>Is this true?
Yes, it is. More and more cells will mutate sooner or later until they
dominate the batch.
[color=blue]
>On average, how many times might I expect to be able to clone a yeast
>colony before it is significantly different from the original strain?[/color]
AFAIK, starting with fresh and pure cultures, it will begin with the 4th or
5th generation. As the yeast in bottles is already very stressed, the risk
of already defect or mutated cells to take over the batch is IMO higher.
[color=blue]
>* What is the nature of the mutations? i.e., What sort of flavor changes or
>other behavior might I expect? Don't wanna brew no skunky beer :)[/color]
The changes often result in faster und higher attenuations, but with more
esters and/or off flavors.
[color=blue]
>* How do the yeast labs (Wyeast, White Labs, etc.) perpetuate their yeast
>strains without the same thing happening to them?[/color]
They regularly select the strains and seperate mutation from original cell
by cell. Microscopes and sometimes trials help them.
[color=blue]
>* Finally: Maybe mutations aren't always a bad thing. Has any of our group
>deliberately mutated a yeast strain so as to "encourage" mutation in a
>certain direction?[/color]
Not yet, but of course this is right; many wanted and selected strains are
nothing but mutations from other strains...

--
* [url]www.brauherr.de[/url]
* (wenn Bier für Sie nicht nur gelb ist und blau macht)

** Wer das bayerische "Reinheitsgebot" für eine deutsche Segnung hält,
** der sollte auch Michael Glos als Bundeskanzler wählen.

***None of those is translatable without loss.
***I regret, you shouldn't.

On Mon, 14 Jul 2003, Bill Bell wrote:
[color=blue]
> Greetings,
> I've often cloned yeast from bottles of beer I've enjoyed (both homebrew and
> commercial), with good results. But I've heard that if you clone the same
> yeast too many times, mutations result that affect the flavor of the beer.
> A few questions come to mind:
> * Is this true?[/color]
If by "clone" you mean that you isolate yeast from a beer, then
mutations can and do occur. However, you should start with a few cells
from the beer and always select many cells when you restreak the yeast
onto new media. This way, if there is a mutation in a single yeast, you
will be including plenty of other yeast thta aren't likely to have the
same mutation.
[color=blue]
> * On average, how many times might I expect to be able to clone a yeast
> colony before it is significantly different from the original strain?[/color]
Depending on the conditions you keepm them under, you could keep yeast
that would give the same flavor profile long enough to give to your great
grandkids. (Probably could keep them indefinately)
[color=blue]
> * What is the nature of the mutations? i.e., What sort of flavor changes or
> other behavior might I expect? Don't wanna brew no skunky beer :)[/color]
Mutations are random, but if you don't select a single colony to
make your starter with, the contribution of those mutation likely won't be
noticed.
[color=blue]
> * How do the yeast labs (Wyeast, White Labs, etc.) perpetuate their yeast
> strains without the same thing happening to them?[/color]
Cryogenics. They freeze their yeast to stop biological activity,
i.e. mutatuions.
[color=blue]
> * Finally: Maybe mutations aren't always a bad thing. Has any of our group
> deliberately mutated a yeast strain so as to "encourage" mutation in a
> certain direction?[/color]
Haven't done it yet because there are so many yeast available one
doesn't need to create his own special yeast strain.
Warren Place