Yeast "Generations" question

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I keep seeing that people only "re-use" yeast up to 4 generations. What happens after 4 generations?

Also, if I washed a yeast cake and create 6 batches, I can use those 6 batches 3 more times effectively getting 19 batches out of one? What if I used the yeast cakes from those 6 batches creating 6 more batches of each 2 more times..........you see what I am getting at.

Anyway, I need some understanding. Also, how do the yeast vendors do it?
 
mutation is what happens.

Yes to making 19 from one

I think the vendors always go back to the source sample and propagate from that.
 
Long story short: As yeast divide, they acquire mutations. Over many, many divisions, the mutated yeast strain no longer acts like the original strain of yeast. 4 generations (which is a misnomer...I think you mean over 4 fermentations), is a general guideline where people have observed the yeast no longer acting like the original strain (over- or under flocculating, changes in attenuation, etc.)

Furthermore, stress on the yeast can increase the rate of mutation and you may begin to see changes even sooner than 3-4 fermentations.

What you propose with splitting your yeast cake is fine...just keep in mind that when carrying that batch of yeast from one batch to another it is changing.

Yeast vendors maintain "master banks" of the parent yeast strain and can also re-isolate yeast to re-crete strains that have fermentation characteristics known to that strain.

Hope this helps.
 
maida7 said:
mutation is what happens.
Click to expand...

I think the main concern for the homebrewer is contamination. Mutation would require more adverse conditions and selective propogation over many generations. Somebody pointed out this paper a while ago:

Long Term Serial Repitching and the Genetic
and Phenotypic Stability of Brewer’s Yeast

Here we demonstrate
that while there were some changes to the macromorphological
characteristics of an ale strain over the
course of 98 serial repitchings, there were no genomic
variations or changes to fermentation characteristics.
Similarly, fermentation analysis, flocculation assessment
and genetic fingerprinting of nuclear DNA showed that
there were no significant differences between fresh lager
yeast and the same strain after approximately 135 generations.
Click to expand...
 
broadbill said:
Long story short: As yeast divide, they acquire mutations. Over many, many divisions, the mutated yeast strain no longer acts like the original strain of yeast. 4 generations (which is a misnomer...I think you mean over 4 fermentations), is a general guideline where people have observed the yeast no longer acting like the original strain (over- or under flocculating, changes in attenuation, etc.)

Furthermore, stress on the yeast can increase the rate of mutation and you may begin to see changes even sooner than 3-4 fermentations.

What you propose with splitting your yeast cake is fine...just keep in mind that when carrying that batch of yeast from one batch to another it is changing.

Yeast vendors maintain "master banks" of the parent yeast strain and can also re-isolate yeast to re-crete strains that have fermentation characteristics known to that strain.

Hope this helps.
Click to expand...

It would be fun to do some experimenting with yeast. Like trying to turn a top-fermenting ale yeast into a bottom-fermenting lager yeast by gradually lowering the fermentation temp over several fermentations, in which you keep reusing the yeast cake. Or doing several half gallon batches and re-using the yeast from the batch with the greatest attenuation, and then repeating over and over again until you got a strain with a very good attenuation.
 
I agree that contamination is the bigger risk for the homebrewer than mutation. Sure, mutations happen, but generally to match your environment. This is how great strains have evolved around the world, so it isn't necessarily a bad thing to let it mutate.

Cheers,
Scott
 
There is no hard and fast number of times that you can reuse yeast. It all depends on your brewing practices and how you treat it.
 
Pick said:
Could the yeast get BETTER as it mutates?
Click to expand...

Over enough time, natural selection dictates that they will get better for their environment. Whether that environment is better for making beer is a roll of the dice, and the odds are against it given that the strains we are using are already highly adapted beer-making organisms.
 
So theoretically, if I stored my washed yeast in sealed containers in the fridge, how long might they last? Supposing, of course, that I made starters prior to pitching.
 
If you wash yeast properly too, all you're doing is gathering the meanest, sleakest most bad-ass yeast still left in suspension.
 

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