We all know that yeast, like a virus, will mutate over successive generations.
But how long does this take in the real world? How many generations will remain true to the original? Do mutations automatically mean the yeast will no longer perform?
Is there a chance that a mutant yeast would actually improve in character?
How do you know a yeast has mutated to the point of no longer being viable for beer?
My experience has been that each successive generation will actually perform better than the previous generation, up to a point. Is this the result of mutation?
Yeah too much to unpack here regarding mutation (and genetic drift is arguably a bigger consideration anyway), but a couple of these questions can be fairly easily answered:
How do you know a yeast has mutated to the point of no longer being viable for beer? Unless you want to take up yeast plating and start a microbiology lab in your house, the only way to know is via fermentation performance and flavor profile of a batch using that yeast. EDIT: But also, declining performance/flavor could instead or in addition be due to bacterial and/or wild yeast infection. This is much more likely to be the reason for declining performance/flavor at the homebrew level than mutation. Again, you’d need a lab to distinguish between the two.
My experience has been that each successive generation will actually perform better than the previous generation, up to a point. Is this the result of mutation? No. It is because the cells are fat and happy and healthy because they have been repeatedly and extremely well-fed on the food source they like the most.
I have experienced petite mutants arising in a single batch that was stressed in one way or another (typically underpitched, fermentation temperature issues, or similar stressor during fermentation). Once there, I am not sure how to rid the slurry of the problem mutant presence, though plating and culturing would be one way that comes to mind.
Improvement of the beer by the existence? I suppose it’s possible if that expression is something sought in the style (4VG, perhaps or clove character in a Hefeweizen)?
Others may have specific stressors that they seek in a style
Thanks. In our case with acute over pitching, might that cause mutation?
Note that my 8th generation of W-34/70 seemed just fine after rousing it with some fresh wort. It is now chugging away in another Euro-Lager.
Your observation is absolutely correct. Yeast cultures do in fact improve in performance up to a point. It is called adaptation. Sadly, that is selective, cropping technique, and yeast genetics dependent. I am of the firm belief if one serially crops selectively and does not over pitch, what will happen is that yeast cells not well adapted to one’s selection criteria will be winnowed out leaving those that perform well in one’s brewery.
And for what it’s worth, I have taken a lager yeast out 25 repitches with no observed off flavors or performance issues. It took a couple years and I stopped only because I feltI had satisfied myself and wanted to move onto other strains.
That’s good to know. I’ve never gone that far, simply due to fear of the unknown. Around 10 generations has been the max for me. But armed with this info, we will continue to re-pitch without being overly concerned.
My yeast has sat for about 5 months, completely dormant. And then re-pitched without any problems. I try to brew faster and re-use the yeast on a more rapid schedule.
The problem arises when you have three, four, or more yeasts in storage.
I have the following, all being harvested:
Kolsch (Wyeast)
London Ale (Wyeast)
Czech Pils (Wyeast)
W-34/70 (Saflager)
Oktoberfest (Wyeast Blend)
The only ones not working right now are the Kolsch and the Czech Pils.
Mutation is complex thing, is hard to observe with some organism and easier in others, there artificial and natural selection and genetic drift, those all can enter the count to change the yeast, but I don’t think this is really a problem in brewing, you’re using a single strain, the mutation can be for a little change of flocculation or attenuation or nothing, but the enviroment you’re creating will favor those without mutation, the select strains that the lab sell to you, you’re not change too much the enviroment, you’re give the same sugars all the time you make beer, same pH, or close, and is not adding another organism to compete with the yeast so mutation can happen but I don’t think it will afect your beer, I’m speaking this a biology, but I’m not a expert on yeast mutation or nothing like this, just give my thoughts
