Yeast Generations

[rsmith179]

Love the new brew science channel. The questions is regarding yeast generations: how are those measured exactly? In other words, I'm going to limit myself to a certain number of generations of washing/top cropping before starting over.

For all intensive purposes, would each pitch be considered one generation? I was kind of thinking that each time you feed the yeast, another generation goes by.

Example: Start with a vial of White Labs yeast (1st Generation). Pitch into starter (2nd Generation). Pitch into Primary (3rd-? Generations...).

As you can tell, I'm utterly confused regarding the "genealogy" of yeast...

 

[BarleyWater]

1st generation would be the first beer made. The vial you buy is built up by the starter and added to the primary, and all the original yeast is present, plus it's "offspring". When you wash the yeast and build up a new starter, most of that yeast is brand new and not from the original batch making it the second generation that will go to work on the second beer.

I usually get a few jars of yeast when I wash, so I have a few second generations, and then can get even more by the third generation. If you play your cards right, you could make dozens of batches of beers on only 4 or 5 generation of yeast, provided that you have used proper sanitation techniques.

 

[rsmith179]

That makes total sense... Thanks for the info.

 

[fratermus]

Check out this precis.

 

[giligson]

Check out this precis.

Thanks for the ref its very interesting. So they repitched the ale yeast 98 times and the lager 135 times and showed no genetic drift - the only reason they didn't do more was they ran out of time for the study. Of course the results only speak to making a certain type of beer with a certain strain of yeast under very stable conditions.

 

[pjj2ba]

Just to be a little nit-picky. I'm suspicious that the techniques they used weren't definitive enough to say there weren't any genetic changes. Actually, not suspicious, I do know that their techniques certainly will miss a lot of genetic changes - those would require a complete sequencing to find ($$$$ - actually getting closer to just ($$ these days). They simply saw no changes in the markers they were using.

To be technical, in the lab setting, a new generation is the time it takes for all of the yeast to divide once. In the lab, this is two hours. Different meaning of the word than from when talking about brewing. Yeast will go through many generations in a single fermentation, but a batch is also considered a generation

 

[brrman]

If a yeast still imparts the same flavor traits after 10 generations, why should I stop washing the yeast? Does it become less flocculant? I guess sanitation will determine how many generations you can go before the yeast changes?

 

[conpewter]

I always store yeast from my starter and pitch the rest of the starter into the wort. This way I never have to try to separate the yeast from the trub in the fermenter.

 

[beds]

If a yeast still imparts the same flavor traits after 10 generations, why should I stop washing the yeast? Does it become less flocculant? I guess sanitation will determine how many generations you can go before the yeast changes?

Yes! It's all a gamble! I think people with good sanitary practices give up on a strain because they are worried about ruining a day of brewing. I subscribe to the school of thought that your yeast will adapt to the beer that you are making and become better in subsequent generations. What you say about flocculation is interesting, I think. I am also of the school of thought that the yeast that is most valuable to me are the ones that stay in suspension until the end - working for a long time. I harvest my yeast from my secondary to attempt to get these marathon cells instead of the sprinters that end up in the primary. I also primary for a short time.

 

[pjj2ba]

I believe the typical British practice is to collect yeast (ale) for later batches from the top, early in the fermentations process. These are the most vigorous fermenters. Ones that have already settled are too weak (I'm talking about within 3-4 days).

By collecting yeast from the secondary, you are selecting for yeast that don't flocculate well. I don't think this neccessarily means they are better fermenters. This can lead to more difficulties in getting your beer to clear - if that matters to you.

 

[Piotr]

The biggest issue when reusing yeast is contamination. There is no way to avoid it completely while racking, washing etc - our equipment is sanitazed, not sterile.
Once the microbes are in the slurry, you can't get rid of them. And they multiply 8-10 times faster than yeast, eventually there is enough of them to spoil beer.

 

[fastricky]

The biggest issue when reusing yeast is contamination. There is no way to avoid it completely while racking, washing etc - our equipment is sanitazed, not sterile.
Once the microbes are in the slurry, you can't get rid of them. And they multiply 8-10 times faster than yeast, eventually there is enough of them to spoil beer.

I'm quite interested in this topic.

I just dumped a beer I made with a 10th re-use of a Kolsch yeast. It tasted off and infected.

Is this where acid washing yeast would come in to promote a longer life-span of yeast re-use? (Perhaps not 10, but say, 7-8?)

There's surprisingly little info on acid washing on this site... what say ye?