Yeast Generations

[JeffStewart]

So I'll be starting a yeast bank this weekend was wondering, after so many generations the yeast isn't the same as what you started with due to inevitable mutations. What then? Do I just buy another culture and start again? Is there a way to check for mutations early on or would I need a full blown laboratory for that? Can find anything on Google.

Thanks in advance.

 

[COLObrewer]

You can save more than one sample from your first gen. then use it to propagate from.

 

[smchasta]

you keep a proprietary strands of the yeast so you don't have to worry about the mutants after several propagations. It really shouldn't be a huge issue unless you have a strand that you really really like.

 

[giligson]

Yes, there will likely be some drift and its very dependant on your yeast species and your storage conditions. Most mutations will result in yeast that does not grow well rather than yeast that has completely different organoleptic (taste) properties. There is no hard and fast rule on this. Determining the drift in your own population of yeast requires some fairly sophisticated lab equipment. My suggestion is that you just continue subculturing and using yeast from your own bank until you hit a problem batch. That might give you a rough idea of how long you can keep this up without trouble. You may want to shedule purchase of new strains at about the time that you feel your old strains may be in trouble.

 

[erikpete18]

I wouldn't worry too much about mutations in your stocks for quite a while. A majority of mutations won't give any advantage to the yeast, so they won't take over the entire stock. The only problem I could see is if you accidentally selected for a particular trait, then you'd be supplying the selective pressure. For instance, if you only stocked the most-flocculant yeast from each successive batch, you'd eventually select for a highly flocculant yeast.

Otherwise, until a batch actually turns out bad I wouldn't worry too much. For my peace of mind I stock like COLObrewer mentioned. I freeze down 5 samples from the first gen, and then each time I grow up a sample I freeze down another 5 samples of 2nd gen., etc., etc. This way I've got a collection of first gen to go back to if need be.

 

[JeffStewart]

Ok, so I just keep freezing new samples as I grow new starters so in all actuality, it would just take forever for me use up all the samples including down to the 1st gen samples right?
Anyway to keep the samples frozen for longer than a year without affecting viability too much? Thanks again.

 

[erikpete18]

Ok, so I just keep freezing new samples as I grow new starters so in all actuality, it would just take forever for me use up all the samples including down to the 1st gen samples right?
Anyway to keep the samples frozen for longer than a year without affecting viability too much? Thanks again.

That's what I do. That way if I ever get worried about a particular yeast, I don't feel bad going back to the 1st gen stocks and tossing any newer ones I'm concerned about. I "freeze" mine in a glycerol solution (~40-50%). I say "freeze" because at freezer temps they don't actually freeze, which is what you are looking for. I also keep them in a freezer box with a few ice packs to prevent the defrosting cycles of the freezer from harming them. I haven't had to go back to any samples older than a year yet, but I might be in the next couple of weeks for a older hefeweisen strain I've got and I'll try to remember to let you know how it works!

 

[JeffStewart]

I really appreciate it! And if you can, let me know how the yeast work out.
Thanks again to both of you.

 

[Bmorebrew]

Besides all that, I recently talked with the head brewer from a local craft brewery here in Baltimore and he said their practice is to use the yeast until 15 generations.

 

[JeffStewart]

Really that long? I thought 5 was starting to push it. Of course I don't work at a brewery nor am I a microbiologist.

 

[erikpete18]

In the case of a brewery I could see taking it even longer and trying to make it a house strain. As homebrewers we normally want the strain to act like the wyeast/whitelabs description page says it should. Big breweries that use the same yeast over and over for a handful of different types of beer could try to produce a selective environment for the types of yeast they'd like to get. I'm sure that's how Pacman all got started!

 

[JeffStewart]

Ok, so now I have two more (broad) questions:

1) How would I go about producing a house strain?
2) How does Wyeast and White labs ensure purity?

 

[erikpete18]

Well if you're going to make a house strain like a brewery, you'll want to find a yeas that is already pretty close to what you are looking for (standard ale yeast like 1056 or 1028). Then brew batch after batch of beer and keeping washing yeast from each batch and pitching it into the next one. Whether or not it actually changes might be hard to tell, but at least you can call it your house strain!

Can't say for certain about whitelabs and wyeast, but they likely keep stocks of their yeast frozen and streak out a plate from those. From there they can get a colony grown up from a single yeast and check it out to make sure it is what they think it is. Plenty of aseptic technique and quality control and its pretty easy. Not sure if they do more than just take a look under a microscope to check for purity, but it would be pretty easy to run a sample to detect any contaminants (bacteria, wild yeast). I'd be curious to know if there is anything they do to tell one yeast strain apart from another. It wouldn't surprise me if they'd sequenced their yeast strains, in which case they could go back and check to make sure the yeast is correct, but I'm just taking a shot in the dark here

 

[JeffStewart]

Ok, well again. Thanks for the info.