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Home Brew Forums > Home Brewing Beer > General Techniques > Guide to Making a Frozen Yeast Bank
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Old 09-05-2012, 05:53 AM   #671
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I'm sorry if these questions were already answered at some point, but I don't have time to read all 400000 posts. I am VERY interested in anything that can contribute to the lowering of brewing costs.

1. How long can the frozen yeast be kept?Indefinitely?

2. Wouldn't you only want to take yeast right out of the pack/vial instead of from the fermenter yeast cake? Seems to me there would be hop trub and other particulate in that stuff.

3. Can you do this with rehydrated dry yeast? I realize dry yeast can keep for much longer, and is already cheaper, but free is even better.

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Old 09-05-2012, 06:41 AM   #672
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Yes that's plenty of yeast. In fact that's a lot more than I've put in. Shake them before you freeze just to be sure the glycerin is well mixed in.

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Old 09-13-2012, 06:51 PM   #673
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Thank you!

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Old 11-25-2012, 10:33 PM   #674
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This thread seems as good of a place to get answers as any, so... I plan to start freezing yeast, primarily because of the limited availability of WY3864, which I'm getting my hands on while it's around right now. I do not have a pressure cooker, however.

I plan to use sterile 50 ml conicals, so sterilizing vials is not a concern. Thus, my only concern is sterilizing my glycerol stock solution (and any equipment that will touch the yeast). There is of course no household way of sterilizing other than a pressure cooker (the efficacy of bleach solutions on surfaces/equipment is debatable), but boiling will kill anything except endospores. Tyndallization is another possible option for solutions, but is also of inconsistent efficacy (as well as being a pain in the butt).

My question is this, though. Is complete sterilization (i.e. more than what can be achieved by boiling) actually necessary for freezing yeast, given that the source of the yeast itself isn't sterile. I haven't seen anyone recommend autoclaving/pressure cooking one's Erlenmeyer and starter wort, just boiling it, in which case the starter itself will never be truly sterile and will be a far greater source of potential contamination than the glycerol/equipment.

Anyways, thoughts? Am I fine just with boiling everything, or do I really need to purchase a pressure cooker? I don't plan to passage yeast more than maybe twice, so there won't be repeated expansion of contaminants.

Thanks!

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Old 11-26-2012, 09:49 AM   #675
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If you have good sanitary brewing technique you will be fine. You're right that you will be able to use it for fewer batches. The level of contamination isn't necessarily either or for ruining a beer...you may just see a gradual degradation in flavor quality and not something that is necessarily detectable until you've reused the yeast several times.

Best practice is of course to keep everything as sterile and sanitary as possible. I sterilize my starter vessel in the oven (I use 4L wine jugs and place them in the oven at 320F for 2 hours and let it cool slowly overnight) and use precanned sterile starter wort that I prepare in batches in my pressure cooker.

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Old 11-26-2012, 10:21 AM   #676
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Quote:
Originally Posted by orangehero View Post
If you have good sanitary brewing technique you will be fine. You're right that you will be able to use it for fewer batches. The level of contamination isn't necessarily either or for ruining a beer...you may just see a gradual degradation in flavor quality and not something that is necessarily detectable until you've reused the yeast several times.

Best practice is of course to keep everything as sterile and sanitary as possible. I sterilize my starter vessel in the oven (I use 4L wine jugs and place them in the oven at 320F for 2 hours and let it cool slowly overnight) and use precanned sterile starter wort that I prepare in batches in my pressure cooker.
This is not what I need to be hearing. XD I'm a biologist by profession, so I'm already paranoid about sanitization/sterility. I guess buying a pressure cooker is unavoidable for me at this point...
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Old 01-07-2013, 04:21 AM   #677
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Let me add a data point here. I had about 20 yeast lines stored in cryotubes in 15% (v/v) glycerol and sterile water (I just removed pure colonies from a plate and put them into the water/glycerol mix). I stored the tubes at -20C in a frost freezer, and after about 18 months of this I started to notice a dropoff in viability. I couldn't get them to grow when I streaked a little bit on a plate.

Now that I'm restarting my library, I'm planning on doing 40% glycerol, in an attempt to avoid freezing (15% froze at -20).

Furthermore I'd say that a pressure cooker is an absolute necessity - things need to be sterile if you're stepping up from a small amount of yeast, there is no room for error here.

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Old 01-22-2013, 08:06 PM   #678
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Quote:
Originally Posted by passedpawn View Post
FYI, you can buy glycerin locally. I don't bank anymore (not pure yeast, anyway) but I used to get glycerin at Walmart, in the pharma aisles. I probably posted this info about 100 pages back in this thread, but thought I'd throw it out there again.
So would something like this work ?? --> http://www.walmart.com/ip/Humco-Skin...-6-oz/10417582

Also - I have been reading up and down this post regarding the glycerin and pressure cooker...

I use star-san and LD Carlson 1-step sanitizer to sanitize EVERYTHING I use... If I boil small mason jars and then star-san them afterwards (in essence doubling the sterilization for insurance pts) will this suffice to add the glycerin and yeast slurry and then freeze?

Or is it that the glycerin itself is what needs to be sterlized, hence the pressure cooker?
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Old 01-22-2013, 08:54 PM   #679
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Quote:
Originally Posted by samandbekah View Post
So would something like this work ?? --> http://www.walmart.com/ip/Humco-Skin...-6-oz/10417582
Yes, that glycerin will work. I use the Walgreen's variety. USP grade Glycerin is USP glycerin is USP glycerol...all the same (99.7%).

Quote:
Originally Posted by samandbekah View Post
I use star-san and LD Carlson 1-step sanitizer to sanitize EVERYTHING I use... If I boil small mason jars and then star-san them afterwards (in essence doubling the sterilization for insurance pts) will this suffice to add the glycerin and yeast slurry and then freeze?

Or is it that the glycerin itself is what needs to be sterlized, hence the pressure cooker?
None of these actions will sterilize. This means that, compared to using a pressure canner as an autoclave to actually sterilize, you will have higher counts of all living contaminants. This higher count will multiply and amplify at each starter step, and your results could suffer negatively as a result of the contamination.

Ex: 4-step starter from frozen vials, with either 1 contaminant or 1000:
1→2→4→8→16
vs.
1000→2000→4000→8000→16000


Pony up $100 for the presto 23qt. canner, make you yeast library properly, and then learn to make and can wort (at different ° plato) for making starters without any prep work. If you want to cook or can other things (veggies, meat, etc.) get a 3-piece regulator too.
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Old 01-23-2013, 01:35 PM   #680
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Okay but what is actually not being sanitized, the yeast or the glycerol or both etc?

And are you implying that the Star-San and 1-step cleaners are never really sanitizing the brewing equipment?

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