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Old 07-03-2013, 04:41 PM   #1
mikescooling
 
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Hey guys, I'm trying to freeze some yeast. I've read a lot of stuff about % of Glycerin and I'm confused. I made a mix of 75% H20 with 25% Glycerin, for the purpose of keeping this simple so I can understand lets call this the "mix" I added 50% mix to 50% crashed yeast slurry (we all know how to do starters and crash). How far off am I from doing this correctly? Please microbiologist keep words small, so this pipe fitter can understand.

 
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Old 07-03-2013, 08:51 PM   #2
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Personally I think you're reversed in your ratio. Just FYI, my mix ratios are all by volume, not by weight - for me it's easier to measure a cup, vs. getting out a scale and weighing. I've done some at 50-50 and they work OK, but it took some effort to get good yeast activity after the thaw. My 75% glycerin with 25% water with the yeast slurry added (which has some additional water) has produced faster responding yeast after thawing.
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Old 07-04-2013, 12:11 PM   #3
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Back when I was in lab, we had a stock solution of 30% glycerol: 70% water and made a 50:50 mixture of yeast slurry to glycerol solution. In other words, the final glycerol concentration was 15%.

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Old 07-04-2013, 01:20 PM   #4
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One thing I noticed with the frozen yeast I have (%50 slurry %50 glycerol) is that the particles of yeast would settle to the bottom eventually. This means that unless agitated the very bottom of the tube is gonna be 98% yeast.

 
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Old 07-04-2013, 01:53 PM   #5
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Thanks for the responses guys, to recap we have 70% glycerol, 30%glycerol and 100% glycerol, mixed with slurry. You can see how I am confused? Are their that many ways to do this? What's the down side of one way working better than another? Is a larger size vial better via more yeast?
I did notice everything settled to the bottom.

 
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Old 07-04-2013, 05:53 PM   #6
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It's a fairly new technique. I used 5ml vials and all my yeast are dead in 2 years.

Might I ask your goals? And also how much storage space you have and at what temperatures you plan on keeping the yeast. I would probably just try to sway you towards keeping yeast in the fridge instead of the freezer regardless of your answers.

 
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Old 07-04-2013, 07:02 PM   #7
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Grathan, my goal is to only pay for yeast once a year. I'd like to take new yeast and make a big starter, then store that new yeast in vials in my big chest freezer I think it's a -20F, so I have lots of space. The vials I am using now are glass 25ml, but I ordered some bigger sterile plastic vials that are 50ml; I was thinking bigger is better? Are you referring to slanting yeast and keeping it in the fridge? I have room in there too.

 
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Old 07-05-2013, 11:59 AM   #8
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No not slanting, just washing. I would think it would last a year either way (freezing or fridge), though you will probably have to revive the yeast after a year. Bigger is better. My 5ml vials never had a chance. I didn't autoclave everything, just simply spray with starsan.

If I didn't have a LHBS I would try it again with bigger vials. But since I have every yeast I could need stored by local shop it just comes down to cost savings. For me it's cheapest just to reuse the yeast for all the recipes that use it and then move on and just buy a vial again down the road.

 
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Old 07-05-2013, 12:11 PM   #9
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This article here suggests %10 glycerol total and by the looks of the frozen vial, there is no settling.
http://www.homebrewtalk.com/entries/freezing-yeast.html

Here is the method I am more excited about. You just rob the starter each time you brew with a yeast.
http://www.homebrewtalk.com/entries/...-approach.html

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Old 07-05-2013, 01:00 PM   #10
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You want your total volume of slurry to contain 10% glycerol/glycerin. My technique is to make a 2L starter, decant off the wort when its finished, then add 100% glycerol so it comprises 10% of the volume that remains. You can still do the same thing with diluted mixes of glycerol, you just need to do some calculations so the end result is 10%.

It is obviously easier with graduated flasks. Make sure it is mixed very well (glycerol is very viscous) then freeze as cold as you can get it.
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