I tried following the homebrewtalk how-to article on freezing some yeast last night, but when I checked it today, the glyercin solution had separated from the yeast in the freezer while freezing it overnight. Therefore, not sure if the glycerin did much or even any good. Does the separation matter? Is this what happens to everybody? Or do I need to somehow flash freeze it whiie the yeast and glycerin solution are still mixed up?
How to keep yeast and glycerin solution from separating during the freeze
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I haven't frozen yeast yet, but am getting close to doing it now. Too many strains to keep alive, and too much space taken up by them.
From what I've read the faster you can freeze them the better. That may prevent the separation you're experiencing, similar to making Eisbock.
I also read to remix them (shake?) midway, before they freeze semi-solid fro the long run. Keeping them in a styrofoam box with some ice packs or so prevents or reduces temp fluctuations, mainly when the auto defroster kicks in.
My chest freezer gets down to -4F in the bottom, but never defrosts unless I do it manually. My kitchen freezer (side by side) can go -18F, but is kept at -4F. It cycles to -18F while making ice cubes and clicks into its defrost cycle from time to time. Its evaporator is independent from the fridge side which has its own, so that's a plus for keeping more constant temps in both sides.
I'm leaning toward using the kitchen freezer for the initial freeze, then once frozen, move to a styrofoam box stuffed with ice packs in the bottom of the chest freezer.
What size vials are you using? My wife has plastic 5 ml centrifuge vials, they seem a little small, but could work. Smaller volumes, faster freezing.
From what I've read the faster you can freeze them the better. That may prevent the separation you're experiencing, similar to making Eisbock.
I also read to remix them (shake?) midway, before they freeze semi-solid fro the long run. Keeping them in a styrofoam box with some ice packs or so prevents or reduces temp fluctuations, mainly when the auto defroster kicks in.
My chest freezer gets down to -4F in the bottom, but never defrosts unless I do it manually. My kitchen freezer (side by side) can go -18F, but is kept at -4F. It cycles to -18F while making ice cubes and clicks into its defrost cycle from time to time. Its evaporator is independent from the fridge side which has its own, so that's a plus for keeping more constant temps in both sides.
I'm leaning toward using the kitchen freezer for the initial freeze, then once frozen, move to a styrofoam box stuffed with ice packs in the bottom of the chest freezer.
What size vials are you using? My wife has plastic 5 ml centrifuge vials, they seem a little small, but could work. Smaller volumes, faster freezing.
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NeverDie
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I've tried 15ml and will be migrating to 2ml: https://www.homebrewtalk.com/forum/threads/best-sealed-vials-for-freezing-yeast.662240/#post-8526780
ESBrewer
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I don't know about the effects of flocculation at this stage but I think it is not detrimental. The yeast got some time in glycerol and should be ready to be freezed no matter where it is located. In one study, cooling rate of 7°C/min (slow at lab, fast at homebrew conditions) was optimum for viability when cooling in absence of glycerol. Rapid thawing was very important, most likely to prevent reformation of crystals to larger units, although faster cooling rates could be fine with glycerol and adaptation time in cool glycerol may alter the results as well. It is a rather complex issue. Typical -15..20C is not optimum but can be used for some time. A tube too large may warm up at suboptimal rate when thawing and cooling rate and unwanted temp fluctuation(esp. freeze-thaw cycles of modern freezers) in smaller tubes can be controlled with insulation. So I encourage u to try smaller tubes and hints in say, this practical presentation:
https://www.google.fi/url?sa=t&sour...FjACegQIARAB&usg=AOvVaw0PTUEZhl5ShY6qewVhPTfN
And remember that after all, yeast can survive in a wide variety of conditions, unlike mammalian cells. So even if something goes slightly wrong, u are likely to see at least some viable (although stressed) cells that can be grown when starting on small volumes/on plate.
https://www.google.fi/url?sa=t&sour...FjACegQIARAB&usg=AOvVaw0PTUEZhl5ShY6qewVhPTfN
And remember that after all, yeast can survive in a wide variety of conditions, unlike mammalian cells. So even if something goes slightly wrong, u are likely to see at least some viable (although stressed) cells that can be grown when starting on small volumes/on plate.
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NeverDie
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Yes, I was able to recently both freeze and later revive a yeast sample, even though most of the glycerin had separated. I subsequently put it through a multi-step starter and then, this morning, I pitched it. Only time will tell how it fares.
Wow, 2 ml is a tiny amount.
I saw that thread, but sadly, those 500 vials aren't $30 anymore, they're closer to $200 now. You got yourself a real deal there!
I think I can get the centrifuge tubes in 2 or 3 ml instead. Is filling them close to the brim essential?
Using mineral oil instead of glycerine got me a little confused, That oil is going to be showing up in the starters, and thus in the beer. How are you going to get rid of it?
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NeverDie
Well-Known Member
Maybe the price will come back. Meanwhile, though, if you go looking, you'll find similar deals on similar tubes.
If you read the rest of the thread, it was decided not to use mineral oil.
The yield was pretty low when I unfroze the yeast. Next time I'll try chilling it more slowly and warming it more slowly. I may try letting the yeast steep in the glycerin for longer. Unfortunately, the exact details on what others have done is a bit sketchy.
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I've had very good experiences so far freezing yeast in glycerin solution and reviving it. Been doing this for about 2 years now.
I freeze it in a 10-11 % glycerin solution (=final concentration, after the yeast slurry has been added).
In contrast to what IslandLizard said, I mostly read that slow freezing and fast thawing is best.
Flash-freezing in liquid nitrogen would probably be the best option, but most of us don't have liquid N2 around the house, I guess...
So I'll keep the vials in an alcoholic solution during freezing to slow down the freezing rate. From what I read above, that might be overkill??
Then, I also take out the vials every 20 minutes or so and shake them, to keep the yeast as evenly mixed with the solution as possible. As stated above, this is probably overkill as well, but anyway, I feel better knowing my yeast is thoroughly mixed
with the glycerin.
After that, at around 10% glycerin, the samples would freeze solid.
During storage, I keep them in a small box filled with an alcoholic solution (=old, cheap booze) to prevent temp fluctuations
as much as possible.
I freeze it in a 10-11 % glycerin solution (=final concentration, after the yeast slurry has been added).
In contrast to what IslandLizard said, I mostly read that slow freezing and fast thawing is best.
Flash-freezing in liquid nitrogen would probably be the best option, but most of us don't have liquid N2 around the house, I guess...
So I'll keep the vials in an alcoholic solution during freezing to slow down the freezing rate. From what I read above, that might be overkill??
Then, I also take out the vials every 20 minutes or so and shake them, to keep the yeast as evenly mixed with the solution as possible. As stated above, this is probably overkill as well, but anyway, I feel better knowing my yeast is thoroughly mixed
with the glycerin.
After that, at around 10% glycerin, the samples would freeze solid.
During storage, I keep them in a small box filled with an alcoholic solution (=old, cheap booze) to prevent temp fluctuations
as much as possible.
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