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Old 11-21-2008, 06:36 PM   #1
JoeRags
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Default Glycerin and Yeasties - is this stuff safe?

I bought CVS brand Pure Glycerin to prepare my yeasties for freezing.... Some people on the forum have said to buy the kind that is safe for ingestion, however, this stuff say's "For external use only."

Is it safe to use this stuff? I'll be freezing 20 mL of yeast solution in test tubes, so I figure 5 mL of glycerin. Is this OK?

I'm putting this stuff into my test tubes and firing up the autoclave... If I hear its no good, I guess I wont be saving any yeast from this starter...

Thanks

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Old 11-21-2008, 08:31 PM   #2
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It's fine, perfectly safe. Some yeast can eat it, not sure about brewer's/

The concentration of glycerin is good for freezing but tends to be toxic to yeast, so best practice is to freeze the cells as quickly as possible, and when thawing, warm the vial gently but quickly, a cup of lukewarm water will do this, then pitch quickly to dilute the glycerin in the wort.

Cheers

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Old 11-22-2008, 03:09 PM   #3
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Thanks... what about cooldown before the freeze? Should I put the vials in the fridge overnight to temper?

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Old 11-22-2008, 03:43 PM   #4
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Some people do that and report good results, I'm not sure those results are confirmed with a viability test, but even losing half the cells to freezing only sets you back one generation, about 3-4 hours in the case of aerobic growth.

The larger the volume you're freezing, the colder you want it to be before moving it to the freezer so it freezes up fast with small ice crystals. If it freezes slowly, then larger crystals form and this is what kills the yeast. In that case, starting the freeze at 4C rather than 24C makes sense.

I ranch my yeast in 10ml volumes, so I just put mine in my chest freezer straight off.

Hope this helps

Cheers

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Old 11-22-2008, 04:13 PM   #5
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I've had great success with DMSO is an alternative to glycerine. Picked up the DMSO at a feed store; people use it for the equine industry. I've also used a fructose sugar solution. I haven't plated any of these to determine which method maintains more viable cells but I haven't had any problems reviving cells with any of the 3 methods.

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Old 11-22-2008, 04:34 PM   #6
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Quote:
Originally Posted by Joe Camel View Post
It's fine, perfectly safe. Some yeast can eat it, not sure about brewer's/

The concentration of glycerin is good for freezing but tends to be toxic to yeast, so best practice is to freeze the cells as quickly as possible, and when thawing, warm the vial gently but quickly, a cup of lukewarm water will do this, then pitch quickly to dilute the glycerin in the wort.

Cheers
You actually want to do the opposite of that. Freezing cells slowly in glycerin (or DMSO) prevents formation of ice crystals that can lyse the cell membranes. You typically want to thaw cells rather quickly. However, there's plenty of wiggle room in there as long as you add glycercol or DMSO.

EDIT: I'm wrong here, this is for human cells, yeast you probably want to freeze quickly.
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Old 11-23-2008, 01:22 AM   #7
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Quote:
Originally Posted by Professor Frink View Post
You actually want to do the opposite of that. Freezing cells slowly in glycerin (or DMSO) prevents formation of ice crystals that can lyse the cell membranes. You typically want to thaw cells rather quickly. However, there's plenty of wiggle room in there as long as you add glycercol or DMSO.

EDIT: I'm wrong here, this is for human cells, yeast you probably want to freeze quickly.
Yep, in the lab I freeze human cells slowly by placing in an ethanol bath that is then placed in a -122°F freezer for 24 hours and then placed in liquid nitrogen which is about -196°F; the ETOH slows down the freezing. Yeast, I just freeze them quickly. For those who aren't familiar with freezers; your normal freezer in the kitchen will reach about -4 to -10°F. Someone may have plated yeasts which have been frozen to get an idea of viability; I just haven't gotten around to it. If I do I'll be certain to post the results.
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Old 11-23-2008, 03:17 AM   #8
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In our lab we would treat yeast and bacteria different from mammalian cells because of the cell walls. We would flash freeze small volumes in an ethanol/dry ice bath to get them frozen in seconds.

I wouldn't recommend storing yeast in a fridge freezer as it's not quite cold enough. If you get large ice crystals forming in your ice cream, the same process will kill your yeast in time. Best bet is a chest freezer, which is typically -18 - 20 C

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Old 11-23-2008, 01:34 PM   #9
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I thought you were supposed to use glycerol. Is glycerin the same thing? Glycerin is used to condition wine.

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Old 11-23-2008, 02:26 PM   #10
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Quote:
Originally Posted by Poobah58 View Post
I thought you were supposed to use glycerol. Is glycerin the same thing? Glycerin is used to condition wine.
It's pretty much the same thing.
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