Glycerin and Yeasties - is this stuff safe?

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JoeRags

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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
 
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
 
Thanks... what about cooldown before the freeze? Should I put the vials in the fridge overnight to temper?
 
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
 
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.
 
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.
 
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.
 
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
 
In response to the OP, I have never entirely figured out the exact difference between 'ingestible' glycerine (aka glycerol) and that labelled 'for external use only'. My pharmacist emphasized the difference to me, but it might just be something as simple as an FDA approval (which is very expensive). It might also be that the production facility for food-grade glycerine has higher standards of purity and sanitary procedures. Regardless, food-grade glycerine is generally easy to find at any pharmacy or wine-making shop, so I have always just used that.

Regarding the cold-conditioning prior to freezing yeast, the purpose of that step is to stimulate the production of trehalose in the yeast cells. The presence of this sugar in the yeast cell wall has been linked to greatly enhanced survival following freezing. You can easily stimulate trehalose production in the yeast cells by storing them in the fridge (as cold as possible without freezing) for a couple of days before freezing. This suggestion was based on advice from a presentation that was given at the 2007 AHA National Homebrewers Conference by Tom Schmidlin entitled "Freeze Your Yeast! Long term storage options for your most precious strains." It is based on some very good science, which is summarized very nicely on the website of the journal "Science" here.

Here is a link to Tom's NHC presentation -- it is a good read. He discusses why you want to slow freeze your yeast, and he talks about some experiments he ran looking at freezing techniques and yeast survival.
 
USP glycerol is safe to drink, use a 30% final storage solution, put your testubes into the fridge to cool before introducing your cooled yeast.
The "frozen" yeast need to be in a non "frost free" freezer.
 
So far I have 100% success in reviving 1 year old frozen yeast, including the fragile weizen yeast.

This thread is very interesting and informant for me, it will help me improve my freezing techniqe.
So far I took just 50-50 glycerine and yeast from unsmasched Wyeast pack into 10ml vials, and put it in the freezer.
 
sorry i can't remember where I read this but I know of one man who stores his backup yeast library in distilled water. The yeast are really quite resilient. The key to this approach is to avoid introducing any contaminants when regrowing a working culture for pitching.
 
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