Yeast Still Freezes w/ Glycerin

[troglodytes]

So, I've been meaning to ask this for a while because I'm little confused about my frozen yeast bank. Does anyone's yeast still freeze (as in ice formed solid) even with glycerin?

I use small 8 dram vials with about 20% yeast, 10% glycerin and the rest sterilized water. What appears to happen is the glycerin separates into its own layer and then the remaining water and yeast freeze. This doesn't seem right, but it has happened every single time I've done this.

I store the yeast for about 3-6 months before using again and it has always come back but I have to step up from a real small starters.

 

[erikpete18]

I'm sure somewhere online there's probably a table that lists what temp certain glycerol concentrations will freeze, but from the sound of it if the glycerol is separating out you aren't mixing out well enough. You'll definitely want to shake the tube well to get everything into solution, because otherwise the glycerol will sink to the bottom.

If you are getting them mixed up and they're not separating, freezing isn't the worst thing do long as they stay frozen and aren't going through freeze/thaw cycles. You could increase the amount of glycerin to prevent freezing, or make sure the tubes are covered in your freezer so the don't thaw during frost-free cycles.

 

[capt82]

I'm just starting off freezing yeast and have not yet used my frozen yeast. I read an article saying to remove all water from the yeast before adding glycerin. Maybe the water is causing ice crystals to form in the yeast layer?

I am testing a vial without glycerin and I removed all water from vial as well. Does not look like any ice crystals have formed in that vial.


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