I made the samples up and let them sit in the fridge, but the yeast separated and went to the bottom after a day. So I shook it back up and put in in the freezer. Does that sound right, or should I have frozen it in the separated state?
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I made the samples up and let them sit in the fridge, but the yeast separated and went to the bottom after a day. So I shook it back up and put in in the freezer. Does that sound right, or should I have frozen it in the separated state?
You were right to shake them up. Also, if you store the vials on their side, they won't separate as much/as quickly.
I just came across this and have join the other by saying: nice write-up.
I have been building a yeast bank myself. But mostly on agar. Recently I started running into viabiliy issues with a culture that was 9 month old. It took much longer to get a pitch of yeast for a brew that I actually decided to keep at 34*F for a 2 days before I was able to pitch the yeast. I didn't want to go to the store or postpone the brew day.
Freezing yeast seems to be a nice way to make sure you always have back-up. I like to see that you can autoclave the glcerin, not sure why I never thought of that.
When I get around, I'd like to add your write-up to the Wiki unless you want to do it yourself or someone else want's to do this.
BTW, what about exchanging yeast? I have yeast on agar now and soon I should have some on glycerin.
Guess what, after shaking up the yeast into suspension, I put it in the freezer. Three days later I checked it, and it has separated again. Not quite so well defined in all tubes, but it has separated. I wonder what is going on here?
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yeah, not good when they layer out like that. You're not getting all the protection from the glycerol. Eevery freeze/thaw cycle makes them less and less viable, in case you're thinking about pulling them out, thawing them, shaking them up, and putting them back in the freezer. My recommendation is to flash-freeze them, but for those of you using glass vials you need to use your own judgement.
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yeah, not good when they layer out like that. You're not getting all the protection from the glycerol.
It is my understanding from all the micro-biologists here that the cells are not being protected by being suspended in the glycerine, but rather that the glycerol is absorbed into the cell itself. If that is correct, is seems that once the cell has absorbed the glycerol, dropping out of suspension is of little consequence to the protection process.
FWIW, my test tubes are stored vertically and have all dropped out completely. The incidence of dead (brown) versus live (beige) cells appears to have little to do with settling as some are brown over beige, others inverted, and some stratified but swirled like fudge ripple. Based only on a visual examination, I expect that the bulk of the necrosis happens well before the yeast settle out. Also, I only have two cells that are totally brown, and they were refrigerated for 1 week prior to freezing. They looked much better going into the freezer, but now look worse than many who have spent several months longer frozen.
As for freezing my test tubes, I find that about 1:10 break the glass and about 1:5 crack the plastic tops but do not break the glass.
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hmmm, I'm finding the same thing, quite a hodgepodge of final results. Some frozen and mottled, some light beige over brown, still in liquid form, with the water stratified over the top of that
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