Frozen Yeast Stocks?

[~MikE]

I work in a lab and we typically keep stock samples of cells (bacterial and yeast) at -80C in 10% glycerol (the 10% glycerol prevents damage to the cells when freezing). i don't have a -80C freezer but managed to freeze some us-56 slurry with 10% glycerol, i figure it mightn't be good indefinatly but it should last at least a year. anyway, i was wondering does anyone else freeze yeast as an alternative to using slants?
-mike

 

[Darren]

I work in a lab and we typically keep stock samples of cells (bacterial and yeast) at -80C in 10% glycerol (the 10% glycerol prevents damage to the cells when freezing). i don't have a -80C freezer but managed to freeze some us-56 slurry with 10% glycerol, i figure it mightn't be good indefinatly but it should last at least a year. anyway, i was wondering does anyone else freeze yeast as an alternative to using slants?
-mike

Howdy Mike,

You might find that yeast are more stable at 4 C in water than -20 C in glycerol. Most -20 C freezers these days cycle on-and-off (frost free). This cycling is detrimental to all living organisms even in glycerol.

cheers

Darren

 

[itguy1953]

I am a baker and I have just started experimenting with freezing dough with yeast in it.

First experiment on the weekend worked. I froze the dough on Saturday morning, and pulled the dough out of the freezer on Saturday at 6pm and let it thaw and prove up.

When I came into bake at 2am on Sunday morning the bread had risen to perfection, and I baked it off.

So the yeast survived a short life in the freezer as it was still alive and worked its magic in the dough. Now I will test out what effect long term freezing has on the yeast.

I assume that brewers yeast will behave similarly to bakers yeast.

Barry

 

[~MikE]

huh, cool, i would have thought that the yeast would have died...

i was reading the yeast farming thread, 12 months is fair impressive. i'm thinking if i can revive the frozen slurry i'll start washing and storing them in the freezer with the glycerol. my chest freezer isn't frost free BTW so shouldn't be too bad for stable temps.

 

[Thirsty Boy]

I freeze yeast in a glycerol solution - about 50%, but its not exact and there is no real reason I chose that ratio. They last perfectly well and I've started a few up that were frozen for more than a year.

But you need to take note of what Darren said about frost free freezers (mine isn't frost free) everytime they thaw out a little you will kill off some yeast. I have heard people talk about buffering their yeast sample against this by storing them in a small cooler with ice packs.. all inside the freezer.

Mind you, we are talking about the equivalent of a slant - nothing like a pitchable amount - I mean 5ml of yeast slurry and 5ml of glycerol. It takes a while to build it up for pitching.

Thirsty

 

[mfdes]

They'll last a while in a -20 manual defrost freezer, but not indefinetly as they do at -70 or -80. I keep my stocks at -70 at work. They're just labelled with codes so nobody else would know what they are. Why don't you do that?
Otherwise, as stated above, 4 degrees would probably last slightly longer than in a cyclic defrost freezer.
If you're going to keep them in the fridge, though, I'd slant them. It's not hard to do, though it's a pain to have to periodically subculture them. I just take them to work and use the laminar flow when nobody else is using it.

MFS.

 

[~MikE]

They'll last a while in a -20 manual defrost freezer, but not indefinetly as they do at -70 or -80. I keep my stocks at -70 at work. They're just labelled with codes so nobody else would know what they are. Why don't you do that?
Otherwise, as stated above, 4 degrees would probably last slightly longer than in a cyclic defrost freezer.
If you're going to keep them in the fridge, though, I'd slant them. It's not hard to do, though it's a pain to have to periodically subculture them. I just take them to work and use the laminar flow when nobody else is using it.

MFS.

yeah i was thinking of washing and prearing the frozen stocks at uni (few minutes work with a centrifuge, then storing in YPD media, hello long lasting yeast )

i'll definitly store some specialty and/or expensive yeasts at uni

 

[Darren]

Hey Mike,
If you work anywhere near a cell culture facility you will lose your testies if workers in this facility find you with yeast in their hoods 8(

Be warned.

cheers

darren

 

[bigfridge]

If you work anywhere near a cell culture facility you will lose your testies if workers in this facility find you with yeast in their hoods 8(

Is that what happened to you, Darren ? :lol:

 

[Darren]

Hey BF,

No my ex took mine.

I would remove testies/outer-labia from anyone I found culturing yeast in my hoods though

 

[~MikE]

Hey BF,

No my ex took mine.

I would remove testies/outer-labia from anyone I found culturing yeast in my hoods though

we do pretty much exclusively bacterial stuff in my lab, obviously i wouldn't use mamalian cell culture laminar flows

 

[bigholty]

I would remove testies/outer-labia from anyone I found culturing yeast in my hoods though

Bwaahhahhaaa!!! That's a classic quote. Is that like the scientist's equivalent of 'busting a cap in someone's ass if they be dissin' a brother in my hood' ???

 

[Darren]

Cremated I suspect

 

[domonsura]

Cremated I suspect

:lol: I thought it was more along the lines of 'keeps them in a jar on the kitchen windowsill & periodically takes them out to bash them with a hammer'......see.....I know.....I have 2 (yes 2!!!!) ex's just like this....

 

[Darren]

:lol: I thought it was more along the lines of 'keeps them in a jar on the kitchen windowsill & periodically takes them out to bash them with a hammer'......see.....I know.....I have 2 (yes 2!!!!) ex's just like this....

Hey Domonsura,

My ex uses the produce of my testies to cause me pain. I am sure yours does too.

Good info here: http://www.dadsindistress.asn.au/

EDIT: Sorry for off topic. Of course yeast survive for a couple of weeks or so at frozen temps. Long term storage at -20C will kill them as they freeze-thaw-freeze-thaw-freeze-thaw which is how frost free freezers work.

In water at 4 C is the way to go

PPS. Barry, for that time period why freeze?? Surely the fridge does what you need (stop the yeast multiplying)

 

[~MikE]

PPS. Barry, for that time period why freeze?? Surely the fridge does what you need (stop the yeast multiplying)

freezing, if done right, captures the yeast in log growth phase for long term storage (they revive better this way). typically it's -80C for indefinite storage, i'm looking at -20 for min 1-2 years so i don't have to continuously re-inocculate slants.

yeast will stop growing in the fridge, but other processes continue, and the cells do degrade over time, whereas, theoretically a frozen stock shouldn't drop in viability as long as the temperature is maintained and they're initially frozen with glycerol to prevent freezing damage.

 

[Darren]

Hi Mike,

I understand that but Barry was freezing his bread dough overnight and then using it the next day.

cheers

Darren

PS Which lab in Adelaide are you from??

 

[~MikE]

Hi Mike,

I understand that but Barry was freezing his bread dough overnight and then using it the next day.

cheers

Darren

PS Which lab in Adelaide are you from??

ahh right right

i'm at flinders uni

 

[MHB]

Ive been tinkering with this for a couple of years, the following is some information that I dug up
There are some good practical guides, #4, thats for someone far more skilled in the subject than me.
But I think its the one that might be the most useful.

MHB

View attachment 20271
View attachment 20272
View attachment Freezing_yeast_3.doc
View attachment Freezing_yeast_4.doc

 

[~MikE]

nice find MHB, #4 was exactly what i was after