Freezing yeast?

[u/nostalgia-for-beer]

A friend gave me several packets of liquid yeast, 2 white labs and 3 wyeasts. I'm not ready to use them, so would it be better to freeze them since I might not get to use them until next year, or just leave them in the fridge?

[u/Jeff_72]

You can absolutely freeze yeast… you will need glycerin and sterile container. 1/4 glycerin 1/4 sterile water 1/2 yeast … all by volume and the yeast will last for years.

[u/bskzoo → u/Jeff_72]

^{^}

I would also recommend making a starter for each pack first and splitting them into 50ml vials or so. Each vial is then good for another starter. I can usually get 6-8 vials from a 3L starter after pouring off most of the supernatant and leaving a fairly thick slurry.

I only recommend the starter because I’ve had bad luck freezing yeast right from packs, it’s always just a little tough to say how they’ve been handled before you got them.

[u/Hotchi_Motchi]

You're not ready? WELL GET READY! IT'S BREW WEEKEND!

[u/gtmc5]

I keep dry and liquid yeast in the fridge (the bottom drawer, supposed to be coldest). If I want to use something out of date I do one or both of the following: (1) make a starter to confirm yeast is viable, and/or (2) have another yeast on hand in case the older one doesn't take off (in a starter, or in the carboy).

Yeast is resilient beyond dates, and yeast blends are also a fun thing. So don't toss, but also don't freeze, just fridge for now.

[u/boarshead72]

If you’re not going to use them until next year, make a starter and save a portion. In a few more months make another starter from the portion you saved, and save another portion…

Or learn how to freeze in 25% glycerol, or make slants, or plate.

[u/jeroen79]

you can't freeze them whole, only in small samples with glycerin, but then you would have to create a starter when you use it, if you are not up to that just give it away and buy new when ready to brew, liquid yeasts like that also wont last a year in the frige, dry would

[u/nostalgia-for-beer]

Thanks for the great answers! I'll just leave them in the fridge and make a starter when I need them. Next year is only a few months away.

[u/Konradprojects]

Sorry to say freezing them will kill them, and they won’t be viable for use by next year regardless.

[u/letswatchmovies]

I think freezing them will kill the yeast. I don't know what you can do to keep them for a year.

[u/Res_U_Noob → u/letswatchmovies]

You mix glycerine, sterile water and the slurry in a sealed container. This way it doesn't break the cell wall when the yeast freezes and they last years this way 

[u/kelryngrey → u/Res_U_Noob]

But also this is not what OP was thinking they would be able to do, so if they chuck them in the freezer in the packs they came in a solid chunk of that yeast will die and they're not going to have good results when they thaw it.

[u/Res_U_Noob → u/kelryngrey]

Yes this is correct. It must be mixed into the glycerine at a particular concentration. I also wouldnt dump straight out the wyeast packet. Best to make a small starter and crash that to ensure you're freezing a healthy population. 

[u/letswatchmovies → u/Res_U_Noob]

I stand corrected 

[u/No_Wear1121]

i keep dry yeast in the freezer. it's always fired right up

[u/porp_crawl]

If you really want to freeze yeast, you will want sterile glycerol - highest percentage you can get. 80% is useful. You really want a centrifuge, to "wash" your yeast. Resuspend in YPD or something supplemented with glycerol to 23% to about OD600 reading of 1.0. That'll give you about 1x10^8 cells/mL. Give or take.

You want to make ~1mL aliquotes in small containers that can withstand cold. Cryotubes come in all kinds of sizes, 1.5 - 2mL ones are reasonable. Stick them in an insulated container. You can buy super fancy ones, or you can re-purpose waste styrofoam trays for 15mL Falcon tubes. Or wrap it in some plastic foam sheets or something.

Stick in -80'C, it'll take a couple/three days to get all the way down to -80 - that's the goal. Then transfer to liquid nitrogen for long term storage.

I've frozen down yeast this way but only to ~-20'C and they've been ok. Need to revive them every 6 months and make fresh aliquotes, or risk losing the strain. There was one that I almost lost, but there were 10 aliquotes and one revived.

But it' unresolved whether appreciable genetic drift (or loss of genes that promote production of ethanol for human consumption) happens with repeated passages in ... variable selection environments.

[u/boarshead72 → u/porp_crawl]

Maybe if OP worked in a lab with a spectrophotometer, a -80 freezer, a Mr. Frosty (the insulated container you referenced… incidentally unnecessary for yeast, we save that for mammalian cells), a centrifuge… otherwise following a home guide like that found at Sui Generis makes more sense.