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Accidentally froze my liquid yeast bank

Started by BrewDorg, June 25, 2016, 06:55:51 pm

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So, earlier today I stupidly forgot to remove my little yeast bank from my freezer when cold crashing my fermenter. I set the freezer down to 1ºC, went back to check on it and saw my vials had all frozen :(

What's the deal now? I put them into room temperature water as soon as I found them and they have unfrozen since. How much damage have I done? Are all my vials unusable now?

mr hoppy


Try making a starter.

One time the kids put a vial in the freezer for a week while I was away. When I found it I put it in cold water in the fridge to defrost and it was ok. The more gently you warm it back up the better.


Hopefully the water was gentle enough. A little starter is a good idea, will have to do that to be safe. Massive pain in the arse to do a starter for each vial though :(

Leann ull

Water explodes the cells and renders them useless, you'll have to propagate one at a time to see if they've gone.
Probably turned mutant if they are still viable


I'd use them with caution. Had a similar experience and although the starters were ok there were off flavours and attenuation issues I put down to the condition of the yeast.

Leann ull

So there's your answer bin them rather that wasting 5 hours brewing and shit yeast


If they were frozen solid then not many cells will have survived. If they were still slushy there might be higher viability.

The quickest way to test them would be a batch of small starters. you wont need more than 200 ml of 1.020 wort per yeast strain.  Say you have 10 different strains in vials, boil up 2.5 l of wort, maybe throw in some yeast nutrient. sterilise 10 x 500ml bottles in the oven (15 mins at 150C and let them cool). put some squares of tin foil in the oven aswell to sterilise.  Measure roughly 200ml into another bottle and use this as guide/measure to fill the other 10 through a sterile funnel. Add a thawed yeast vial to each bottle and label each one. use a piece of sterile tin foil to cover the bottles. Treat as a normal starter from there and save whichever ones show signs of life after a day or two.

If they're readily available yeasts then thats still a lot of effort but if you have anything special then it might be worth doing.  And probably best to do a 5l sample batch with any rescued yeast just in case it has mutated, though not all mutations are a bad thing you might have accidentally created a new super strain.


There's only 1-2 strains in there that I'd be gutted to lose. I'm going to make small starters with both and hope for the best.

I had a brand new White Labs vial in there with the others and it didn't freeze at all. I assume the thicker wall on the vial prevented the contents from freezing, luckily enough. It's a lager yeast too (WLP 833), so hopefully I didn't kill many cells or that starter is going to be huuuuge.

mr hoppy

CH is correct.

The ice crystals are spikey and poke holes in the yeast. If the ice melts too quickly the yeasties insides fall out. If you melt the ice slowly (e.g. by putting the vials in cold water) the holes in the beasties seal up before their insides fall out. But definitely make a small starter first, and then a bigger one and be prepared with dry yeast... And that's if it warrants saving it. The only reason I didn't just dump the vial was that it was a Platinum. I wanted it for a specific brew and I wasn't going to be able to get another one.

Probably better to make a small starter and step it up for the 833. If you put it in a big starter right from the start it might get out competed by nasties.

I had an out of date vial of this and made a 500ml starter, decanted half and stepped up to 2l. Apparently stepping up by a factor of 10 is optimal for yeast growth.


I've decided to try to save my Vermont Ale Yeast and dump  the rest. Its not rare but €9 a pack makes it worth trying to save.

I'd planned a 2 step starter for the 833 anyway so might just do step 1 twice to ensure life and proper growth. Thanks for the advice.

Leann ull

Gutted for you but we all drop clangers from time to time, in brewing better to admit defeat and cull rather that limping on, your beer will thank you for it.


This is true, I'll know better in future. The worst thing is, I thought this might happen so I got a little 17L fridge (that johnrm on here kindly gave away) to keep my yeast in. He dropped it to my parents place in Cork and I haven't had a chance to go get it yet!