Yeast slurry froze in fridge...

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Yooper

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Not necessarily toast.

But most likely reduced viability, due to cell rupture from getting frozen. Just make another (step) starter with it and see. Give it a few days.

Or just buy new and make a starter with that. ;)
Sorry to be so terse! It's happened to me, and even with making a starter, the yeast apparently weren't as viable as I hoped and the entire 11 gallon batch was contaminated. It's definitely a risk, but maybe it's worth taking to some.

I threw away about $50 of ingredients plus my time, so I think it's not worth taking a chance. Yeast is not cheap, but at $9/pack it's sometimes better to start over if in doubt.
 

IslandLizard

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Sorry to be so terse! It's happened to me, and even with making a starter, the yeast apparently weren't as viable as I hoped and the entire 11 gallon batch was contaminated. It's definitely a risk, but maybe it's worth taking to some.

I threw away about $50 of ingredients plus my time, so I think it's not worth taking a chance. Yeast is not cheap, but at $9/pack it's sometimes better to start over if in doubt.
Thanks for the HU!
I wholeheartedly agree, reviving a frozen slurry is not for novices or brewers who don't have much experience with making proper yeast starters and estimating cell count and growth. You can't be in a hurry either.

@Yooper, in your case, a 10 gallon pitch requires double the amount of healthy cells, that takes some work, time, and proper judgment.

If a starter doesn't grow enough healthy cells for a pitch, the batch won't ferment properly and likely spoil, stall, or taste like crap due to infections getting a foothold before the yeast can crowd them out.

In the frozen yeast scenario, 24 hours on the counter or stir plate the day before pitching won't likely cut it.

I've grown enough starters to have learned that a starter from a mishandled yeast slurry (frozen, overheated, old, improperly stored, etc.) can take a week or even longer to grow enough cells for a proper 5-10 gallon pitch.
Most often a step starter is the best or only way to get a colony with reduced viability back to proper pitching rates.
You also need to learn or know the visual signs of good cell growth before going into the next step, for maximum propagation.

Definitely use a yeast calculator and some educated, conservative guesses as to the viability of a frozen slurry and how it's propagating.
 
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Joshua Hughes

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It was a mason hat that I had already gotten 4-5 batches out of plus the batch I harvested from. I’ll pitch. Wasn’t going to use S-04 for a few batches down the road so that puts me more in doubt. I dov1-1.5 gallon batches so I didn’t lose much $

thanks!
 

IslandLizard

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It was a mason hat that I had already gotten 4-5 batches out of plus the batch I harvested from. I’ll pitch. Wasn’t going to use S-04 for a few batches down the road so that puts me more in doubt. I dov1-1.5 gallon batches so I didn’t lose much $

thanks!
Yeah, it doesn't owe you anything at this point, just one more... please...

It depends on how hard it froze too. If it was just at 32F it would probably be fine. It's when the liquid starts to freeze solid and expand where cells get damaged. Beer contains alcohol and some sugars, lowering the freezing point a few degrees.

I always make sure to have my yeast propagated and ready before brewing a batch. If the brew gets delayed for a few weeks, I make a vitality starter a few hours before the pitch.
 

DavidWood2115

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White Labs provides a yeast banking service where they cryogenically freeze yeast (-80C), so clearly yeast can be frozen and thawed successfully. I agree that there are likely to be techniques to minimize cell wall damage, but I recently thawed out a badly frozen batch of WLP-001 and restarted it with no apparently ill effects (18 hours on stir plate, 18 hours off before chilling). Brewed a batch with it on July 4th; it started up within 12 hours and is going strong now. Expect it should be fine.
 

Andre3000

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You might be ok. But Let me ask you the $1M question: Can you make a starter? Always make a starter if you can.

Looks like they brewed a beer no problem:

Straight from the horses mouth (I love Imperial):

"Please try to store your yeast at 33-35°F (~1°C). If you accidentally freeze your yeast, thaw slowly: in a refrigerator. Experience has shown that the yeast will survive the freezing and thawing, but we recommend making a starter if this happens."

Did I mention you should make a starter if you can? If you can't, make sure you have another backup plan. I hate gambling with yeast, but I do loves me a good experiment. If you had a lot of slurry, I say pitch it per the Brulosophy experiment. Good luck!
 
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