freezing yeast slurry

[lari]

hi,
i accidentally froze some yeast slurry. discovered it a few months later. pitched it into 10ltr of wort. signs of fermentation were observed 24 hours later. 6 weeks after that I’m sipping this beer and its good. i dont understand.. i thought yeast die when frozen?

 

[bigbeergeek]

No doubt some did die! I'm impressed it made acceptable beer! Interested in more input from others.

 

[FVillatoro]

Freezing will not immediately kill yeast.
However, frozen water can puncture cell walls and that will reduce the viability.

You can even harvest and freeze-store yeast with glycerin:

https://www.homebrewtalk.com/showthread.php?t=35891

 

[Qhrumphf]

Some surely did. But when you're dealing with living organisms, not many things are a straight up "light switch" absolute. Some obviously survived, but no idea how many. Your beer obviously fermented. "Good" is subjective- perhaps there are no off-issues, or perhaps you just can't detect them, no way for me to know. Would the beer have been better had the yeast NOT been frozen? Probably so, but again no objective way for me to know.

From what I understand, it's not the actual temperature that kills the yeast, but the formation of ice crystals. There are means (glycerin is what comes to mind) of preventing that, where yeast can be stored in a deep freezer all but permanently. That way a "mother culture" of yeast can be kept and single cells taken and grown up into pitchable cultures.

In your case, enough cells escaped rupture via crystallization to survive. That's all.