I have 3 mason jars of propagated or harvested yeast in my kegging refrigerator. I turned the temperature down because I was getting ready to cool down a couple of kegs prior to force carbonation. After 24 hours I noticed the yeast I was storing in the same refrigerator had frozen in the mason jars. The jars were not full of liquid and did not crack. I took them out of the frig for several hours and let them slowly warm up to 50 or 60 degrees and put them back into a warmer refrigerator.
My question is did I kill the yeast in the frozen liquid? Was allowing the yeast to slowly warm to 50 or 60 degrees and putting back into the refrigerator an acceptable process? In case it matters, all yeast strains were for ales. Scotch ale yeast, high tappist? and a harvested yeast from a brown ale I recently made.
Thanks for any all replies.
You surely killed some. It’s unlikely that all of them were killed though - I’ve seen estimates of 20 to 50% loss from freezing. It’s really not as bad as you would think. Warming it up to room temperature and refrigerating them again didn’t do anything to help the survivors, but I bet it’ll be fine. Definitely make a starter before you use the yeast, though, to verify that there are living cells in there and to bump up the cell count to make up for what was killed. If yeast couldn’t survive freezing, though, they wouldn’t survive very long in nature. Some of the best spontaneous fermentations I’ve had were from when there was a couple feet of snow on the ground and the temperatures were in the upper 20’s.
Well, thanks. that is somewhat reassuring. I will make a starter the next time I use one these strains.
Do make yer starter of lower gravity so some of the viable yeast left can rehabilitate themselves and be able to bud/multiply. As the water book may suggest, in the neighborhood of 1.030-ish. Sneezles61
