Frozen yeast still viable

[ampersandrec]

I just wanted to share my recent yeast starter experience in case anyone else experiences it as well.

I harvest my yeast and store it in growlers in the fridge. About half the time I don't wash it and just pour the swirled yeast cake into a sanitized growler or bottle. In this last brew day, I put one yeast cake growler (WLP001) in the fridge and the other in the kegerator, as the fridge was out of space. What I discovered, when checking the yeast leading up to the next brew day was that the growler in the kegerator was right up against the condenser in the kegerator and was full of ice and slushy yeast. I assumed they were goners, but decided to make up a starter and see anyway. I made a batch of starter wort and pitched it in 4 bottles of yeast. They took off at the same rate, mostly, and by 36 hours they were both looking really healthy. If you can't make out the labels, the ones on the left were slushy and the ones on the right were good.

 

[Reno_eNVy]

Great post! Yup, yeast vials/packets/etc. that appear to be frozen can still have some viable cells!

Also, super cool square growlers. Where did you get them? What volume are they?

 

[ampersandrec]

Those are actually White Labs yeast bottles. Like giant, square versions of the vials we buy at LHBS. I got those from a brewery where a friend works after they're done with them.

 

[bja]

If it was still slushy, then most of the yeast didn't freeze.

 

[passedpawn]

I've accidentally frozen them solid, very solid, and still revived the yeast just fine. Just recently did this with Wyeast Kolsch yeast.

 

[jagec]

Normally you want to use a cryoprotectant like glycerol when you freeze yeast, but they are hardy little buggers, and so often quite a few of them will survive even without the cryoprotectant.