Doing a weekend of brewing. Started it off today making a bourbon mash. I got an ultrasonic cleaner a while back I’ve been itching to use. I’ve seen research papers showing some evidence of it speeding up the aging process and I’ve been dying to try it. Tomorrow I’m doing two experiments, brewing an imperial milk stout and doing a keg fermentation with a jumper to another keg to purge the o2 because I’m a cheap bastard. Never fermenter in a keg so I figure it’ll be a fun thing to try. Lastly, because the yeast was expensive I’m going to try to freeze back some yeast from the starter I overbuilt and use it in another brew down the line.
How do you plan to freeze the yeast?
As I tried something like it few years ago I got that consumer freezers are a bit too leathal for yeast. I stored mine in tubes on agar in fridge and it was good after 4 months, but to get to that point was ~3 weeks of work.
I plan on following this process:
https://youtu.be/uxnUrDIqN5g
My girlfriend is a research scientist and she said they basically do the same thing but with a higher percentage of glycerine for their -80 degree freezers and liquid nitrogen so it should work well in a home freezer at the 25/75% ratio. One way to find out though lol
Is the frost-free freezers that are bad due to the freeze-thaw cycles that keeps them frost-free.
I don't remember that much, I think it is something about temperature - the -80°C freezers just freeze the culture much faster so you don't kill the cells. You can mitigate it by using glycerol as antifreeze but it is bit more work.
With agar you store only the pure 1st gen of the yeasts so there is bit more work after you unfreeze them. So there is probably different method to freezing yeast cake.
When I messed with the yeast I used this playlist as instructions:
https://www.youtube.com/playlist?list=PLZ3Z2428mCTqDFK-3ZSNpZBXJfTaMtRXE
There is something about the storing of the yeasts (I think they can last years frozen).