I decided a while ago that I was going to try and freeze some yeast after reading about someone else doing it with some success.
I had nothing to start with so I made a stir plate first up. A fan out of a dead computer and a voltage regulator out of an old set of cranes did the trick.
The fan has 3 speeds but is only used on the lowest setting with the voltage regulator adjusting a 12v supply. This seems to work perfectly.
I managed to pick up an erlenmeyer flask and some plastic tubes and I was off!
I bought a packet of wyeast 1056 which I grew up in a starter to get an end count of 450 billion cells (yeast calculator). After fermentation was done I cold crashed the starter and poured off the beer to leave behind 450mls including the yeast.
200mls I tipped I to a Dr Smurtos Golden Ale I had just made and the rest I distributed between 10 tubes. This should theoretically give me 25 billion cells in each tube. I probably would have been better using 5 tubes and going 50 billion cells in each, maybe next time.
After the yeast was in, I added 5mls of glycerol and 45mls of pre boiled water for an end result of a 10% glycerine solution.
Wacked those in the fridge overnight to chill down, then cracked the lids and put them in the freezer. I gave them 24 hours in the freezer and them put them inside a lunch box with a couple of frozen bricks to protect against the defrost cycle.
I gave them 1 week and then pulled one tube out and defrosted it in a cup of water. I tipped the defrosted yeast (the whole tube, 50mls) into a 1.5L starter and chucked that on the stir plate.
The next morning I had a nice krausen going and it took somewhere between 36 and 48 hours to ferment the starter out.
Once it had finished I cold crashed the starter and had a nice layer of yeast sitting on the bottom!
IF all cells survived, and IF the yeast calculator is accurate, I should have close to 200 billion cells, enough for pitching. I am tempted to save the yeast and get it counted, but honestly couldn't be bothered stuffing around. Next time I have a brew down I'll do the same process. If the brew ferments correctly then all is well, if not I will up the original yeast count.
Anyway here is a couple of photos.