Saflager 23
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maxashton
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hoppingMad
Its not any different really to Fly guys' procedure. I bought a small glass beaker in which the vials ( plastic test tubes) sit when inside the autoclave ( pressure cooker) . Plus a 5 ml pippette, some glycerine, some alcohol and the test tubes.maxashton wrote:I'd be really interested to see your procedure next time you do it.
I already owned a suitable cooler ( chilly bin) and the required ice packs.
My procedure was to step up the propagator smack pack to ensure enough dense yeast slurry for 10 tubes, each with around 5 mls of slurry inside. I decided to do this because I was not sure how much available slurry there would be inside the smack pack.
This was simply a one litre starter which after fermenting, I chilled down and poured off most of the spent wort.
Placed glycerine to the 15 % level inside each of the 10 test tubes, placed the screw caps on and stood them inside the beaker which went inside the presuure cooker, with about 3 cms of water inside. The beaker also had a couple of cm of water inside to keep it from floating and tipping over.
I had already done a "dry run" on all this so I knew the tubes/glycerine would be fine.
Bought the pressure cooker up to heat and boiled for 20 mins.
Sanitised the bench top and work area with a solution of household bleach, wore rubber gloves which I sanitised in metabisulphite and went to work with the cooled tubes.
Sterilised the pippette with alcohol, left it to evaporate and pippetted 5mls of the thickest slurry into each of the 10 test tubes containing the sterilised glycerine. This raised the contents level inside each tube to around the 50-70 % mark. It does'nt seem to matter as long as there is room to shake.
Replaced the sterile caps after filling each one and stood them up inside the same beaker untill I had finished the lot.
Shook them all up well for 10 seconds, labelled them all with strain, date etc and placed them in the fridge.
I read that yeast cell viability would be improved after thawing if the vials are stored at 2-4 degrees C for 48 hours before freezing. I can find the link for this if anyone wants to read this. But I have no way to evaluate this theory without a microscope ( and a degree in microbiology) So I just took the information for granted and did what they said.
After the required 48 hours in the fridge I decided not to re-shake them. And placed the 10 vials with a rubber band around them into my small plastic cooler box in which I had already placed a pre-frozen a freezer pack. This is to ensure the cycle of my frost free freezer would not actually have time to thaw and re-freeze my precious yeast every time it went into its frost free cycle. At this point they actually went into the freezer, which apparently is minus 18c.
The next day was when I discovered that the glycerine treated yeast slurry does not actually freeze solid but remains a viscous liquid.
Job done.
I waited a week and a half before waking up my first sample for a trial.
Placed the vial inside the fridge for the day, meanwhile made a small 200 ml starter and cooled it. Removed the vial from the fridge and left it in the kitchen to raise to room temp before pitching into the cooled wort, then pitched the yeast.
Placed the innoculated flask of wort onto my stir plate and at 21 degrees C left it there for 36 hours, after which there was no sign of life
However I knew I was asking a lot of a thimbleful of yeast in such a short time and so after 48 hours the wort was cloudy. The next day I tasted the spent wort and could detect no sweetness, indicating it had fully fermented.
Another starter wort of one litre was prepared and poured on top. This time it was all over pretty quickly after 8-10 hours on the stir plate. Next, another 2 litre starter wort was prepared, cooled and pitched and the next day had completely fermented out. I decided that I had enough yeast to pitch into a 26 litre batch of medium strength ale. So I tasted the spent wort once again to satisfy myself there was no infection.
If I were doing a lager and therefore using a lager yeast strain, I would at this point prepare a further 2 litre starter ( at least) to increase the pitching rate accordingly. ( Please note: this is my estimate of available slurry, you should do your own calculations as to how many steps are required for your own beer)
I understand that yeast slurries can be re-used over and over several times, with up to four times recommended as safe. ( debatable no doubt) So with a little planning of brewing sessions, one shoyuld be able to get up to 35 -40 batches from each Propagator pack, which for me equates to less than a dollar for yeast. Trading yeast strains with fellow brewers is also something I hope will happen occasionally, but where I live AG brewers are thin on the ground.
As you can see, I'm no scientist but have a useful stock of yeast available for some time to come.
Once again, credit to FlyGuy for this info and here again is his link where you can see all this with great photos.http://www.homebrewtalk.com/f13/guide-m ... ank-35891/
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maxashton
