Freezing Yeast

[McMullan]

Ooh erh.
You guys are worrying me! Technically I seem way out of my depth.

My experiment continues... stage 1

The wort was put on the stir plate, oxygenated, and then gently combined with my sleeping beauties now at room temp. We await ... I don't expect anything for 24hrs.

Sorry, didn't mean to scare you :lol: Honestly, the same good results are achieved by different procedures all the time. Whether flash freezing or slow freezing makes a noticeable difference in the end product, who knows? It's nice to think there is a concrete reason why we do something a certain way. It's difficult to get it completely wrong. The worst thing I ever did was forget to pitch yeast into a wort :whistle: 2-3 days later I noticed the yeast on the shelf above the FV It turned out fine...

 

[mike77]

Ooh erh.
The wort was put on the stir plate, oxygenated, and then gently combined with my sleeping beauties now at room temp. We await ... I don't expect anything for 24hrs.

Good work let us know how it goes.

 

[McMullan]

To be honest I was just planning to defrost it enough to break it loose from the vial and then dump the frozen yeast in a 1l starter like an ice cube and let it thaw and return back to room temp naturally. If there is an easy option I'll give it a go.

Checked my yeast again this evening and it seems 4 froze and 2 didn't. I only checked 1 this morning so that may have always been the case. Suspect I perhaps got a bit more glycerin in the 2 that haven't frozen.

Starter wort at about 30*C, drop in the yeast ice cube... :idea: You could do a test run with water to see how much the ice drops the water 'starter' temperature?

 

[mike77]

Ok I have just pitched one of the frozen vials into a 1L starter. I took the frozen vial and placed it in a glass of 40c water. Surprisingly it defrosted almost instantly, probably due to high glycerin content. So I just put the vial on the work top and let it warm back up again naturally then into the starter. I made a starter with some of this yeast slurry from the fridge the other day and it took off quickly. So If I didn't lose too much yeast in the freezing/thawing process I should know fairly soon if it works or not. Of course it was only down for a few days so I'll have no idea how long you can store it for like this.

 

[shuggie159]

No good news on my technique so far.
Over 24hrs and nothing.
I'll let it go another 24hrs and if still nothing I will auto clave this wort and repeat, trying another sample but de-frosting faster.
I haven't totally given up, but its not looking good.

 

[mike77]

No good news here either. 24 hrs in, dead as a dodo. Will probably give this another try with new samples from my next brew. I'll try varying levels of glycerin, 5%, 10%, 15% & 20%.

 

[shuggie159]

I'm afraid I was a bit lazy and didn't re-sanitize the wort from the failed first attempt (frozen yeast very slowly acclimatised from -17 to 20degC temp).

I just tipped in the remains of my frozen approx 15ml phial (I used approx 1/3 for first attempt) so approx 10ml straight from the freezer. Fingers crossed it looks as if it might have worked. BUT the viability of the yeast must have been very low. Had it been fresh yeast I would have expected to to roar away. Its pretty pitiful at the moment. Will report again 12 hrs time.

 

[McMullan]

No good news here either. 24 hrs in, dead as a dodo. Will probably give this another try with new samples from my next brew. I'll try varying levels of glycerin, 5%, 10%, 15% & 20%.

Vigorously mix the slurry into the glycerol solution.

 

[duncans]

I have a freezer full of the stuff, except I use fresh yeast not reclaimed.

In pressure cooker, sterilise 5 jars, around 500ml of 3:2 glycerin: water, mixed like crazy. Allow to cool before opening pressure cooker.
I take 1 vial/pack fresh yeast (approx 100bill cells).
Split between 5 small jars (I use baby food jars approx 125ml)
Top up with approx 100ml glycerin water mix, seal
Store in freezer.

When you want to use them, decant off the glycerin water while still cold. Add 50ml of 1020 DME to refresh the yeast.
Make up with a starter or 2 as per a yeast calculator, for 20 billion cells.

Using fresh yeast reduces risk of contamination IMO.
You have a better estimate of cell count too.
Using 50:50 water:glycerin isn't enough glycerin iMO. Will separate and water will freeze.

 

[shuggie159]

I confirm using my non scientific approach... just tipping-17degC yeast (mixed approx 50:50) into room temp starter, worked!
But I'm guessing there was a high attrition rate, ie many of the yeasties died. Far too much 'trub' (yeast on the bottom of the conical), than I would usually anticipate with adding this much healthy yeast.

I'm far from convinced this is yet a reliable method of freezing/rousing yeast form frozen, and judging by the level of yeast activity it would need grown-on at least 3-4 further iterations to be a pitchable size. Unless I can significantly improve on the technique it is not really viable. ie the risk and cost of culturing exceeds the cost of purchasing a new strain.

I'm going to give it another shot and see if I have better success.

 

[mike77]

Woke up this morning and bang. The starter is fermenting away pretty vigorously. I gave up on it but lazily didn't throw it away. I'll be using some new yeast on Sunday that may be worth saving so I'll give this another try.