Freezing yeast: best glycerine/water/yeast ratio?

[EnglishAndy]

I've read all tutorials here and on the wider internet and am still a bit unsure of the best ratios to use for glycerine, water and yeast slurry.

I have the kit: 20ml autoclavable glass jars with screw tops, dropper pipette, pressure cooker.

I have yeast that I want to freeze from an overbuilt starter in a mason jar. It's quite a sticky strain so I plan to decant nearly all the spent wort off the top then shake the remainder around to make a slurry that I can suck up in the dropper.

The question is what's the best ratio of distilled water/glycerine to use for the anti-freeze solution, and then how much of that solution to use per-pot versus my yeast slurry?

Interested to hear what people have done that's resulted in yeast that's been good for a year in the freezer.

 

[paneubert]

At this point I just put 3 mL of pure glycerin in the bottom of a 15 mL tube with all the remaining (about 10 mL) space as yeast slurry. Shake the hell out of it. No "water" added at all. This works best for me. Yeast do come back from their deep sleep.

3 mL glycerin in 15 mL tube is about a 20% glycerin concentration, which works well for me.

For your 20 mL tubes, I would just eyeball between 3-5 mL glycerin.