Do ice crystals kill yeast?

[CodyA]

So I know the idea behind freezing fruits and such to make them softer, being that the ice crystals that form in the water actually spear through the cell walls allowing cytoplasm to run out freely. I also understand how frostbite works, where ice crystals form in the cells, breaking through their membranes, and killing them.

So my question is, does the same rule apply to yeast cells? I remember trying to keep a yeast strain for an extended period of time and thinking that freezing leese was the best way to do it. Then 2 months later, this yeast never recovered when I tried to make a starter out of it. A guy at my LHBS said it was because of the same rule that ice kills cells. I'm interested in maybe using freezing instead of pasteurization or sorbate for stabilizing a cider.

 

[diS]

Yes, AFAIK ice will damage cell membrane, so when freezing you can use glycerin solution to minimize it.
I am doing this with every yeast strain I got, I simply make bigger starter and freeze part of yeast for my bank, or freeze it after washing.

There is nice thread about his:
https://www.homebrewtalk.com/f163/d...tarter-then-why-not-farm-yeast-freeze-269488/

 

[william_shakes_beer]

and I assume the glycerine acts as an antifreeeze, lowering the freezing point of the water and preventing the formation of ice cryvstals while permitting the yeast cells to experience the cold temps. Question; do all strains or yeast respond well to freezing or are certain ones "unfreezable"? I ask because I know that not all strains are available dry because not all remain viable through the drying process.

 

[diS]

Glycerin acts as a cryoprotectant, it helps to prevent ice crystals from puncturing the cell walls.

do all strains or yeast respond well to freezing or are certain ones "unfreezable"? I ask because I know that not all strains are available dry because not all remain viable through the drying process.

This is good question, so far I had success with several strains including WLP004, WLP029, WLP300, US-05, S-04, S-33.
What I am concerned is viability, and does every strain tolerate freezing equally.

 

[william_shakes_beer]

Cryoprotectant. Hmmm. Sounds ominous. I'l have to google that one. Thanks for the response. I'm interested because I harvest and store yeast in the frige. (not freezer) I have 4 strains, up to 3 samples of each. I'm thinking keep 1 sample in the freezer to reestablish my supply should one sample become unviable due to age (12 brews per year/4 strains means one sample COULD be pitched to a starter up to 12 months after it was first havested from a split starter)

 

[CodyA]

So in theory, wouldn't freezing a 5 gallon batch of cider stabilize it so that I could add more sugar and not worry about re-starting fermentation? Since the consensus is that freezing in a water solution kills yeast.

 

[Golddiggie]

I reserved some yeast from a starter I made, used the rest of it in a batch brewed yesterday. I have another starter on my stirplate currently (for a this coming Saturday's batch) but tonight that comes off (it's the second of three steps) and I'll be making a 1L starter for what I reserved. I want to have more yeast cells to freeze for later use, which is why I'm doing the starter for the reserved yeast.

I have 1qt of glycerine (food grade) that arrived on Friday. Just curious about the amount of it to use to keep the yeast cells protected. I've read both 50% and 35% glycerine concentration. diS, what concentration do you use??

 

[diS]

I use 15% concentration.
To make it simpler I first make 60% glycerine:distilled water solution (in bigger jar so I can use it again), then I mix it with slurry in 1:4 concentration (60:4=15).

Since glycerine has different density from water, 15% (v/v) solution will be different from a 15% (w/v) solution, therefore measuring by weight is more accurate than measuring by volume.

Use this equation to calculate exact ratio:

Glycerine (ml)= (desired % x desired V (ml))/1.26
eg. for 15% solution in 500 ml solution:
(0.15 x 500)/1.26= 59 ml of glycerine in 500 ml solution

 

[helibrewer]

So in theory, wouldn't freezing a 5 gallon batch of cider stabilize it so that I could add more sugar and not worry about re-starting fermentation? Since the consensus is that freezing in a water solution kills yeast.

Just use Sorbistat K then back sweeten.

 

[william_shakes_beer]

So in theory, wouldn't freezing a 5 gallon batch of cider stabilize it so that I could add more sugar and not worry about re-starting fermentation? Since the consensus is that freezing in a water solution kills yeast.

I believe that freezing kills Many cells not All. Likely some will still survive, so there is still a potential to restart fermentation after jacking your cider.