What's the big deal with freezing yeast?

[TSMill]

Hey guys,

I notice there is currently a lot of interest in storing yeast by frezzing it in a water/glycerine mixture. Not wanting to shit on anyone's parade, but just wondering why this approach is preferred over storing yeast in the fridge under water only?

Flicking through my copy of "Yeast", p 188 suggests yeast can be stored under sterile water for years without refrigeration. Technically I guess my water is not sterile (I boil the shit out of it), but that is somewhat balanced out by the fact my samples remain refrigerated. Table 6.5 suggests a maximum shelf life of 3-5 years, with a reliable shelf life of 6 months (which I guess is largely driven by your individaul yeast washing and sanitation regime). I've had no issues with yeast, either washed or split fresh from a smack pack stored in this manner, and I've regularly fermented with samples brought out of dormancy that are in the region of 18 months to 2 years old.

The section on freezing (p.199) to me suggests there are many more factors impacting the viability of the end product, including how quickly the sample cools, glycerine to water ratio, temperature of the freezer etc. In addition, it notes that you should not re-freeze after a thaw, which leaves your entire library vulnerable to an extended power outage.

Anyways, not trying to start any arguments, just would like to hear some of the percieved benefits of freezing over water storage.

 

[Yob]

I plan to embed mine in ice 'trays' so will be somewhat insulated against extended power outages. Mine being in a deep freezer are pretty safe regardless.

Fridge samples I've noticed start to change colour after a month or so indicating mortality and or mutation.

Freezing slows the metabolism to essentially stopped so samples remain more true.

I've also got a copy of the yeast book (naturally) and have read up on t he other types of storage, mineral oil etc but freezing seemed to be the best long term option.

 

[mxd]

I'm just starting to freeze as yob's doing it

 

[TSMill]

Yes I have noticed some colour change, moreso in the earlier samples I stored which I think had too much yeast in the vial (although I'm not sure why that would cause an issue). Other samples show a slight darkening, but I've not noted any perceptable flavour shift in the yeast profile. Even if there were a small degree of mutation in the fridge, surely this is no more than the mutation which would occur over the course of a ferment, or building up a sample prior to storage?

 

[DJ_L3ThAL]

Ah so more water above is better than maximum yeast in the vial!? I'll inspect my yeast bank for colour differences of similar aged yeasts when I get home! Subscribed!

 

[Yob]

Ah so more water above is better than maximum yeast in the vial!? I'll inspect my yeast bank for colour differences of similar aged yeasts when I get home! Subscribed!

actually, I believe less is better, even better still is to have a layer of mineral oil on the top as this stops any air contamination.

 

[TSMill]

Meaning less yeast as opposed to less water I assume.

 

[Yob]

Erm.. No? Less water.

I also forgot to add as to why, I've got +100 frozen vials I think, about 25 strains, I couldn't do that with jars of slurry

 

[TSMill]

I don't store jars I've got the small screw top vials, probably 5-10% yeast and the rest water.

I figure a certain mortality rate is expected, having a high water to cell ratio limits the concentration of dead cell crap that the remaining healthy cells are exposed to.

 

[Yob]

But it's compact yeah?

 

[MartinOC]

Healthy debate, healthy yeast.....

 

[TSMill]

Yes, that is compacted.

 

[Yob]

well.. as far as I remember, yeast dies pretty much from the top down.. regardless of the amount of water above them. Its the oxygen getting to them and them trying to do something to adapt to the environment,

another point to consider is that while not 'put to sleep' yeast will use up it's glycogen and thehalose reserves, then that runs out... bye bye..

Its another factor that got me into freezing rather than other forms of storage.

 

[Camo6]

I'm just getting into this yeast freezing caper both for the fun of it and to have a reliable source of yeast close at hand.

I used to farm yeast in test tubes with sterile water and found some were quite usable up to a year and a half in the fridge. This was pushing the limits though and didn't always lead to a successful ferment. I found some samples started to develop a rubbery vegemite smell (from autolysis I expect) after about a year or so and this made me look into better practices. Keen to see the results from freezing.

Speaking of which, pushed the BB to it's limits last week with an ESB using a 1.5l starter of 6 month old Wy1469. Was busier than a stomal therapist, refreshing the blow off bottle repeatedly but now have a healthy sample of top cropped West Yorkshire for freezing and repitching. What a yeast!

 

[Yob]

:icon_drool2:

I know who I'll be hittin up for a vial then :icon_drunk:

 

[Yob]

I do sincerely say laughing.. I too have pulled some pretty manky looking jars out of the fridge and made great beer from the yeast.. Rinsing and pitching...

-_- .... oh them were the days when I had time to nerd right out :lol:

but as you say Camo, its fun as well

 

[Camo6]

Too true Jesse.
I've not been brewing much the last 6 months and have realised how important proper labeling of yeast is. Got jars of god knows what in the fridge but can't bring myself to chuck em.

 

[Yob]

Yeah baby, second sign of being a yeast hoarder

 

[TSMill]

OK, so having a trawl through the yeast freezing thread, various other threads on other websites, and another read through of the yeast book and this is where I have landed:

Based on the experience of this site, evidence for the viability of freezing yeast maxes out at around 12 months. That is not to say that survivability is not longer, however there is just not the evidence to demonstrate it yet. I suspect that once frozen, yeast survivability will be longer than for other storage methods, but this has to be balanced against any mortality rates which occur during the initial freeze and the thaw (mortality rates unknown).

In comparison, there is evidence that yeast stored under water is good for ~ 18 months, however most are not comfortable using it beyond this, as there is evidence of a high mortality rate, namely darkening of the yeast and in some cases a smell indicating some autolysis has occurred. A proportion of autolysed yeast should not be a problem if the stepped up quantity is significantly larger than the stored volume, provided some yeast survives.

There is a suggestion that any yeast that is not completely dormant will be subjected to mutation over time. This may be a factor if you are only ever using first generation yeast from the packet, split into smaller quantities, however I am convinced that a greater rate of mutation will occur for any process that involves either washing yeast, or propagation on a stir plate, so for my processes mutation seems a moot point.

So all of this really leaves me still sitting on the fence as to which is a better approach. Given both fridge and freezer space are ample, next time I am storing yeast I will freeze a couple of tubes and refrigerate a couple and will do a comparative test of viability after say 2 years and 5 years in storage. Stay tuned for an update in 2017.

 

[Yob]

+5 years is the number I've read.

With +25 strains now banked.. I certainly hope this is correct..

In saying that, there is a fair variation in the glycerine content in those, ranging from %15 to %50..

Only time will tell