Yeast Storage

[milob40]

i have tiptoed through the minefield of threads but can't get a definate answer.
should i store my us05 and s33 yeasts in my brew fridge at 19 degrees or my keg fridge @ 3 degrees?
also i should add when i chill my water for brew day, my brew fridge is set at 15degrees so will it get angry with me for
making it colder then warmer etc.? i should point out i'm talking about dried packet type yeasts (i will try yeast farming 1 day.

 

[chrisherberte]

Check this out, by Chris White: http://www.probrewer.com/resources/library...ealthyyeast.php

 

[MHB]

With dry yeast, the optimum is about 4⁰C; the best before date (usually 2 years after manufacture) is measured at 20^oC, if cold stored the yeast will keep up to 4 times as long. So the Keg Fridge it is.

MHB

 

[Ross]

With dry yeast, the optimum is about 4⁰C; the best before date (usually 2 years after manufacture) is measured at 20^oC, if cold stored the yeast will keep up to 4 times as long. So the Keg Fridge it is.

MHB

Are you sure it's 4x Mark? - The advice given to me was a doubling of the best before date to 4 years, if stored refridgerated.

Cheers Ross

 

[MHB]

It's a half-life equation, there are lots of variables (moisture content, O₂, temperature variability, yeast strain...). Yeast are always dying and the manufacturer sets a threshold number that they regard as an acceptable pitch rate and that's going to be the use by date. Under ideal conditions the death rate will be about of what it is on a shelf at 20^oC.

Maybe I should have been a bit more expansive; a doubling of the shelf life is a very reasonable expectation in a domestic refrigerator, but under "optimum" conditions four times is what the equation shows.

Mark

 

[milob40]

It's a half-life equation, there are lots of variables (moisture content, O₂, temperature variability, yeast strain...). Yeast are always dying and the manufacturer sets a threshold number that they regard as an acceptable pitch rate and that's going to be the use by date. Under ideal conditions the death rate will be about of what it is on a shelf at 20^oC.

Maybe I should have been a bit more expansive; a doubling of the shelf life is a very reasonable expectation in a domestic refrigerator, but under "optimum" conditions four times is what the equation shows.

Mark

i have bunged it in the keg fridge , thanks again, hopefully i didn't hurt the little fellas

 

[Wolfy]

Maybe I should have been a bit more expansive; a doubling of the shelf life is a very reasonable expectation in a domestic refrigerator, but under "optimum" conditions four times is what the equation shows.

What equation?

The information posted here (Clayton Cone), and on page 160 of 'Yeast, The practical Guide to beer Fermentation' (Chris White) both suggest that when refrigerated dry yeast:
"only loses about 4 percent of its viability per year."

 

[MHB]

Oh you will either have to write your own, or pay a food consultancy an arm and leg to do it for you.

The American FDA had a model you could plug information into it was set up as "an example" of the process, can't find it anymore, looks like it has been taken down.

Start by reading something like this: - User guide to Standard 1.2.5 Date Marking of Packaged Food.
Gather all the relevant information, in this case the number of yeast required for pitching, the rate they die off at various temperatures/storage conditions, the number of viable cells in your package, make dam sure you can site references.

Then you need to do a regression calculation to work out when you think the number of viable cells is equal to the minimum "acceptable" pitch rate and you will have a time frame. Remembering you can't just use ideal conditions (i.e. 4%/year) you need to use a real world model (i.e. 20%/year) which is why the BB date on yeast is calculated at 20^oC.

Having had to do this type of calculation a couple of times, I going to suggest you then take a hunk off the calculated date, saves getting lawyers involved later, it's also a good idea to hold samples of each batch and test it periodically to make sure nothing unexpected shows up. Be warned that the requirements really do make the person who decides on the date fully responsible, cover your arse!
Mind you just looking quickly at the numbers in the link to Dr. Clayton Cone comments, if you have 64% viability at the end of 2 years, "refrigerated" the same yeast should be good for just on 10 years, I think you would need to be very careful with that number.
MHB