Maybe you should have hung onto that chest freezer mateYob said:In no way do I have a problem.... even if I am doing a major upgrade to my yeast bank
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Just a thought, this might already have been discussed in this thread but too long to back through it all - will food grade propylene glycol work as well as glycerine??
The reason I ask is the way I understand things, the yeast survive freezing temperatures because the glycerine doesn't freeze and prevents ice crystals from bursting the yeast cells.
I don't suppose it matter which one you use, both are water soluble and both can get well below freezing, I think it's -50C for PG
There are two schools of thought I've run across. One is that the glycerine keeps the yeast from freezing. The other is that the glycerine keeps the yeast from dehydrating. However, that doesn't answer the question of whether glycerine or propylene glycol. Give it a try. do yeast from the same batch, half with glycerine, half with pg. Be interesting to see how it goes.
None of us have a problem, Yob. Until we admit we have a problem all is well.In no way do I have a problem.... even if I am doing a major upgrade to my yeast bank
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Glycerol will work better than polypropylene glycol. The way glycerol works is not intuitive: it's apparently due to the very complete mixing of glycerol and water inhibiting the ability of either of them to link up, thus inhibiting crystal formation. Reference here.
Simple freezing point depression (eg propylene glycol) is a different mechanism: it's a colligative property, meaning that it depends on the quantity of solute present not on its identity. In the case of freezing point depression it works by diluting the solvent (water) thus reducing its equilibrium vapour pressure via Raoult's Law. This in turn reduces the temperature at which the vapour pressure of the liquid equals the vapour pressure of the crystal form (ice) which is the definition of freezing point.
None of us have a problem, Yob. Until we admit we have a problem all is well.
I have a question though. With a bank of that magnitude, I imagine the stock turns are relatively low. If that is the case some of your yeast must sit in the freezer for some time. Have you determined an optimum use by shelf (freezer) life? I have some that are about 10-12 months old at times and they seem to fire up OK.
See you, Anthony
How long before adding the yeast do people sterilise the tubes with the water glycerine mixture? Will a couple days/week be alright?
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