So, what's the consensus on how long you can store liquid yeast before using it? Can I stock up for the year in, say, February, and let that carry me until November? Here in Alabama, we can have hot temperatures starting in March or April and lasting until late October!
Will a liquid yeast pack still be good 8-9 months after purchase? (I know, make a starter to be sure.)
White Labs'
Purepitch sleeves fare better with time than any other packaging. Only 10% degradation (loss of viability) over the first 3 months. That's only 3% per month vs. 10% per month for any other packaging. Viability declines by about 10% per month after that, pretty much as any other yeast, but you start at 90% after 3 months, instead of 70%.
I've successfully revived 3 year old yeast stored in the fridge, in original packaging, and just as successfully from saved-out starter slurries. Not saying it's the best method, making starters well before they're a year old is much easier and better.
When we receive our yeast it's usually 2-4 months old already. Sadly, that seems to be a fair average, I read that somewhere. Therefore, one should always making a starter before pitching, but more so when they're a few months old.
If you know they're not going to be used within 2-4 months after receiving, I'd make starters with those and save the crashed slurries in 4 oz or 8 oz mason/jelly jars in the fridge. The 10% decline per month clock gets reset and starts ticking down from there on. That extends their life span another 6-12 months (or longer). With good sanitation that
renewal process can be repeated quite a few times.
I had an old fashioned vial (not a Purepitch Pack) of Yeast Vault yeast sent to me from White Labs (San Diego) in March last year. There were medium hot days along the southern route it took (on a USPS truck). It was slightly warm when I received it and it took a while to make a decent starter from it.
https://www.homebrewtalk.com/threads/white-labs-wlp546-marañón-canyon-wild-cacao.662582/post-8558608