May as well throw my novice approach into the mix as well
-50 ml non-sterile centrifugal plastic tubes boiled for 5 minutes and left in water until moments before they're filled
-Using well washed yeast (minimal trub); clean looking yeast; decanted prior to mixing
-80% glycerin solution for mixing with yeast; mixed and boiled in microwave for 1 minute; covered and cooled
-Each tube gets 31 ml washed yeast and 14 ml glycerin solution for 25% glycerin content; mixed well
-Refrigerated overnight 12-24 hours
-Given one last gentle mixing and moved to upright frosting freezer for storage
I've chosen the glycerin content based some things I read in the following blog:
Here's the real catch though..... I haven't used any yet
so I can't really comment on how well they've stored or how long they'll take to revive.
I've estimated anywhere from 60-120 billion yeast cells based on how well the yeast was washed and how compact the yeast layer. The better the wash and the more compact the layer, the higher I estimate (S-04 is a good example). I think I'm usually sitting in the 80-100 billion cell range so I basically look at it like I'll be starting with a white labs vial prior to use. This gives me the opportunity to make up a starter and build up the cell population prior to use AS WELL AS see how long it takes to revive.