Yeast Viability

[philosofool]

I'm not buying yeast viability calculators. Maybe these work for harvested yeast that will be repitched, but I don't buy them for production yeasts.

Why not?

First, it doesn't fit with lived experience. I now use starters all the time, but when I started out brewing, I regularly just pitched a vial of White Labs into the wort. I once did this with a vial over four months old after making a .5 L starter with it. Nevertheless, I always had successful, if slightly slow, fermentations.

Second, if Wyeast and White Labs products were really below 10% viability after four months, there is no way in hell they would be giving a "Best By" date four months after production.

Does anyone disagree with this? Does anyone know of a better viability calculator?

 

[FredTheNuke]

Same as in my experience. The calculators are WAY too conservative / extreme. Folks have to remember that yeast have survived for millions of years.... 3 months in a refrigerator isn't gonna wipe them out.

 

[rupert130]

I personally assume a 5% viability loss per month. This is based on conversations with a local yeast bank.

 

[FredTheNuke]

that makes more sense. 6 months would be a 70% viable yeast product - fits more what I have saw when using. It does take longer for a starter to get up and running when it's 6 months old but it DOES get up and running and produce a pure clean active yeast slurry to pitch into my tasty BEERZ!