chopper wrote:Just wondering why the rapid drop off in calculated viability for yeast slurries as compared to vials. Mr. Malty calculates a thick slurry w/ a low percentage of non-yeast particles at 60% viability when it's 3 weeks old, but 82% viability for a vial on the same production date.
I'll go back and listen to that show, but the difference between the two calculated viabilities seemed a bit large.
Cheers
Here is a quote from the White Labs FAQ that should help to answer that.
Yeast that is harvested after a brewery fermentation will typically have a viability of less then 50% after 30 days. Our high viability is due to the health of the yeast and nutrient content of our liquid at packaging.
Essentially new yeast from a vial has been in a very sterile nutrient-rich environment for the majority of its life whereas yeast from a slurry has had potential contact with any number of variable microorganisms. Not to mention yeast has had to actively work throughout the fermentation where yeast from a vial hasn't. Yeast from the vial has a better concentration of nutrients and much less genetic mutation than yeast that has been through a fermentation.
Also keep in mind these are all statistical averages. White Labs has tested a variety of breweries probably both reputable and not so reputable so this is not to say that every brewery used the best practices to properly handle yeast. So it is certainly possible to get better than 50% viability after a month but you would need to really know what you were doing for the best results. So it depends...
