repitching slurry calcs using Mr. Malty

[Tom R]

I've had about 300ml of 1272 yeast in a flask along with about 1300ml of beer. It's been at 34F for two months, so Mr. Malty allows for 10% viability.

Using that calculator, I need 1789ml to ferment my 10.5 gal of 1.053 ale.

But how do I get my slurry up to that volume? Decant the beer and pitch it into a 1789ml 1.038 starter? How do I know how much slurry to put in the starter?

Or is 10% too low to work with anyway, and should I just buy more yeast?

 

[RM-MN]

Mr. Malty is a pessimist. It assumes that yeast are very easy to kill and they are not. Your yeast is probably more like 80 to 90% viable.

 

[bierhaus15]

Going to play mr negative here, but I would never pitch 2 month old home brew slurry, let alone 1 month, regardless of how it was stored/collected. I know there are a lot of people here who do so and claim no off flavors, but I've counted and done viability testing on dozens of stored slurry samples from home brew and pro-brew, and slurry more than a few weeks old never produces the same results as fresh. The only exception being top yeast loaded with trehalose and stored cold under C02. Yeast companies get around this by producing yeast with little to no trub and loading the yeast with zinc and nutrients before storage. Even then, older yeast can be as low as 50% viable, depending on conditions/strain.

Assuming most bottom cropped slurry contains around 1.0 b/c/ml, you'd need around 300 ml of 100% viable yeast for that volume and gravity. Given the time/money invested, I'd just buy new yeast.