Slurry Cell Count in X Generation?

[BandonBrewingCo]

Say I harvest slurry from Beer A which was brewed a fresh vial/sachet and say this is Xbn cells/mm.

Then I pitch that into Beer B.

Then I harvest slurry from Beer B...

Does slurry from Beer B,C,D,etc also have the same XBn cells/mm as the slurry from Beer A (all other things being equal)?

 

[rhys333]

There's a sticky at the top of this section you might want to check out. It explains what you can expect in terms of cell densities: https://www.homebrewtalk.com/showthread.php?t=579350

Basically, as long as you manage fermentation and re-pitching well, you should be able to confidently say that the slurry in the bottom of your fermentor has at least 1.5B cells/ml, and this should remain consistent from generation to generation. The longer you leave yeast slurry in storage, the more cells will die though. I like to estimate 1.5B/ml post-fermentation and ~15% cell loss per month. After 4-6 weeks in storage, I will make a starter to refresh the yeast and build up a few new cells.

I find the 15% rule works well for the first few months. After that, the yeast density seems to level off. As an example, 2 weeks ago I pulled some 3rd of 4th generation Belgian Saison slurry from the back of my fridge that was a year old. I cracked the lid and it started showing activity right away, which told me the cells were still healthy. I guessed conservatively at 50% viability and made a small 0.5L half-strength starter (1.020). It finished in a day and then I made another full strength 0.75L starter. A few days later I pitched the slurry into 6 gallons of wort and it took off like a rocket within 6 hours.