General Category > Yeast and Fermentation

MrMalty question: yeast harvest date?

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oly:
I'm going to be re-pitching from slurry for my next batch. The MrMalty calculator says I need ~400B cells.  The beer I'm harvesting from has been in primary, on the yeast for 55days. I'm going to pitch the slurry to the new wort the same day I 'harvest' the yeast. So the calculator says I need 200mL of slurry to get the 400B cells. But I'm just thinking, this yeast has been sitting at the bottom of primary for a long time....is that harvest date really accurate for predicting the viability?  If I just play around and say it was harvested 25 days ago, then I would need twice as much slurry.

So, I'm just trying to figure out, is the viability of the yeast slurry a function of when I harvest it? OR is it more a function of when it finished fermenting and settled out? They yield significantly different answers for required mL of slurry for re-pitching.

Kaiser:
you would have to count from the end of the active phase of primary fermentation.

55 days is a bit old and I'd take a tsp of this yeast into a starter and grow a fresh batch.

Kai

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