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Topics - oly

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Yeast and Fermentation / MrMalty question: yeast harvest date?
« on: September 10, 2012, 04:26:04 PM »
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.

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I'm reading with interest the thread over in all grain, "regarding optimal mash pH ". A lot of the disussion over there is about temperature of the measurement.

I didn't want to de-rail that thread so I'll ask here: my Hanna pH meter has ATC. What does this mean in practice?  Is it supposed to mean that I can read a pH at elevated temp, say 140F, and it will correct it for what it would read at room temp? That is, if i start reading at 140F and let it sit there over time (in an ice bath) and let it drift down to room temp, that the reading should not change?

Just curious. I normally let my sample cool first so as not to confuse things, but it would be nice to know.

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