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Determining viability of harvested yeast

All the yeast calculators out there that I’ve found only take into consideration density and volume. If I have yeast I harvested 3 months ago as opposed to a few weeks, shouldn’t that make a considerable difference in amount of slurry to pitch? Is there an easy way to determine viability of your slurry or some simple “rule of thumb” that you guys use to do so?

Honestly, determining the amount of slurry to pitch in general is kind of a crap shoot. Its all guesswork. In your case, I would make a starter with a couple tablespoons of slurry. 3 months, in my opinion, is pushing it.

You can store yeast for quite awhile (I have used yeast I harvested up to 8 months previously), but as mentioned above, making a starter is a good idea if the yeast is not really fresh.

Have you direct pitched 8 month old slurry?

So you think direct pitching a pint of extra dense 3 month old lager yeast slurry would be risky?

Look over these calculators and the information that goes with them. Viability % of yeast is based on date of manufacture. I estimate 1 billion cells per ml of clean harvested yeast slurry that has had time to compact. Mrmalty estimates 2 billion per ml.

http://www.brewersfriend.com/yeast-pitc ... alculator/ http://www.mrmalty.com/yeast-tools.php

I personally would prefer a starter with three month old slurry. You’ll have plenty of viable cells and it would likely work out fine for you. Not saying its risky, just not my preference.

I personally would prefer a starter with three month old slurry. You’ll have plenty of viable cells and it would likely work out fine for you. Not saying its risky, just not my preference.[/quote]

It would have to be a pretty humongous starter to accommodate that much yeast wouldn’t it?

I personally would prefer a starter with three month old slurry. You’ll have plenty of viable cells and it would likely work out fine for you. Not saying its risky, just not my preference.[/quote]

It would have to be a pretty humongous starter to accommodate that much yeast wouldn’t it?[/quote]
Use only a couple tablespoons of your slurry in the starter.

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