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Viability of harvested yeast

babychef

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I am considering harvesting the yeast from my current brew for the first time.  I wonder how you would recommend using it. In particular, my questions are:

1. How much of the recovered yeast would you use for a 5 gal batch of ale? How about for a lager? How about a high gravity brew?

2. How would you adjust these pitch rates if you didn't use the yeast for some period of time? After how many months would you pitch more? At which point would the viable cells be low enough that you would make a starter, and pitch all of it?

Thanks.
 
I used sterilized water to dilute the remaining beer in my fermenter and after swirling up the trub vigorously I allow the carboy to sit for 20 to 40 minutes for the trub to settle.  The liquid layer should look off white to light tan, depending upon beer color.

I pour the liquid gently into sterilized jar and seal loosely.  The jar is stored in the refrigerator until use.

The yeast cake should look creamy to white with a fine texture.  I usually figure that a clean yeast cake is around 4 to 5 billion cells per ml (I am typing this from memory and if I am off, I will correct it later).  Most slurries contain some bits of trub and dead cells, so I reduce the concentration by that percentage.

If I am pitching within a week or so, I will use the yeast calculator to determine the number of cells needed and divide that by the 'good' yeast concentration I think I have collected to calculate how much of it to pitch.

If it will be more than two weeks, I will make a starter with about half the projected amount that I would need to keep the cells active and healthy.

I always aimed high on amount to pitch and was conservative on yeast cells in the slurry versus trub.  Some amount of over pitch will not hurt in the least. 

These days, I do cell counts using a microscope to verify number of cells per ml and pitch according to that.
 
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