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Two Batch Starter from Harvest

I want to do two (5) gallon batches with harvested yeast. They were harvested in February. I’m trying to figure out:
(1) How much yeast do I have in my container; on harvest date and today.
(2) What is the growth rate of yeast? Will 1L of 1.040 wort double my yeast?
(3) Could I pitch the entire harvest into 4L of wort and have enough yeast to ferment a 1.065 batch and a 1.075 batch.

I’ve never really thought about the numbers before. Usually I was pitching harvested yeast within a month and only 1/3 of a cake. I’ve made a few starters for yeast over 6 months old knowing that I’d have plenty of yeast to ferment a batch.

My goal is to accurately predict yeast counts ensuring that I properly pitch enough yeast.

Thanks all.

:cheers:

Michael,

did you look at the mr malty calculator and input your slurry amount/harvest date? i think it does a reasonable job of predicting the amount of viable yeast.

bob

[quote=“StormyBrew”]Michael,

did you look at the mr malty calculator and input your slurry amount/harvest date? i think it does a reasonable job of predicting the amount of viable yeast.

bob[/quote]
Bob,
I did, but I don’t have graduated jars so I don’t know how much slurry I actually have. I also was hoping to wrap my head around the science behind yeast production, viability, and yeast health as it pertains to beer.

If I can assume that a yeast cake on harvest date has 900B cells, then I think I can get pretty close to the amount of yeast to pitch. But if I start off wrong, everything after will be wrong also. Know what I mean?

:cheers:

Check out this page.

http://seanterrill.com/2010/03/23/yeast ... g-and-you/

Sean does a good job explaining exactly what you want to do.

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