Gowanus Brewery


Yeast Math by Jeremy
May 1, 2008, 12:00 am
Filed under: yeast

I’m trying to finish our Yeast Starter Method page, so I’m reviewing the various methods used to estimate how many yeast cells there are per unit volume yeast slurry and what volume yeast slurry you need for a given batch of beer and, oye, my head’s already spinning…

Obviously, there are simple rules you can memorize to avoid the headache of recreating the underlying calculations, but it seems worthwhile to go through the exercise at least once. I’m not sure how to organize this information, so I’m just laying out the most important relevant principles here:

Maximum yeast cell densities are not achieved until between 24 and 36 hours after pitching.

Cultures should be used immediately, or refrigerated for up to 1 week before using.

There are about 4.5 billion yeast cells in 1 milliliter of yeast solids (solids with no excess liquid).

Harvested slurry is typically in the 40% to 60% solids range.

For ales with a starting specific gravity below 1.060, pitch 6.0 million cells per milliliter wort. For starting gravities between 1.061 and 1.076, pitch 12.0 million cells per milliliter wort. For starting gravities greater than 1.077, pitch 18.0 million.

Pitch rates when using harvested slurry should be 1.5-2 times the rate of laboratory grade culture.

Most of this information comes from the Wyeast Home Brewing Technical Information Page.

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