Dried Yeast Cell Count

[DrPaulsen]

I'd always been under the impression that dried yeast contains 20B cells/gm and that one of the principal advantages of using it was the opportunity to get very large pitching rates without making a starter. It was my understanding that a single 11gm packet of dried yeast should contain just over 200B cells, whereas a vial of White Labs yeast only contains 100B cells. This further meant that dried yeast presented a nice opportunity for cost savings (lower price, more yeast).

A note in the Brewer's Friend January release pointed me to a couple of data points that indicate the actual cell count is much lower than 20B cells/gm. Fermentis indicates 6B cells/gm for US-05 and S-04, while Danstar indicates 5B cells/gm for Nottingham. I found a presentation from Boulevard that indicates they assume 7B cells/gm when using dried yeast for bottle conditioning (I have the PDF, if you're interested, but the link is too ridiculously long to post here).

http://www.fermentis.com/wp-content/upl ... A_US05.pdf
http://www.fermentis.com/wp-content/upl ... FA_S04.pdf
http://www.danstaryeast.com/products/no ... -ale-yeast

As an example, if I run a typical IPA through a pitching rate calculator (6 gal, 1.065 OG, 1M cells/mL/Plato), using 6B cells/gm, it indicates I would need just over 5 of the 11 gm packets to reach an optimum pitching rate of 361M cells.

http://www.brewersfriend.com/yeast-pitc ... alculator/

If these numbers are to be believed, dry yeast does not present itself as a cost saving opportunity relative to liquid yeast. Furthermore, following the 20B cells/gm number creates a serious opportunity for under-pitching. Personally, I've had mixed results using dried yeast and, when I've had bad results, they very much mirrored the problems I've seen from underpitching with liquid yeast (fusel alcohols, acetaldehyde, etc.). Given that I very carefully control and measure aeration levels and fermentation temperature (which, if uncontrolled, can produce similar effects), this has never before made sense to me.

I haven't seen any research contradicting the shelf-life advantage over liquid yeast, so I suppose it still has that going for it.

[Steven P]

Activity loss is 25% per year refrigerated for unopened Notty. That's good to know. They recommend rehydration as well.

1g per liter of wort provides 5-10 million cells of active yeast. A 5 gal 1.050 beer would take slightly less than 2 packs right?

[DrPaulsen]

It depends on what you assume for the cell density and the pitching rate you want. If you shoot for 0.75 g/mL/Plato, you will need 176B total cells for 5 gallons of 1.050 wort. Assuming 6B cells/gm, this is 29 gms of dried yeast, which is about 3 of the 11 gm packets.