Dry Yeast Pitch Amount

Since I came to homebrewing 6 months ago with around 20 years of microbiology experience under my belt, I have always been attentive to the type of yeast and how may cells I am pitching to my various brews–leading me to my issue with a great deal of information (incorrect as far as I can tell) floating around the web and even in some highly regarded publications–namely that dry yeast contains around 18 to 20 billion cells/gram-so a typical 11.5 gram packet from Llaamand or Fermentis would contain on the order of 200 billion cells–there does not seem to be any basis for this number and I am curious as to why it has worked its way into brewing lore.

From any commercial information I can find online dry yeast contains from 5 to 7 billion living yeast cells/gram–Nottingham 5, Windsor 7, S04 6, S05 5, BRY-97 5–meaning on the order of 55 to 80 billion viable cells/gram.

Given that best practices call for pitching on the order of around 34 billion cells/gallon of 1.048 (12P) ale wort–this would mean 3 to 4 dry yeast packages for a typical 5.5 gallon batch of ale–not the 1 pack that is so often recommended in the brewing literature–and even quite a bit more than the manufacturers recommendations of 1 gram/liter.

I know a one dry yeast pack pitch works since I have done it a few times–but I have also had some slow starts at this rate (I am meticulous about rehydrating and temperature btw). I also wonder if the flavor of the beer would be improved with a higher pitch.

I like dry yeast for its convenience and long storage and have been satisfied with the beers I make from it. I am wondering if some of the bad rep that dry yeast has comes from underpitching.

Most of all, I am wondering how the 200 billion cells/packet, 1 pack/batch information arose.

In the fermentors: Brook Trout Stout, Meadow Mouse Farmhouse Ale, Parson’s Pond Pale Ale–In the bottle: precious little :cry:

Well you blew my mind. Just looked on the fermentis webpage and S-05 has 6*10^9 cells per gram… I can’t believe I haven’t heard of this discrepancy before. I’m very curious what people have to say about this.

At least one source saying 20 billion/gm. is mrmalty.com…bold is added by me…

"Most dry yeast has an average cell density of 20 billion cells per gram. "

" (Recently there have been other numbers mentioned for cells/gram of dry yeast and folks have asked me why I believe there are 20 billion cells. I’ve actually done cell counts on dry yeast and they’re always 20 billion per gram +/- less than a billion. Dr. Clayton Cone has also stated that there are 20 billion per gram, and other folks I trust tell me that 20 billion is correct. Until I see something different, practical experience tells me this number is correct.)"

[quote=“Denny”]At least one source saying 20 billion/gm. is mrmalty.com…bold is added by me…

"Most dry yeast has an average cell density of 20 billion cells per gram. "

" (Recently there have been other numbers mentioned for cells/gram of dry yeast and folks have asked me why I believe there are 20 billion cells. I’ve actually done cell counts on dry yeast and they’re always 20 billion per gram +/- less than a billion. Dr. Clayton Cone has also stated that there are 20 billion per gram, and other folks I trust tell me that 20 billion is correct. Until I see something different, practical experience tells me this number is correct.)"[/quote]

whew… the OP got me worried. Thanks denny!

Still not being satisfied, I went and did some counting on my own–differences in data of this magnitude bug me, and by chance, I found this link implying that both answers are correct:

http://www.danstaryeast.com/articles/ce ... d-glycogen

The answer seems to be that if you count the cells in rehydrated dry yeast, you come up with a figure around 20 billion cells/gram. However if you dilute that same yeast and plate it on microbiological growth media, you will find a figure much more in line with the 5 to 7 billion “viable” /gram reported by the manufacturer–technically this figure is not for cells, but for “colony forming units” and a colony forming unit can be one cell, two cells, or even more depending on how much the yeast is clumping–meaning, as it states in the link above that, the actual number of viable cells is probably significantly higher.

How much higher is the question–is it 1, 2, or even the 3 to 4 x higher that you would need to get to the 20 billion/gram number? I don’t think data to answer that question is available.

In the end, the real question is the beer and I would be interested in hearing if anyone has done any comparisons between pitching 1 vs 2 packs of dry yeast to a typical 5 gallon batch of beer (two packs is close to the manufacturers recommendations).