[Philbrew]

So divide 200B by 16

Lost on this.  Is this the "4 doublings"?  Also, the aforementioned pitch rate 7B/L, where does it come from?  I am just interested.  I really think homebrewers in general are way overthinking yeast.

I TOTALLY agree that many homebrewers tend to overthink pretty much everything, myself included when it comes to certain stuff.  Yeast was never something I thought a whole lot about but am starting to now.

Yes, exactly.  2 to the 4th power is 16.

I got the 7B/L thing from the following link, but I'm sure they got it from someplace else.  Interwebs are probably chock full of crazy talk about billions of yeast cells and yadda-yadda and honestly I'm not even all that terribly interested in any details except for the bottom line.  And the bottom line is, I only need to use 1/4 packet of dry yeast for 5 gallons from now on, or its equivalent for my 1/3 size batches (1.7 gallons) so I guess that's 1/12 packet!  I've always used 1/4 to 1/2 packet so I guess I was really overpitching.  Anyway, here's that link:

www.northernbrewer.com/documentation/YeastPitchingRates.pdf

What has me confused is that the dry yeast makers all say their packets contain > approx. 55B cells.  That's about the same or less than a smack-pak of liquid yeast.  Does that mean that everyone is overpitching liquid yeast too?  Or is the ">" really ">>>" ?

[dmtaylor]

What has me confused is that the dry yeast makers all say their packets contain > approx. 55B cells.  That's about the same or less than a smack-pak of liquid yeast.  Does that mean that everyone is overpitching liquid yeast too?  Or is the ">" really ">>>" ?

Yes, the > is actually >>>.  When folks run real life experiments, they find that fresh packets actually usually contain 100-200B viable cells, so the >55B is super conservative, and probably applies only when skipping rehydration as so many of us do (myself included) or keeping that packet in your fridge for a up to a year or two before use (which I also do).

So, if I skip rehydration as I still plan to do always, and continue to use old yeast from time to time as I'm sure I'll also do, then maybe that 1/3 to 1/2 pack per 1.7 gallons is still the right amount for me and my little batches, and not 1/12 as I might otherwise only need to use for a rehydrated brand new pack.  etc. etc. etc.

[narcout]

I think you've accidentally squared the math.  For a standard beer of about 1.055 OG, you want 7B cells/liter, so in 21L (5 gal), that's ~150B cells/5 gal, or let's say 200B like you had.  Not 4200B!!!!  So divide 200B by 16 and you get... 12.5B, which is only a quarter of a sachet for 5 gallons!!!!

I think you are confusing the recommended initial pitch rate from the paper you linked to (1M cells per milliliter per degree Plate) with final maximum cell count (200B cells per liter).

[dmtaylor]

I think you've accidentally squared the math.  For a standard beer of about 1.055 OG, you want 7B cells/liter, so in 21L (5 gal), that's ~150B cells/5 gal, or let's say 200B like you had.  Not 4200B!!!!  So divide 200B by 16 and you get... 12.5B, which is only a quarter of a sachet for 5 gallons!!!!

I think you are confusing the recommended initial pitch rate from the paper you linked to (1M cells per milliliter per degree Plate) with final maximum cell count (200B cells per liter).

You're probably right, but 150B and 200B are in the same ballpark regardless.

[narcout]

What I mean is that you want to pitch at your target rate (whatever that may be), not be at your target rate after several replication periods.

Assuming a max cell density of 200B cells per liter, Philbrew's analysis below was correct.

If you want the beer at high kraeusen to have 200B cells/liter* in 21L, that's 4200B cells.  If you want to get there in 4 doublings (should be enough lipids for 4 replications without O2), you need to start with 262.5B cells.

[zwiller]

I am totally lost.  Somehow I was under the impression that a packet of Saflager 3470 contains 200B cells and never heard of using replication.  I don't really care.  I am successfully using it in lagers and couldn't be happer.  1 packet to 5G room temp. 

[dmtaylor]

I am totally lost.  Somehow I was under the impression that a packet of Saflager 3470 contains 200B cells and never heard of using replication.  I don't really care.  I am successfully using it in lagers and couldn't be happer.  1 packet to 5G room temp.

I'm right there with you, man.  I'll spend more time researching and doing math problems some other time.  Until then, one pack of lager yeast in 5 gallons seems good to me too, and delivers great results, so why question. 

[narcout]

Basically, you are pitching a certain number of cells into your wort (X) which then grows to a larger number of cells (Y) during the growth phase.

If you calculate Y as the max cell density per liter of wort and estimate X, there is a formula you can use to determine how many growth cycles it takes for X cells to become Y cells.

It isn’t really necessary.

More info can be found here if you are interested:  https://www.experimentalbrew.com/blogs/saccharomyces/yeast-cultures-are-nuclear-weapons

[ynotbrusum]

I, too, use 34/70 and S-189 for lagers with one sachet for a 5 gallon batch (unless extraordinarily high OG).  I once used 3 sachets on a 10 gallon batch, but then found that 1 per 5 was sufficient, so 2 in a 10er should be fine.  Highly viable product that dry yeast is.  I hope they keep expanding the strains; I want to try that ESB that just came out, too.

[Philbrew]

I am totally lost.  Somehow I was under the impression that a packet of Saflager 3470 contains 200B cells and never heard of using replication.  I don't really care.  I am successfully using it in lagers and couldn't be happer.  1 packet to 5G room temp.

Fermentis' tech specs for Saflager W-34/70 say viable cells > 6x10*9/gram.  So a 11.5 gram packet would have greater than 69B cells at minimum.  Fermentis is being very conservative with that number.  Dave's research says that the normal number of cells in a packet is, in fact, more like 200B!  So, 1 pack to 5 gal. should work fine if you aerate well and your sanitizing is good.  I pitch 1 pack of 34/70 in 5.5 gal. pils @ 1.050 and it comes out great.