Propogating for a 40 gallon ferment...

[morrillt]

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Hey guys, any tips regarding propagating yeast for a 40 gallon ferment? I have a wyeast packet from kolch manufactured in january. Is it just a matter of stepping it up 20x? Any tips special considerations?

Mr Malty says i need 1347 billion

and my yeast pack probably has 1/2 alive, at 100 billion.

I was thinkkning of doing a 1000L starter than repitching in a 5000, multiple times until the step calculator, http://www.yeastcalculator.com/, says i am done. Am i missing something? Can i make enough yeast from 1 pack for this? and reuse into the future?

Thanks
Todd

[Tungsten]

Once you get to that big of a batch, I have no idea if or how the pitch rates and growth rates work. A couple things that jumped out at me though:

Since you're using Wyeast, 1/2 alive would be 50 billion cells, not 100.

Mr. Malty says 1347 billion cells, but that's only if you use their default for OG. If your recipe's OG is 1.047, then you're fine. Otherwise you'll need an adjustment.

When you say start with "a 1000L starter"... I'm assuming that's not what you mean. Obviously it's just a typo, but that would be 264 gallons, heh. Using the calculator at https://www.brewersfriend.com/#a_aid=5982783965026, I come up with a 2L starter (which nets about 338B cells), stepped up to a 7L starter (which nets 1344B cells). This is assuming two things: (1) you are using a stirplate and (2) you are fermenting at ale temperatures. Things change completely if you are not using a stirplate, but at these volumes, I assume you are. You would want a slightly higher cell count if you're going to ferment close to lager temps but I can't help you there.

[David_H]

I'm going to add my 2 cents worth.
This is based on work by Kai Troester (http://braukaiser.com/documents/Troester_NHC_2013_Step_Up_Your_Starter.pdf)
White and Zainasheff [Yeast] talk about growth based on initial pitch rate and starter volume, however this [in my opinion] is misleading. It's not the volume of liquid that matters it is the amount of sugar (grams of DME) that can be consumed by the yeast that are there. Troester expresses this in terms of Billion cells of growth per g of DME available (B/g). This growth rate is between 1.5-2.0 Billion per gram of wort with a solution saturation of about 2-3 B/g.

So if you pitch a starter with 1 billion cells per gram of wort you will be able to generate an additional 1 billion cells. 1B original plus 1B generated = 2B saturation.
however if you start with 0.1 billion cells per gram of wort you will reach the same saturation point of 2 billion cells but it this case you have generated 1.9 billion cells. So now instead of doubling your starter cell count you have increased by 20 times. Lower initial starter pitch rates is much more productive and efficient.

Yeast reproduce by mitosis, which means the "Mother" buds a "Daughter" and this can happen about 20 times before the Mother dies. This is essentially an 2 raised the x function, so starting with one cell at the end of 20 generations there would be 2^20 = 1,048,576 cells. And now we are just getting started. In lab controlled conditions and at pick growth rate the cell reproduction will occur on average every 90 minutes. So 1 cell to 1 Million cells only takes about 30 hours and only 7 more generations to 1 Billion cells. The only risk is possible contamination and mutation in a less than very controlled environment. But in our 1-2L flash that is a fairly low risk and in most cases we are starting with at the very least 10-20 Billion cells. So 10 B to 200B is only 3 generations

So in this case here are my calculations
40 gallons x 3785 ml/g = 151,400 ml. @ a Pitch rate of 0.75M / ml / Plato (assume P=14)
Pitch Cells = 40 x 3785 x 14 x .75M = 1590B cells (same as above)

assume a saturation rate of 2B / gram, then the total Starter needs to be based on 1590B / (2B/g) =~ 800 gm DME.

Assuming a DME : water = 1:10 (SG = 1.040) then total Starter needs to be 8 Liters.
with an original yeast count of 50 B you will need only 6 generations. 50B * (2^x) = 1590B ==> x = ln(1590/50) = 5.6 generations

You could do this in one big starter, a 2 gallon batch or 8 smaller starters. With the 8 one liter starters you would want to split your original 50B smack pac into 8 smaller batches to pitch into each starter. What you don't want to do is successively dump 1 liter into 2 liter into 4 liter etc. It only takes a very small starter pitch rate to get big yeast volumes. Remember 1 cell turned into 1 M in 20 generations, each 1 liter start will finish with about 200B cells and with a ratio of 1:1M you only need 200,000 cells to start each Starter and finish in 20 generations.

Having said all of that, this depends on good growth conditions, LOTS OF oxygen as in a stir plate with an open air cap on the flask (aluminum foil lightly folded over the top. Don't stopper and airlock. There will be so much CO2 coming off that there is almost no way to contaminate the starter and you want oxygen able to get into the Starter.

That was probable more than 2 cents, but that's about all it is worth.

============edit 2015-09-30==================
There are some math errors above in the growth rates and generations stated
The growth function is 2^x = Final Count / Initial Count
However my log math was incorrect. x = ln(Final/Initial) / ln(2)
I was missing the ln(2) which is ~0.7 so all of my generational numbers are low by a factor of 1.4 ish