Yeast harvesting question

I've been reading the forums on the subject of starters and the related topic of harvesting yeast for subsequent batches. I understand the issue of not going beyond five or so generations from the fresh yeast. So here's a question. Does anyone ever take the original yeast package, run a starter, immediately divide the result into, say five portions, fridge four and continue ramping the fifth up to pitching density. This way all the samples are only one generation from the original.

I'm not sure that would buy you much. Say you start with a smack pack that produces 100 billion cells. You run a 2L starter and end up with 200 billion cells. Then you divide it up into 5 batches, each one is 40 billion cells.

Now, when you want to brew an ale, you'd have to run one of those portions through 2 more starters (to 80 billion, then 160 billion) just to get enough yeast to properly ferment a moderate gravity ale. Add at least one more step if you're doing a lager. So your yeast is now 3-5 generations old already, when you finally put it to work fermenting an actual wort. If you wash it, you might be able to safely get one more batch out of it, but you could've done that anyway if you'd just stuck with the original starter and used the whole thing. Actually, you could probably wash it and use it a couple of times, meaning you'd actually get MORE fermentations out of it if you DON'T split it.

I just did a 2-step starter and oversized to pull 500mL and save for another batch. Needed 280B for my batch so figured how large I had to go in order to pull off 500mL and stll have 280B left.

kombat said:

I'm not sure that would buy you much. Say you start with a smack pack that produces 100 billion cells. You run a 2L starter and end up with 200 billion cells. Then you divide it up into 5 batches, each one is 40 billion cells.

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I'm curious, where are you getting that a 2L starter will only double the initial cell count? From Mr. Malty it says it would at least triple or quadruple the cell count.

Jayhem said:

I'm curious, where are you getting that a 2L starter will only double the initial cell count? From Mr. Malty it says it would at least triple or quadruple the cell count.

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"Research varies, but a starter of 1 quart (or liter) will yield approximately 150 billion cells, and a two quart (or liter) starter will yield from 200-240 billion cells."
-- "Home Brewing with BeerSmith," Bradley J. Smith

So I figured if I start with a smack pack (100 billion cells) and brew a 2L starter, I'll end up with 200-240 billion cells (a doubling). If I then decant off the spent wort and do it again, they'll double again. If I'm doing it wrong, I welcome a correction!

EDIT: This article in BYO is even more pessimistic:

Yeast in a starter will grow to roughly 50 million cells per milliliter of wort or 1.5 billion per ounce of wort no matter what the starting number of cells. [...] A 500 ml starter will grow to: 500 x 50 million = 25 billion.

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So a 2L starter would only produce 100 billion cells - which is what I started with in the smack pack in the first place.

Brew365 says:

As another general principle, a 2-liter starter will approximately double your yeast count

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They cite Jamil Zainasheff's article in the March/April 2007 issue of Zymurgy, "The Secret to Healthy Yeast: Making a Starter."

The answers seem to be all over the map! If yeast pitching rates are so vital, how do you guys reconcile all the wildly conflicting "math?"

When I buy a new strain of yeast I make a starter larger than needed for that brew. I then make 4) 20ml vials to freeze. I take 5ml yeast, 5ml glycerin and 10ml water. I cool them in the refrigerator for a day then freeze. I have to plan a week ahead to make a step up starter to use the frozen yeast. I have banked 7 varieties so far and have used about 5 vials that were stored for up to 7 months.

If I made up 4 more vials from each one that I used for 4 generations I could brew 256 batches from the original purchase.

Thanks for the great responses. A lot to play with. I might try to compare the effort and results for kh54's method vs just saving yeast from the primary each time.

Is there a simple visual way to assess cell quantity from the volume of the settled yeast cream?