Forgive me if this has been covered elsewhere. Which yields more yeast cells, a single 4 liter starter, or 2 2liter steps with a chill and decant in between? This is assuming using a stir plate.
Tom?
That I don’t know without testing 
Theoretically it’d be the same, assuming you have sufficient O2 and the same amount of sugar. But that doesn’t mean that’s how it would turn out. I could imagine reasons for it to go either way.
Using the 4 liter starter, would there be an advantage to hitting the starter with a minute of pure O2 daily. I use 6000ml Erlenmeyer flasks with a foil cap.
Wyeast gives a distinct advantage to 2-step starters.
There was a thread on this a little while ago that discussed this (and also linked to that Wyeast calculator as well)
http://www.homebrewersassociation.org/forum/index.php?topic=2534.msg29558#msg29558
My understanding from this and other sources is that multi-step starters do produce more growth. Taking it a step farther, from the discussions and sources I’ve seen I’ve gleaned that identical volume multi-step starters will give you more yeast. So if you do a gallon starter, chill, decant and do another gallon you’ll end up with an increased cell count, the growth rate is just lower.
Is that calculator assuming 100% viability?
I must be doing it wrong, because when I use a single step 1-gallon starter with a stir plate it tells me the final concentration in that starter is 121.69 million cells per ml. When I do two steps that are each .5 gallons, it tells me it’s at 90.15 million cells per ml. Same total volume, more cells in the single step than the 2-step. Am I missing something? Also, the calculator is not decanting in between pitching, it is assuming you are adding more wort. Anyway, based on how I’m using the calculator the 2-step seems to be at a disadvantage. What am I doing wrong?
Yeah, you’re right. That’s interesting. But try doing a three step starter using a stirplate at 0.5 gallons, 1 gallon, and 1 gallon. You get 90.65 million cells/ml. If you put in a single 2.5 gallon starter you get 72.37.
It’s not a very useful practical calculator since, as you point out, it doesn’t allow for decanting. But interesting as an example. If I could find a good source for growth rate functions I think I could build a spreadsheet to approximate the cell counts.
Maybe you’re not doing anything wrong. Maybe it’s time to email Greg and ask him what’s up?
I think you’re right, there seems to be a mistake in the formula they are using. When I use a 1 gallon single step starter, the second step says 121.69 M cells/ml. If the second step adds 0.1 gallons and you add that to 5 gallons of wort the total volume is 6.1 gallons with 16.26 M cells/ml. But if instead you use 0.0001 gallons for the second step, your final volume is 6.0001 with just 0.83 M cells/ml. That can’t be right. I’ll email Greg.