If I do a 2 liter starter with one vial of WL0001 or maybe a Belgian Ale yeast, can I then repitch that yeast starter (after decanting wort) into another 2 liter starter wort and double it again? Or should I pitch half the yeast starter? I know the amount of growth is limited by size of the starter vessel, I use a 2 liter Erlinmeyer flask.
If you use Jamil's calculator, a new vial (1 week old, 95% viable) in a 2L starter on a stir plate will get you 304 Billion cells. If you decant and make another 2L starter on a stir plate, his calculator shows you should get 587 Billion if you plug in 304% for viability. I do not believe this would be the case though. The inoculation rate is way to high to get that much more growth. It would probably be more like 440 Billion cells after the step-up. I made an excell spreadsheet from the data in "Yeast" where you plug in the starter size and cells pitched and it gives you the expected final cell count. The data in the book is for non-agitated starters, for stir plate starters you would expect 50% more growth.
Dry yeast is 20 Billion cells per gram. If you do not properly rehydrate dry yeast, half the cells will die after pitching.