I am making a 15 gal batch of Kolsch using WY2565. My pack was a few months old and Mr. Malty calculated it to be around 25% viability. I made a 500 ml starter at 1.040 and put it on the stir plate. I let it ferment out for a couple days, activity was slow but evident. After I figured it was just about done, I added another 1500 ml of 1.040 starter and it took off like crazy (did not decant, just added more).
I cold crashed it for several days and decanted the very clear beer off the top today. I would estimate that there was 100 ml or so of yeast, not really sure how to tell since my flask isn't graduated that low. I added another 1000ml of 1.040 wort and fermentation went wild, huge thick krausen in less than an hour even though it's on the stir plate. There is probably 3 inches of krausen.
But, here is my question. Do you think that there is enough yeast there to do 15 gals? I have only used Mr. Malty but I really wish that there was a stepping up calculator that would let you work up to the amount you need from a limited number of vials/packs. I can either do one more decant and add more wort or if there is enough it can go right in.