[theDarkSide]

In about 10 days, I am going to brew a doppelbock with an OG of  about 1.085.   I just purchased 2 packets of Wyeast 2124 that I was going to make a starter with.  I have a 2L flask and a stir plate that can handle that volume (i.e. it will not run a 5L flask) and I don't have time to brew another smaller beer and repitch the yeast.

I was on yeastcalc.com and see there is a new setting that Kai had developed.  After inputting required info, it looks like I would need to step up the starter a couple times (3 2L starters to be exact, although it's a little too close to the amount...I always like a little cushion) to get to the amount of yeast I need. Funny thing is with Kai's formula, if I only use 1 pack of yeast, the end result is almost the same, about 661B cells.

Now I have time to do this, but I noticed the first starter grows the cell count to about 352B cells.  Would it be possible to get a second 2L flask and do 2 separate yeast starters and combine them on brew day for a total of 700B cells instead of trying to grow up a starter with a couple other steps? 

It would definitely save time, and give me a little more insurance that there is enough yeast available.

Thanks.

[davidgzach]

I don't see why not.  I'm having trouble with Kai's numbers versus Jamil's.  I find I'm taking the average....

Dave

[morticaixavier]

I just did that. needed lots of yeast only had three days, pitched three vials, each into it's own 650ml starter and combined at pitching time.

[Jimmy K]

I'm looking at a chart in "Yeast" showing growth achieved from different inoculation rates. The ideal pitch rate (for cell growth in starters) is 50-70 billion cells/L which means a single 100billion cell package needs a 1.5-2L starter for optimum growth.  Above that concentration and yield decreases because there are not enough resources for cells to divide.  At 100b cells/L you get 50% less growth. At 200b cells (a 1/2L starter) you get 90% less growth. Lower than ideal pitch rates will get you more cells overall, but starter efficiency sufferers. For instance, pitching 25b cells/L means your using twice as much starter but only getting 50% more growth.

So that's all a long way of saying that a multi-step 2 liter starter starting with 2 packages of yeast is not going to grow much initially, and with each step the pitch rate just gets higher, resulting in even less growth for that step. So two starters (or one 4L starter) would be ideal.