Stir Plate died, help calculating growth

[Hopper5000]

So yes, my stir plate died. I made a starter last night and woke up this morning and it's not working correctly.

I am going to borrow a friends today but it probably will be absent from a plate and just sitting for 12-18 hours. I am worried it's not on the plate during one of the more peak growth points (I started it about 6pm last night).

I know if it's not on a plate the growth rate is significantly less. Any thoughts on how I should account for this? I'm not home so I can't use the intermittent shaking growth as I am not doing that method.

It's for a big beer and in a 5L flask. I was planning on going home and then maybe making 1 or 1.5L addition to it and add that in today to try to give it more sugar and make up for the time off the plate. Is that even a good idea?

Should I make it more concentrated, like 1.050 or 1.060 vs the normal 1040 to make up for the gravity from it already propagating?

 

[TheZymurgist]

Use this:

http://www.homebrewdad.com/yeast_calculator.php

Just calculate the first step as if it was never on the plate, and that will give you a conservative growth factor. Then you can play around with the size of the second step to get you to where you want to be, cell count-wise.

 

[Hopper5000]

Yeah not a bad idea but the first "step" isn't done yet. I am also technically diluting it a bit by adding more starter to one where some sugars are already gone.

I am brewing on Sunday and usually like them to site on the plate for one to two days and then cold crash at least over night, which is why I wouldn't just do an actual 2nd step

 

[WoodlandBrew]

The main difference between on and off a stir plate is the growth rate and not the yield. In a paper I read recently they showed a 20% increase from shake flask to pure anerobic respiration. A stir plate is similar to shake flask and with out the stir plate it is somewhere between the two.

The real drive of cell growth is the amount of extract consumed. You'll get about 1 billion cells for every gram of extract. That makes calculating your cell count pretty easy.

I'll dig up the paper if you want.