Cell Counting

[fromhereon]

Hi Guys,

I've been struggling to find the answer to this one but have run out of ideas and was hoping someone might be able to point out something I've missed.

When brewing we always use the MrMalty pitching rate calculator to determine the size of our starter. However I'd like to be able to see what we're actually pitching by doing a cell count. I've been using a hemocytometer from white labs and a cell counting app I wrote to do the calculations for me. However my calculations always show I have about half as much yeast as I should. The problem is not with the calculator. I've used white labs formula and tested against an endless number of examples.


I've attached a screenshot as an example to hopefully make it a little easier to understand what I'm talking about. In the example I'm calculating for .8mil cells per mL instead of .75 and I've dilluted 1 mL of the slurry with 9 mL of water.

I figure there must be something wrong with my technique. But it seems strange that it's almost exactly half every time. I do try to push the "Growth Factor" down on MrMalty to keep the starters smaller and limit the differance in O.G. after pitching the yeast.

Sorry, I hope this question isn't too involved or specific but I'm worried I may be under pitching.

 

[WoodlandBrew]

Your math is spot on. Mr. Malty is good for an estimation if you don't have the right tools, but I would trust the cell count.

My blog has several entries about cell count estimations. My book has the information organized better and covers the topic in much more depth. (it should be published next month)

If there is a mistake I would guess that it is in calculating your dilution. For example if you forgot to account for the dilution from adding stain. ( Not that I have ever done that... )

Here is a summary of my results:
http://woodlandbrew.blogspot.com/2013/03/starter-calculators-revisited.html
(At the time I took this data Mr. Matly and Yeast Calc used essentially the same equations)

 

[fromhereon]

Thanks for the response. I'll definitely check it out. I understand MrMalty's not going to be perfect but that seems pretty far off.

 

[WoodlandBrew]

Thanks! In my experience a factor of two isn't too bad for a cell count estimation.