Calculator Confusion/Curiosity

Ingredients
1

I only use Wyeast Smack Packs and I always make starters and have been ever since I got into this hobby. I have always used Yeastcalc for my calculations and have noticed the last several times that there are now two stir plate calculators- one is Jamil’s and the other is Troester and they calculate differently. So out of curiosity I also visited MrMalty and used the slider to make the growth factor the same as the two represented on Yeast calc and am looking for some continuity and not finding it. I’m hoping someone can give me an explanation as to where the differences are coming from.

Example:
Package date: 3/13/2013
Viability: Yeastcalc-81%, Mr. Malty 69%
Batch size: 6.25g
Og: 1.054
YeastCalc
Stir Plate: Jamil-growth factor 2.01 requires 244B cells, 1.5L starter
Stir Plate: Troester-growth factor 2.6, 292B cells, 1.5 L starter
MrMalty:
Stir Plate: 236B cells, 1L starter-sliding of growth factor made no changes

I realize, on average the difference in cells is not huge and all of my beer as attenuated well with no issues and I have always used Yeastcalc as I like the ability to calculate stepped starters so easily and I am not losing sleep over this but my curiosity has been peaked so my inquiring mind wants to know if one is more accurate than another and why the differences?

2

I can’t claim to be an expert on this matter, but it seems to me that each of the different yeast growth models is just that: a model that intends to predict yeast behavior.  My guess is that there are so many variables involved that all of the models can be considered to be correct within their respective margins of error.

I’ve settled on Kai’s since it’s the only one that shows some of the data that it is based on.  You can read about it here: Estimating yeast growth | Braukaiser.

I also found this web site interesting since it compares different models: http://www.yeastcalc.com/growthcharts.html

3

Bumping this since I’m interested in more discussion on the differences.  And hoping maybe Kai will chime in.

4

Ironically. Shortly after I posted this I found a conversion on this exact subject on HBT under the yeast/fermentation forum titled Yeastcalc-now there are 2 stir plates…

Kai has offered up quite a bit as well as Woodland Brewer with a LOT of interesting information