Friday, May 23, 2014

Fermentation Model

For my book I developed an excel based model for yeast growth.  This was based on experimental data, physical and biological properties, and also a few "scale factors" to align the model with measured data.  Most of the data is from beers with an OG from 9°P to 16°P (1.036 to 1.064) at temperatures near 70°F (25°C) using standard pitch rates of US-05 yeast and Briess Malt extract.  The model should hold up fairly well near those operational points, but I am sure there will be some deviation in nearly every case and significant deviation in a few cases.

Description of Graph
The lines are generated by the model.  The squares and diamonds were measured experimentally.  The cells that have an orange background are intended to be changed. 

Total Sugar - Sugar concentration in degrees Plato (multiply by 4 to get brewers points)
Single Chain - Component of Total sugar that is simple sugar
Two Chain - Component of Total sugar that is more difficult to ferment 2 chain sugar.
Sugar - Measured sugar (Refractometer corrected for alcohol)
Yeast Suspended - Billions of cells per liter (as counted on a hemocytometer)
Total Yeast - Calculated total yeast population
Yeast Suspended - Calculated yeast remaining in suspension (note that this is highly strain dependent, but can be adjusted in the model)
Growth - Billions of cells grown per day.

My book goes into more detail about the application of this model and how this graph can be used to better understand yeast growth.

Yeast Growth Fermentation Model Download


  1. Stephen my name is William Looby, I would love to know more about this excel file and how to use it, you said it was explained more in your book, what is the name of it?

    1. The cells that have an orange background are intended to be changed. (I just added that to the post) There is a section on interpretation of this graph and fermentation in general is explained in length. The book is Brewing Engineering. Here is a link to it: