A Kinetic Model for Single-Yeast Sour Beer Fermentation

After understanding and implementing several papers, we decided that the math model contained in [1], was ideal to adapt to describe a lactic acid fermentation. The key aspect of the model is a switch function, which we replicated to demonstrate the change in metabolism when a sour yeast ceases to produce lactic acid during a fermentation. This model is also limited to glucose as the sugar source. Utilizing the existing rate equations and stoichiometric coefficients within the model, we were able to construct a rate expression for lactic acid and integrate it into the model proposed [1].

These rate equations should model a lactic acid production coinciding with cell mass growth causing an early pH decrease to about 3.2. We accomplished this through the switch function model approach [1] controlling lactic acid production with a single parameter which we established by comparing our model to data [1]. Our final pH was achieved at around 5 hours.

We hope that our model could be used in the industrial production of sour alcohol. Improvements include describing more realistic worts, such as maltose and maltotriose, as well as modeling a greater range of beverage production settings, as described in [2]. Fermentation modeling can be implemented to improve the ease of production and decrease the waste involved in experimentation.

[1] González-Hernández, Y.; Michiels, E.; Perré, P. A Comprehensive Mechanistic Yeast Model Able to Switch Metabolism According to Growth Conditions. Fermentation 2022, 8, 710. https://doi.org/10.3390/fermentation8120710

[2] J. Gee DA, Ramirez WF. Optimal temperature control for batch beer fermentation. Biotechnol Bioeng. 1988 Feb 20;31(3):224-34. doi: 10.1002/bit.260310308. PMID: 18584597.