This work makes use of the so-called phenomenological non-structured modelling approach to propose a novel mathematical structure for the description and prediction of the pH effect over an Isopropanol-Butanol-Ethanol (IBE) fermentation system by Clostridium acetobutylicum pIPA3-Cm2, which includes both an in-line approximation of the pH of the culture medium and also novel expressions to reflect its real time effect over the biomass growth and metabolic response in an attempt to generate a base for the development of process intensification strategies for said fermentation system for biofuel production purposes. The proposed model attained a correlation index R-2 = 0.9931 and a p-value < 0.001 versus experimental data reported by Lee at al. (2012), predicting a total of 20.1617 kg m(-3) of IBEs with a yield of 0.3341 kg(IBE) kg(Sg)(-1) after 42 h of batch fermentation. Additionally, both the proposed parameters for critical and optimal pH (pH(c) = 3.4977; pH(op) = 6.5) and simulation results based on the equation proposed for the modelling of the pH dynamic were consistent with experimental reports for both ABE and IBE fermentation systems under a wide array of operational conditions.