A Model Based Simulation of Brewing Yeast Propagation

Abstract

A comprehensive kinetic model of yeast propagation in breweries is introduced. It represents the basis for a control strategy aimed at the provision of optimal inoculum at the starting time of subsequent industrial beer fermentations. In the metabolic modelling approach presented, respiratory metabolism on sugars and ethanol and fermentative metabolism respectively, are included. Occurring limitations, due to specific nutritional data of the growth medium, were taken into account for sugar, nitrogen, ethanol and oxygen. Correspondingly, inhibitions of the metabolism by ethanol and high sugar concentrations were formulated. The model especially represents the Crabtree-effect. For model validation, literature data were used and selected experiments within the relevant range of manipulated variables (temperature, dissolved oxygen) were conducted. Model based simulations matched these data with a deviation of 5.6% and with standard deviations of 5.6% after an adaptation of three variable parameters. A relationship between the temperature and the variable parameters could be extracted, which allowed predictive simulations of the yeast propagation process using non-isothermal trajectories. It was shown, that with a precise adjustment of trajectories of both, temperature and dissolved oxygen, the crop time of the inoculum could be varied within a period of 7 to 50 h to maintain high fermentation activity for the subsequent anaerobic fermentation.

On‐line yeast propagation process monitoring and control using an intelligent automatic control system

“…An adapted metabolic model following the approach of is introduced. The model is used as a reference biomass trajectory and serves the expert system to evaluate if the process is still on track and meets the required performance.…”

“…To shift between the different metabolic states, switching points are calculated by comparing the generic kinetic equation for substrate uptake r s with critical rates dependent on substrate and oxygen concentration. A detailed description of the switching process is given in .…”

“…The reference input trajectories of substrate and biomass concentration are calculated using a metabolic growth model. Temperature dependency of the specific growth rate and substrate uptake is included using an adapted square root model proposed by Kurz et al [30,31]. The necessary process information to calculate the current states is provided by a comprehensive sensor array comprising on-line measurement of OD, operating temperature, pressure, density, dissolved oxygen, and pH value.…”

Mathematical Model of Sugar Uptake in Fermenting Yeasted Dough

“…Sugar consumption has been modeled in other yeast-fermented foods such as wine () and beer ( , ), in addition to numerous models of fermentation in synthetic medium ( − ). Several workers have quantified changes in sugar content during dough fermentation ( − ), but these data were reported on a dough basis (% w/w or g per 100 g etc.…”