Modeling of saccharide utilization in primary beer fermentation with yeasts immobilized in calcium alginate

Immobilized beer fermentation was studied using an industrial bottom-fermen ting yeast strain Saccharomyces cerevisiae. The yeast cells were immobilize d in 2.5% calcium alginate gel and used for brewing in a five-vessel cascad e reactor. The fermentation was performed at 15 degreesC at various flow ra tes. A nonstructured mathematical model was developed to simulate the perfo rmance of continuous primary fermentation of lager beer. The model was base d on the following variables: maltose, maltotriose, glucose, fructose, etha nol, and cell concentration. Experimental values of these variables were de termined in samples taken at regular intervals.For experimental data fittin g a nonlinear regression was used. Substrate consumption was characterized by specific substrate consumption rate and saturation constant. The values of these two parameters were optimized for all four substrates. Inhibition effects of substrates and product were analyzed using various inhibition pa tterns. Only the inhibition effect of maltose on maltose consumption was cl early identified. A good-fitting relationship for maltose inhibition was fo und, and inhibition constants were calculated.