Simulation of the mashing process: Dissertation

Mathematical models of biochemical processes during mashing were developed: the hydrolysis of starch in all-malt mashings and mashings with adjuncts, the hydrolysis of proteins, and the effects of three microbial b glucanases on the hydrolysis of b glucans. The models for the hydrolysis of starch predict the concentrations of fermentable sugars, dextrins, and starch and the activities of a- and b-amylase enzymes during mashing. The model for the hydrolysis of proteins predicts the concentrations of free amino nitrogen and soluble nitrogen. The models describing the effects of microbial b glucanases predict the activity of b glucanase and concentration of b glucans. Measurements from laboratory scale mashing experiments were used for model identification and parameter estimation. Model predictions were compared with measurements from independent laboratory scale mashings. Industrial scale mashing experiments in two breweries were also performed. The confidence limits for the predictions of the models for the hydrolysis of starch and proteins were obtained by Monte Carlo and bootstrapping methods. The models predicted the activities of a- and b-amylase and the concentrations of fermentable sugars and FAN in the produced wort with the accuracy enabled by the accuracy of the measurements used in the model development. For concentration of soluble nitrogen, the model predictions were not as accurate as permitted by the measurements. In the laboratory mashings, the errors between the measured and predicted final fermentable sugar concentrations varied from +0.6% to -9.9%. In the industrial scale experiments, the corresponding prediction errors were +4.6%...-2.6%. For the final concentrations of free amino nitrogen (FAN) the prediction errors of the model were +10%...-6% and for soluble nitrogen concentration +2%...-8%. The models predicted correctly the direction of small changes in wort quality due to crop change in almost all cases analyzed. The models were incorporated into a simulation program called SIMA that can be used for the planning of the mashing program in brewery conditions. With the program it is possible to simulate all the major reactions taking place during mashing: dissolution and hydrolysis of starch, b-glucans and proteins. Also, the effects of the addition of barley starch and microbial b glucanases can be simulated.