An improved model for prediction of wort fermentation progress and total diacetyl profile

Diacetyl is normally considered to be an off-flavor in lager beer, and its removal prolongs the overall brewing process. Here, the effects of fermentation temperature (9, 12, and 15°C), initial wort pH (4.8, 5.1, and 5.3), and wort free amino nitrogen (FAN) content (222, 252, 287, and 366 ppm) on diacetyl formation and removal in lager beer fermentations were studied in order to develop an enhanced model for predicting fermentation progress (alcohol content, biomass, and pH) and diacetyl concentration. The relationships between model coefficients, temperature, pH, and FAN were calculated, and models predicted fermentation and diacetyl profiles with a good fit (overall relative mean square error less than 10.1%). The model was validated, and also applied to a larger-scale fermentation involving a different wort and yeast strain by adjusting model coefficients. The model can be used for predicting diacetyl concentrations and for brewing process parameter optimization in industrial fermentations.