Fed-batch ethanol fermentation at low temperature as a way to obtain highly concentrated alcoholic wines: Modeling and optimization

摘要

The effect of product inhibition on yeast hinders the production of wine with ethanol concentration above 80.0 g L-1 (similar to 10 degrees GL) in the industrial ethanol production process commonly performed at 34 degrees C. Lowering the fermentation temperature is a way to produce wines with higher ethanol contents. In this work, batch fermentations were carried out at temperatures of 28, 30, 32, and 34 degrees C, with initial substrate concentration of 180.0 g L-1, using industrial yeast under conditions reproducing those found in industry. The Andrews-Levenspiel hybrid kinetic model, considering viable cells, showed an excellent fit to the experimental data. Kinetic parameters were determined for the different temperatures. The model was used to simulate fed-batch fermentations at different temperatures, with the same total substrate concentration, resulting in satisfactory descriptions of the process behaviors. A new optimization strategy to obtain the maximum possible ethanol production, based on the C-Emax parameter of the Andrews-Levenspiel kinetic model, provided ethanol production of up to 134.7 g L-1 (17.1 degrees GL) at 28 degrees C and 305.4 g L-1 substrate. A modification was made to the Andrews-Levenspiel kinetic model, relating the n parameter to the final ethanol concentration (C-EF), in order to enable the model to describe the behavior of fed-batch fermentations performed with high substrate concentration and at temperatures from 28 to 34 degrees C.