Thermal Analysis of Conventional and Extractive Fed-Batch Ethanol Fermentation at Different Temperatures.

Very high gravity (VHG) ethanol fermentation at low temperatures can be a way to obtain wines with high ethanol content (> 15 °GL). The production of vinasse is lower, compared to typical industrial conditions, which reduces the costs of storage and transport. However, there is greater heat generation during cell growth, resulting in an increased requirement for cooling water. One promising way to cool the vat is to use CO2 stripping, which removes heat by vaporization of the ethanol and water in the broth. Therefore, the aim of the present study was to find suitable operating conditions, considering the gas flow rate ( F CO 2 ) and the stripping start ( t start ) and stop ( t stop ) times, that could reduce the volume of water required for temperature control. Simulations of extractive fermentations at 28 and 34 °C, with must substrate concentration ( C SM ) of 300 g/L, were performed to obtain F CO 2 , t start , and t stop . Experimental validations showed water volume reductions of 66.4% (28 °C) and 67.0% (34 °C), compared to the corresponding conventional ethanol fermentations. An extractive VHG fermentation at 28 °C, with C SM =372 g/L, was carried out under the conditions obtained in the simulations. The results showed a 61.9% reduction in water volume and a total ethanol content of 15 °GL. The gas stripping technique applied to VHG fermentation at low temperature was proved to be environmentally friendly, since it reduced the volume of vinasse generated and saved water, which could reduce the number of heat exchangers and the costs associated with their maintenance. [ABSTRACT FROM AUTHOR]