Indirect measurement of the alcohol concentration during the industrial distillation of Cognac.

Distillate alcohol concentration is an important parameter in the two step distillation used to produce Cognac spirit. Consequently on line measuremen t of alcohol concentration is useful. Nevertheless the sensors currently ma rketed are not suitable, due to their lack of precision, their cost or due to volume implementation constraints. This paper reports the development or an indirect measure for industrial applications. It is based on the measur ement of two parameters 1) the temperature of the saturated distillate stea m, 2) the atmospheric pressure and also on a model relating these Values to the alcohol concentration. Two models were proposed which allowed high pre cision over the whole range of alcohol concentrations (0-80% vol.): A polyn omial model gave a good accuracy for high concentrations (from 80 to 60% vo l.) corresponding to the extraction of the "heart", whilst a recurrent neur al network was necessary for the lower range (from 60 to 2% vol.). The aver age accuracy of the measures was +/- 0.7% vol.; The method was sucessfully tested on stills of Various sizes (25 hL and 100 hL), thus demonstrating th at is can be easily implemented in other industrial applications. The indir ect evaluation of alcohol concentration reported herein, which was tested o n two industrial stills, is now being routinely used for industrial distill ation.