Microwave dielectric spectroscopy for determination of ethanol concentration in brandy

Brandy is one of the most consumed alcoholic drinks in Mexico. A study by the National Laboratory for Consumer Protection of alcoholic drinks marketed in Mexico, priced at no more than $ 130.00 mexican pesos, found that while most of the brandy-type drinks analyzed meet the standards, some do not meet the ethanol content that they declare. For this reason, it is necessary to determine ethanol content in alcoholic drinks to assure the quality and authenticity. This is an important opportunity for microwave dielectric spectroscopy which can be a faster and cheaper technique for the determination of ethanol in alcoholic drinks that other techniques such as chromatography. In this work, the complex relative permittivity of liquid samples with different ethanol concentrations in brandy is presented. The brandy considered was Presidente
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because it complies with the Mexican Official Standard. The study covers a concentration range from 0 to 50 % v/v. The measurements are performed with an open coaxial probe in a range from 500 MHz to 20 GHz and the Havriliak-Negami model parameters are presented for the different samples. A data analysis process was performed to predict the ethanol concentration by means of these dielectric parameters. The model was created with the training set and evaluated with the testing set. The feature chosen for the model was the dielectric constant under direct current. The mean squared error resulting was 1.071 while the model found in the literature and which is based on relaxation time was 1.21. The information presented in this work could be employed for the design and implementation of microwave microstrip sensors which are able to measure ethanol content in brandy in real-time and cheaply.