Determination of Ethanol in Beers Using a Flatbed Scanner and Automated Digital Image Analysis

Abstract

A new, simple, and low-cost method is proposed to determine ethanol content in beer samples. The method is economical and environmentally friendly because it uses low-cost materials based on natural indicators and generates only 200 μL of waste per test. The method is based in the reaction of ethanol with potassium dichromate in acid media generating Cr3+; 100 μL of K2Cr2O7 0.2 mol L−1 in sulfuric acid 20%, v/v was placed in wells of a 96-micro-well plate, then, 50 μL of samples or standards were placed in each well, after 1 h incubation at 60 °C, a digital image of the plate was obtained using a flatbed scanner, and RGB values were extracted automatically from all wells in less than 5 min using ImageJ’s plugin “ReadPlate.” The standard calibration plot was linear for an ethanol content ranging from 0.4 to 2%, with limits of detection and quantification of 0.09% and 0.27%, respectively. Ethanol content determined in beer samples with proposed method agree with those obtained with the microplate reader and with those claimed in labels. Thus, this method can be especially advantageous for countries were available resources for analytical equipment investments are scant.