Versatile method for addressing the issue of methanol in distilled spirits using a compact near-infrared spectrometer

Methanol has been found in alcoholic drinks with increasing frequency, which is worrying because of its high toxicity. The presence of methanol in beverages occurs as an unintended consequence of fermentation processes, because of adulteration or the use of this substance in the preparation of counterfeit products. The identification and quantification of methanol in distilled beverages demands direct analytical methods that can be applied in the field to support inspection operations. This work describes a novel direct analytical method based on the spectral absorption characteristics of the third overtone (1100-1280 nm) of the near-infrared region to determine methanol in distilled beverages using a low-cost, compact spectrophotometer. Partial Least Squares (PLS) local regression models, for each spirit, and a global model based on the NIR spectra of 15 commercial samples, including eight types of distilled beverages, were constructed. While local models can perform better (Root Mean Squared Error of Cross-Validation, RMSECV = 0.12% (m m^-1) of methanol), the global model allows for broader application with sufficient performance to determine harmful levels of contamination in spirits (Root Mean Squared Error of Prediction RMSEP = 0.17% (m m^-1)) and high levels found in counterfeit drinks. In addition, the proposed method can also detect and determine the methanol content in adulterated fuel ethanol, often used to counterfeit distilled beverages, with an RMSECV of 0.42% (m m^-1), thus comprehensively addressing the issue of the occurrence of methanol in distilled beverages.