Determination of Alcohol Content in Beers of Different Styles Based on Portable Near-Infrared Spectroscopy and Multivariate Calibration

The determination of alcohol content in beers is essential for the quality control of this beverage. This paper proposed and validated a new rapid and direct multivariate method for this aim using a portable near-infrared (NIR) spectrometer and partial least squares (PLS) regression. Reference values were obtained by a gas chromatography with flame ionization detection (GC-FID) method developed and validated for this purpose. Aiming at building a robust model, a great variety of beers, from different styles, brands, and breweries, was incorporated into the model. NIR spectra were recorded between 908 and 1676 nm for 92 beer samples, corresponding to a range from 3.2 to 10.9% (v/v) of alcohol content. PLS model provided accurate results with root-mean-square error of calibration (RMSEC) and prediction (RMSEP) of 0.5% and 0.6%, respectively. The developed method was validated through the estimate of figures of merit, such as linearity, trueness, precision, analytical sensitivity, bias, and residual prediction deviation (RPD). In addition, an elliptical joint confidence region was calculated to verify the linearity, and confidence intervals based on the standard prediction errors were estimated for the validation samples.