Determination of quality parameters of beers by the use of attenuated total reflectance-Fourier transform infrared spectroscopy

The estimation of important quality parameters of beers, such as original and real extracts and alcohol content, has been evaluated by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) using a partial least square (PLS) calibration approach. Two sample populations, one consisting of 24 samples and other of 21 samples, obtained from the Spanish market and covering different types of beer were used. The first set was used for building and validating the model, whereas the second, measured 6 months after, was used for evaluating its robustness. The spectral range and the size of the calibration set and its suitability for building the PLS model have been evaluated.Considering a calibration set comprised of 12 samples, selected via hierarchical cluster analysis, and a validation data set of 11 samples, the absolute mean difference (dx−y) and standard deviation of mean differences (sx−y) of the real extract, original extract and alcohol content were 0.009 and 0.069% (w/w), −0.021 and 0.20% (w/w) and −0.003 and 0.130% (v/v), respectively. The maximum error for the prediction of any of these three parameters for a new sample did not exceed 2.5%. These values were practically invariant for both tested data sets.The developed methodology favourably compares with the automatic reference methodology in terms of speed and reagent consumption and waste generation.