Optical measurements and pattern recognition techniques for autheticating top-fermented and bottom-fermented beers and predicting the alcoholic strength

Two innovative non-conventional optical techniques were used to measure a collection of 70 commercial beers. Two beer types were considered, depending on the yeast used and temperature of fermentation: the top-fermented and bottom fermented, respectively. Top-fermented beers were produced with saccharomyces cerevisiae yeast between 15°-20°C. Bottom-fermented beers were produced with saccharomyces uvarum (or pastorianus) between 7° and 12°C. 47 samples were golden Ale and Weiss beers (top-fermented), while 23 samples were golden Lager (bottom-fermented) beers. Their alcoholic strength varied in the 0.5-9.5%vol range. Color and turbidity were measured by means of scattered colorimetry, that is multi-wavelength and multi-angle spectroscopy performed in the visible band. Scattering-free diffuse-light absorption spectra in the near-infrared band were measured by means of an integrating sphere. A multivariate processing of spectroscopic data was applied. The scattered colorimetry data showed beer discrimination according to fermentation method. The diffuse-light spectroscopy data provided prediction of alcoholic content.