Beer contains over 450 characterized constituents. Changes in the amount of alcohol or sugar produce a change in flavor. The quantitative determination of alcohol and real extract, for tax and taste purposes, is generally performed using a distillation method.

Diedrich Harm and co-workers, Research and Teaching Institute for Brewing, Germany, have combined near-infrared (NIR) spectroscopy and refractometry to determine the concentration of alcohol and real extract in various beer samples. This enhanced the precision of the measurement compared to single spectroscopic measurements. Light scattering effects were eliminated with applied mathematical pretreatments, with a linear baseline correction providing better results than a first deviation correction.

Results obtained for the beer samples were comparable to those of previous studies and the root mean squared errors of validation was 0.12 Mas%. A standard deviation value of 0.01 for alcohol with respect to real extract improved on previously reported values.

• Determination of Alcohol and Extract Concentration in Beer Samples Using a Combined Method of Near-Infrared (NIR) Spectroscopy and Refractometry
  S. Castritius, A. Kron, T. Schäfer, M. Rädle, D. Harms,
  J. Agric. Food Chem. 2010, 58.
  DOI: 10.1021/jf1030604