Abstract
The measurement of ethanol concentration in solution by near-infrared (NIR) spectroscopic analysis is generally used. On the other hand, in alcoholic beverages analysis, especially an analysis of Japanese sake, the ethanol concentration assay by this method is so far undeveloped. Coexistent compounds in Japanese sake have one or more absorbance peaks in the NIR area, and these absorbance peaks overlap with that of ethanol. Thus, the influence of coexisting compounds in Japanese sake could not be ignored in previous NIR spectroscopic analysis. Recently, according to selecting wavelengths in the NIR area, the measurement of the ethanol concentration in Japanese sake by a NIR spectroscope was developed; this equipment allowed us to measure the ethanol concentration of Japanese sake directly. In this work, by using a NIR spectrometer and a distillation-oscillatory densimeter, the ethanol concentration in sixty-four sorts of Japanese sake produced in many regions in Japan was analyzed. For an ethanol concentration from 13 % to 18 % (v/v), the values from the two methods were consistent with that displayed on these bottles and packs; most of the standard deviations in the NIR spectrometer were less than those of the conventional method. Moreover, the geographical influence on the measurement of the ethanol concentration, such as room temperature, room humidity, and any slight change of the voltage in the room, was not observed in both of these methods.
