Spectral Features Characterizing Rice Wine “<i>Sake</i>” Variety Using Mid-Infrared Spectroscopy

Abstract

We developed an infrared spectroscopic evaluation method of Sake (rice wine), whose quality and taste highly depend on the chemical contents, the interactions between the components, and the pH value, using a Fourier transform infrared (FT-IR) spectrometer equipped with an attenuated total reflection (ATR) accessor y. The objective of this study is to understand the spectral features of Sake and the main components because the component balances of the amino and organic acids originating from white rice as the raw material and being produced during brewing processes could closely relate to the Sake characteristics. The spectral features characterizing the Sake variety were mainly observed in four regions on the mid-infrared (MIR) spectra. The Sake varieties was able to be distinguished as a difference in the spectrum pattern by considering the pH dependence of the amino and other organic acids based on the ionic dissociation equilibrium theory. Furthermore, the Sake, which has almost a similar characteristic, such as the polishing ratio of the rice as the raw material is different by only 5% or the Sake product before and after it matured, could be identified on the spectral data. Consequently, the infrared spectral information analysis would be acceptable as a new method to evaluate a profile of Sake for the quality evaluation relating to the taste and the non-destructive on-line monitoring of the brewing process.