We previously reported that the activity of yeat cells was maintained at high levels by aeration and agitation after sashimoto in shochu making during the long-term repetition of sashimoto. In order to apply this technology to shochu making with sweet patotoes, a pilot-scale test was carried out to demonstrate the technique developed in laboratory- and bench-scale studies. The reuse of stillage was studied in addition to reducing the discharge of stillage. By activating the yeast cells by aeration and agitation (0.1 vvm, 200 rpm) from 3 h to 9 h after sashimoto, the concentration of trehalose in cells maintained at a high level during the entire test period and the concentration of ethanol in the second-stage fermented mash was 13.1-13.8% (v/v). Reuse of the stillage was conducted using the stillage discharged from the atmospheric distillation, and the concentration of ethanol in the distillates obtained by atmospheric- or vacuum-distillation were 34.5% (v/v) and 34.8% (v/v), respectively. The flavor compounds were compared among shochu samples produced by the conventional method with and without the repetition of sashimoto as well as the reuse of stillage. Higher fatty acid ethylester tended to increase with the repetition of sashimoto. Higher fatty acid ethylester and higher alcohol in shochu produced by the reuse of stillage was slightly elevated. This shochu had a good body and stronger sweet potato flavor than any other shochu. The yeast strain seemed to be stable during the long-term repetition of sashimoto and the reuse of stillage according to the analysis of nucleotide sequences of NTS regions.
Appropriate excitation and detection wavelengths were chosen for measuring various parameters describing the activity of Aspergillus oryzae. The relationships between the mycelial weight in rice koji and enzyme activity were examined in order to develop a system for evaluation using fluorescence spectroscopy. As a result, we found that the best excitation and detection wavelengths for investigating Aspergillus oryzae were 410 and 630 nm, respectively. The fluorescence may be induced by the activity of Aspergillus oryzae because no fluorescence peaks were detected from sterilized rice koji. In addition, we showed that this system was not influenced by moisture content or glucose concentration, which both changed during the rice koji cultivation. The fluorescence emission strength was closely correlated with both the mycelial weight in rice koji and enzyme activity. Thus, fluorescence spectroscopy should prove suitable for evaluating the mycelia weight in rice koji, α-amylase activity, and acid carboxypeptidase activity.