The effect of diluting with water（warimizu） used to adjust the alcohol concentration before bottling on sensory tests of Japanese sakes was investigated among three breweries in Hiroshima. Japanese sake samples were diluted with reverse osmosis membrane filtered water and organoleptically compared to those diluted with unfiltered water. It was found that Japanese sake tastes such as “rich body”, “aftertaste”, “umami”, and “matureness” were reduced with Japanese sake samples diluted with reverse osmosis membrane filtered water. These results were recognized with both a Honjozo sake and a Junmai sake of Brewery A. This reduction was found to be stronger in sweet types of sake than in dry types of sake of Brewery B. However, this reduction seemed to be much smaller in the Junmai-ginjo sake of Brewery C stored under −4℃ in bottles. This reduction could be significantly observed between the waters diluting the sake samples whose differences of hardness ranged from 16 to 32. Considering the variety of water hardness in Japan, the diluting water（warimizu） could be an important factor in producing each characteristic of Japanese sakes throughout Japan.

Previously, we have examined the one-step and the three-step（Stimula Sauvignon Blanc, addition at third step Tome; Optimum White, addition at the day before pressing）preparations for fermentation mash with the use of fermentation nutrients for wine（Stimula Sauvignon Blanc and Optimum White, Lallemand）, their addition improved the utility efficiency of raw materials and enhanced the aroma of the brewed sake. In this study, we have investigated differences due to the timing for adding by the three-step（addition at koji and water mixture Mizu-koji or first step Soe）preparation for fermentation mash using wine and sake yeasts. In the case of using wine yeast, the effect of Mizu-koji or Soe in the addition of fermentation nutrients Stimula Sauvignon Blanc was higher than Tome in the previous report, while there was hardly any difference in Mizu-koji and Soe. Although this was not as remarkable as the previous results of the one-step preparation for fermentation mash, the addition of Stimula Sauvignon Blanc improved the utility efficiency of raw materials and enhanced the aroma of the brewed sake in the use of wine yeast. It was suggested that its addition improved the fermentative metabolism in sake brewing using wine yeast. The effects of their addition in the case of using sake yeasts were smaller than that of using wine yeast, the same as in the previous report. However little difference was observed in the timing for adding among Mizu-koji, Soe and Tome. From these results, in the case of using wine yeast, adding at the early stage of the sake brewing process is effective at the time for the addition of the fermentation nutrients for wine used in this study. In the case of using sake yeast, the timing for adding fermentation nutrients for wine does not have so great an influence on the quality of the sake.