Oimizu (additional water added to the moromi)

Oimizu (追水) refers to the addition of water during the sake brewing process when the sugar content of the moromi (fermentation mash) has become high and fermentation is being suppressed. This water is used mainly to promote fermentation. Oimizu is carried out after the final addition of ingredients to the moromi (tome-jikomi), and it is an important step for keeping the moromi in better condition. The added water activates the yeast and lets fermentation proceed smoothly, which contributes to improving the quality of the finished sake. It is also known by the alternative name "Mizu Yondan" (水四段), which indicates that the process of adding water is divided into four stages. Because oimizu is performed on the basis of the skill and experience of an experienced toji (master brewer), how it is adjusted can have a significant influence on the flavor and aroma of the sake.