Bottle secondary fermentation method (Bin-nai Niji Hakko Hoshiki)

The bottle secondary fermentation method (bin-nai niji hakko hoshiki) is one of the techniques used to produce sparkling sake. In this method, moromi (fermentation mash) whose alcoholic fermentation has not yet finished is bottled without pasteurization. Because the yeast remains alive in the bottle, fermentation continues, and the carbon dioxide produced in the process is trapped inside the bottle. The technique is similar to the method used to make Champagne, and the secondary fermentation in the bottle produces sake with a distinctive effervescence and flavor. This method yields sparkling sake with a fresh aroma like that of sardines and a creamy mouthfeel.