Soe koji (koji for the first addition)

Soe koji is the koji used in the first addition (初添, also called 添仕込み) when preparing the moromi (fermentation mash). Koji plays an important role in sake brewing: it breaks down the starch in rice into sugar and supports the process by which yeast then converts that sugar into alcohol. Soe koji is used at the first stage of the mash preparation and helps promote fermentation of the moromi. Other koji are used in later steps, namely naka koji and tome koji, each supporting fermentation of the moromi at a different point. Because the way these koji are used changes the quality and flavor of the sake considerably, sake breweries pay close attention to how they are applied.