Koji starter for shoyu (soy sauce) are a specialized strain of *Aspergillus oryzae* used in the fermentation process to break down soybeans and wheat. In shoyu production, koji spores are inoculated onto a mixture of steamed soybeans and roasted wheat, initiating fermentation by producing enzymes that convert proteins and starches into amino acids and sugars.  The quality of the koji is crucial for producing authentic, deep-flavored shoyu.

This spore is well-adapted to the salty environment needed for soy sauce production. The brining process in soy sauce creates a high-salt condition, which can inhibit many microorganisms, but this spore can still function and produce the necessary enzymes in this environment. 

Additionally, this spore is selected for the ability to support a slow fermentation process. Unlike koji for sake, which is designed for faster fermentation, soy sauce koji is cultivated for prolonged fermentation that can take months or even years. This extended time is vital for developing the complex and rich flavors that characterize soy sauce.