What is the main role of koji in sake production?

Koji plays a crucial role in sake production, primarily through the process of converting starches that are present in the polished rice into fermentable sugars. This transformation is achieved by the specific molds, primarily Aspergillus oryzae, which are cultivated on steamed rice during the koji-making stage. The enzymes released by the koji mold break down the starches into sugars, which are essential for the subsequent fermentation process carried out by yeast. This conversion is a vital step, as it directly influences the yield of alcohol during fermentation and impacts the overall flavor profile of the sake.

Other processes like polishing the rice, fermenting sugars, and stabilizing flavors are significant in sake production but do not define the specific function of koji. Polishing the rice is an important preparatory step that determines the purity and quality of sake, but it does not involve koji directly. Fermenting sugars relates to the action of yeast during fermentation and not to the direct function of koji. Stabilizing flavors is also essential in ensuring a balanced sake but does not highlight the primary role of koji in the conversion of starches to sugars.