Saccharification
Japanese: 糖化
The conversion of polysaccharides like starch into sugars through enzymatic action. This reaction, driven by amylase from koji mold, is the first step of fermentation.
Saccharification is the reaction in which large molecules like starch are broken down into smaller sugars such as glucose by enzymes.
The starch in rice and barley cannot be directly used by yeast. Amylase secreted by koji mold converts starch into glucose, creating the 'food' yeast needs. The sweetness of amazake is precisely the product of this saccharification.
In sake brewing, saccharification and alcoholic fermentation proceed simultaneously—a rare technique called multiple parallel fermentation. Koji creates sugar while yeast converts it to alcohol, both reactions occurring in a single tank. This is a sophistication unique to Japanese brewing culture.