Starch
Japanese: デンプン（澱粉）
A polysaccharide plants use to store energy. The main component of rice and barley, it becomes the raw material for fermentation after saccharification by amylase.
Starch is a polysaccharide made of hundreds to thousands of glucose molecules linked together. About 75% of rice and 70% of barley is starch.
Microorganisms cannot consume starch directly. Amylase secreted by koji mold breaks starch into smaller sugars that yeast and other microbes can use. This saccharification step is the starting point for grain-based fermentation.
The sweetness of amazake comes from starch converted to sugar by amylase. Sweet without any added sugar—proof that enzymes have 'transformed' the starch.