The hydrolysis of starch by glucoamylase is to hydrolyze α-1 4 glucuronide bonds in turn from the non-reducing end of starch, and then cut off each glucose unit in turn to produce glucose. Glucoamylase has poor specificity, and it can hydrolyze α-1 4 glucuronide bond. α-1, 6 bond and α-1, 3 bond, but the hydrolysis speed of the latter two bonds is slow, because the viscosity of sugar solution decreases slowly and the reducing ability increases rapidly when the enzyme acts on starch paste, so it is also called glucoamylase, and the hydrolysis ability of glucoamylase from different microbial sources is also quite different.

Liquor-making koji is made because there are a large number of microorganisms growing on koji, as well as enzymes secreted by microorganisms (amylase, glucoamylase and protease, etc.). Enzymes have biocatalysis and can accelerate the conversion of starch and protein in grains into sugars and amino acids. Sugar is decomposed into ethanol under the action of yeast enzymes, that is, alcohol. Tillers also contain many such enzymes, which have saccharifying effect. The starch in the tiller itself can be converted into sugar, and then converted into ethanol under the action of yeast. At the same time, koji itself contains starch and protein, which is also the raw material for brewing.