Biochemical catalysis by enzymes can hydrolyse starch in very specific ways.
The role of α-amylases
α-Amylase breaks the starch chain in such a fashion as to produce only minor amounts of low and medium molecular weight sugars but major amounts of soluble higher saccharides.
The role of β-amylases
β-Amylase breaks the starch chain at every other unit bond, producing optimal quantities of the disaccharide maltose.
The role of glucoamylases
Glucoamylase hydrolyses the starch chains unit by unit, producing large amounts of dextrose in the hydrolysate.
The role of isoamylases and pullulanases
Pullulanase or isoamylase hydrolyse the branching points of amylopectin allowing higher maltose and glucose yield.
Current processes use thermostable bacterial α-amylase in the first step breaking down the starch into oligosaccharides, which are then broken into glucose molecules by use of fungal glucoamylase.