The typical pretreatment method for enzymatic hydrolysis of
starches to fermentable sugars is based on a two-step method. In
the first step starch is liquefied by heat-stable a-amylase (EC
3.2.1.1) in order to decrease the viscosity of gelatinized starch solution
and to produce short-chained dextrins, by breaking down the
a-1,4-glycosidic bonds in the middle of amylose and amylopectin
chains. During the second step of starch hydrolysis (saccharification)
the dextrins are saccharified by glucoamylase (amyloglucosidase,
EC 3.2.1.3) to obtain monomeric sugars (glucose). Often
supportive enzymes, like proteases, cellulases, pullulnases and others,
are used to increase the amount of fermentable sugars,
decrease the viscosity of the mash and produce free amino nitrogen
that is used as a nutrient for yeast