Starch Conversion Enzymes
Starch conversion enzymes convert the starch in grist to flavor components and fermentable sugars. Starch is glucose molecules linked together in a linear polymer (amylose) or a branched polymer (amylopectin). Several key enzyme groups, primarily amylases, take part in the conversion of grain starches. Alpha-amylases rapidly but randomly break starch molecules to produce water-soluble fragments of starch called dextrins – unfermentable carbohydrates that contribute to beer flavor, body, and mouthfeel. Beta-amylases act only at the ends of starch molecules and fragments to produce maltose. Glucoamylases break off single molecules of glucose from starch molecules, dextrins and maltose.
The bonds that form branches in amylopectin polymer starch are resistant to the action of amylase enzymes. Pullulanase, a starch-debranching enzyme, can break these bonds and give amylase enzymes faster access to starch molecules. Cellulase and lipase break down cell walls and lipid inclusion complexes to release starch for conversion.
Using specific combinations or blends of all these enzyme types, a brewer can control starch conversion to increase extract and control attenuation, balance carbohydrate profile and assure consistency even with varying raw material.