Degradation of starch by amylases in beer brewing.

Abstract

In the beer brewing industry throughout the world about 8 × 106 tons of starch is annually converted into fermentable sugars and dextrins. Determining factors for the degradation of starch are the conditions of mashing and the action pattern of the amylases, α-amylase and β-amylase. Although present in germinating barley and in barley malt, α-glucosidase and debranching enzyme (plant pullulanase) exert little action in normal brewing procedures. Accordingly, the majority of the α-1, 6 linkages in amylopectin survive the brewing process. In a series of studies the formation and the composition of the dextrins present in beer wort have been examined by enzymic methods and quantitative gel filtration chromatography. The results show:-About 75% of the starch degradation products are glucose, maltose, and maltotriose. The remaining 25% constitutes the unf ermentable residue, generally known as dextrins.-About half of the dextrins consists of oligosaccharides with less than 10 glucose units, either linear or singly-branched.-About half of the dextrins contains 10 or more glucose units per molecule and may be termed megalosaccharides. These dextrins are multiply-branched.-The weight of the dextrins versus their molecular weight exhibits a characteristic pattern for which the term wavy distribution has been coined, inter alia to indicate that the dextrins in wort and beer seem to fall into distinct groups. Subsequent structural analysis has revealed that these groups of dextrins are characterized by their number of α-1, 6 linkages.-The multiply-branched dextrins in wort and beer represent structural entities of dense branching in the original amylopectin (starch) molecules. Thus the study of dextrins in brewing also provides information of the fine structure of starch. Based on these findings a model for the degradation of starch in beer brewing by a-amylase and β-amylase will be proposed.