Amylopectin. This polysaccharide comprises between 65% and 85% of the starch molecule and is a branched glucan polymer produced by the formation of α-(1→6)-branch linkages between adjoining linear (i.e., α-(1→4)-linked) glucan chains. The other component of starch is amylose. It is the breakdown of these two starch components that creates the various sugars found in wort.

The distribution of glucan chain lengths and branch point clustering within amylopectin allows short- to intermediate-sized glucan chains to form double helices that can pack together in organized arrays, and this forms the basis of the semi-crystalline nature of much of the starch granule matrix. Starch granule formation is governed by both the semi-crystalline properties of amylopectin, as determined by the length of the linear chains of amylopectin, and the clustering and frequency of α-(1→6)-branch linkages.

Chemically, amylopectin has similarities to the animal storage compound glycogen, and both structures are produced by the same overall class of enzyme (glucan synthases). The majority of the α-(1→6) linkages in amylopectin will survive a “normal” brewing process.

Amylopectin, which is preferentially broken down during the malting of barley (or, at least, the chain length of the molecule is reduced), has one reducing chain end and numerous non-reducing glucose residues at the branch ends (amylose molecules have single reducing and non-reducing glucose residues at their chain ends). Therefore, when iodine solution is used for a starch conversion test, amylopectin imparts a reddish tint, whereas amylose gives the blue color.