Procyanidins are condensed tannins consisting of polymerized subunits of epicatechin or catechin. They are structurally highly diverse because of the many possible combinations based on number of subunits, type of bonding, and branching. For convenience, procyanidins are typically characterized based on their degree of polymerization, with DP2 representing a dimer, DP3 a trimer, and so on. Procyanidins can be further distinguished by the type of bonding between subunits. For example, in B-type procyanidins (apples, cocoa) the subunits are connected by a single bond, which is predominantly 4β8 or less often 4β6.