Condensed tannins are also referred to as proanthocyanidins. They are
oligomeric or polymeric flavonoids consisting of flavan-3-ol (catechin)
units. Hydrolysis under harsh conditions, such as heating in acid, yields
anthocyanidins. An example of a condensed tannin is procyanidin B2
(epicatechin-(4β→8′)-epicatechin; 1.90). In this case the interflavanyl
linkage is between C4 of the ‘lower’ unit, and C8 of the ‘upper’ unit. The
linkage can also be between C4 of one unit and C6 of the second unit.