There are two major classes of tannins: condensed and hydrolysable. Hydrolysable tannins aren’t as important in wine: if they’re present, they’ll have most likely come from the oak barrels the wine is fermented and/or aged in. The condensed tannins, also known as proanthocyanidins, are the main grape-derived tannins. They are formed by the polymerization of the polyphenolic flavan-3-ol monomers catechin and epicatechin. These subunits form chains of varying length, referred to by the unit ‘dp’ (for degree of polymerisation, i.e. the number of flavan-3-ol subunits). The main variables in the characteristics of these tannins are the length of the polymer chain and the nature of the individual subunits that compose it. In wine, the bonds between tannin polymers are repeatedly breaking and reforming. Thus a picture is emerging of a complex, dynamic process: the various phenolic subunits of tannins are sticking to each other and other chemical components of the wine in a sequential pattern, with these bonds being broken and reformed in a temporal sequence. No wonder it is a hard subject to study, and that only now, with highly sophisticated analytical devices, are scientists beginning to get a handle on tannins in wine.