The rather novel picture of chestnut wood tannin, in situ in the wood, which emerges from matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) is that of a pervasive and extended random tridimensional macromolecular network, formed by pentagalloylglucose clusters linked to each other, to form chains and encrust the wood constituents matrix. Up to pentagalloylglucose trimers were identified in the MALDI-TOF analysis of the commercial chestnut tannin extract, which were clearly degradation products of more extensive chains likely to be present in situ in the wood before extraction, in the network through polygallic/ polyellagic chains or flavogallonic acid bridges. The hydrolyzable chestnut tannin network is capable of being extracted, to yield the commercial chestnut tannin extract exclusively by its degradation, a degradation that is possible only because of the susceptibility to hydrolysis of the ester bridges holding the network together. Internal rearrangements of the fragments formed by the extraction appear to occur readily and with ease, to yield a variety of structures characterized by the presence of ellagic acid residues, flavogallonic acid residues, and also, but less readily, nonahydroxytriphnoic acid residues. The other main constituents of the commercial tannin extract, castalagin and vescalagin, are shown to be simply the more stable degradation plus internal rearrangement products derived from the hydrolysis of polypentagalloylglucose chains.