Möttönen, V. and Luostarinen, K. 2005. Discolouration of Sawn Birch (Betula pendula) Timber from Plantation Forests during Drying: The Role of Proanthocyanidins (Condensed Tannins) in Discolouration of Birch Wood. Baltic Forestry, 11 (1): 13-20

In the previous paper on discolouration of sawn birch timber from plantation forests that had been published in Baltic Forestry, 2004 10 (2), the effect of external factors (growing site, felling season, log storage) was discussed. In this paper, the role of proanthocyanidins in discolouration during drying is investigated. Conventional warm-air drying gave the highest concentration of proanthocyanidin in the wood. Storage of wood as logs increased the proanthocyanidin concentration in both fresh and dried wood. Proanthocyanidins obviously polymerised and oxidized to coloured compounds during drying, as the proanthocyanidin concentration was found to be lowest in the darkest reddish wood. The combination of drying temperature and prevailing moisture content of wood during the drying process seemed to be very important for formation of coloured phenolic compounds.

Key words: Proanthocyanidins, silver birch, wood discolouration, wood drying.