Migration of Kiln Brown Stain Precursors During the Drying of Radiata Pine Sapwood

Abstract

Kiln drying of radiata pine (Pinus radiata D. Don) sapwood causes the formation of a brown discolouration, commonly called kiln brown stain. Kiln brown stain occurs just under (0.5-2mm) the wood surface but subsequent skim-dressing exposes the stain causing substantial economic loss in the New Zealand high-value lumber export markets. The present study quantified the changes in water-soluble compounds occurring at the wood surface and the centre of radiata pine sapwood boards (100 x 40 mm) during kiln drying at 90/60°C and 120/70°C. The results of the study showed that during kiln drying redistribution and concentration of water-soluble sugars and nitrogen containing compounds occur from the centre to the surface of radiata pine and this induces kiln brown stain. An Amadori-Maillard reaction is the likely cause of kiln brown stain formation in drying of radiata pine.