A STUDY OF SOME FACTORS PROMOTING KILN BROWN STAIN FORMATION IN RADIATA PINE

Kiln drying of radiata pine (Pinus radiata D. Don) sapwood induces a b rown discolouration, commonly called kiln brown stain. Kiln brown stai n generally occurs 0.5-1.5 mm under the surface of the dry sawn lumber . However, subsequent planing of the wood can expose the stain causing substantial revenue loss in the New Zealand high-value export markets . In the present study, the effects of kiln schedule temperature, wood moisture content and kiln relative humidity on kiln brown stain forma tion were investigated. The results showed that kiln brown stain was g reatly reduced by using kiln schedules of less than 50 degrees C as op posed to 90 degrees C and was also more pronounced in the kilning at 3 0% kiln relative humidity, than at 80% humidity. Furthermore, the occu rrence of kiln brown stain tended to intensify with decreasing wood mo isture content, irrespective of kiln temperature and kiln humidity use d. The practical implication of this work and the mechanisms of kiln b rown stain formation are discussed.