PREVENTION OF BROWN DISCOLORATION IN EUROPEAN OAKWOOD OCCURRING DURING KILN DRYING BY A VACUUM PROCESS - COLORIMETRIC COMPARATIVE-STUDY WITH A TRADITIONAL PROCESS

The efficiency of two kiln drying processes on brown discoloration developments of Quercus robur (L) and Quercus petraea (Lieb) was studied. A traditional atmospheric pressure system, was compared with other using vacuum and super heated steam. 103 green boards from three different trees were used. After each cycle (6), we analysed and compared the color of the boards using a spectrocolorimeter fitted with the CIELAB analysis. With the traditional system (in moist condition) we obtained 100% brown discoloration, in contrast to vacuum and super heating which did not develop brown discoloration. The brown discoloration is characterised by a decrease in lightness (-6 to -8 units) and color angle (-1 to -2 units) compared to non discolored wood. The discoloration is probably independent of wood origin and can be prevented by quick kiln drying without oxygen.