A technique, useful for studying the formation of kiln brown stain in wood drying, has been developed to measure the surface colour change in a single board wood sample during drying. The wood sample is planed carefully in the green state to remove any surface wood that was damaged during cutting. The intact tracheids at the surface cause the evaporative front to remain at the surface during drying and therefore colour formation also occurs right at the surface. In this way, the colour can be measured using a spectrophotometer at various stages during drying without having to slice the sample. Experiments were carried out to measure the change in colour of wood from green to EMC corresponding to the drying schedule used. At the end of each schedule the boards were held at the EMC to determine how the colour changed below fibre saturation point. The results show that the colour of the wood continues to change below the fibre saturation point and the nature of the colour change indicates an increase in the complexity of the coloured compounds present. Further experiments were done to measure the rate of colour development at different temperatures using the technique developed. The results have shown a correlation between temperature and colour development over the range 50°C to 70°C with the rate increasing significantly above 60°C

Experiments were undertaken to determine the effects of drying conditions (temperature and humidity) on the development of kiln brown stain in radiata pine during drying. Eight schedules were tested with temperatures ranging from 50°C to 120°C and relative humidity from 14% to 67%. The variables measured were moisture content, color expressed using the CIELab color space, and nitrogen content. The experiments have shown that the kiln brown stain is influenced by drying temperature and drying time. The recommendation is therefore that low-temperature and low-humidity schedules be developed for controlling color development.

Kiln brown stain in radiata pine (Pinus radiata) is a chocolate-brown discolouration that forms near the surface of boards dried at high temperature. This stain is the result of a thermochemical reaction between compounds in the sap that accumulate at the surface of the boards during drying. In this study, an attempt was made to remove the compounds that cause the stain, using bacteria in water sprinkled over the boards. Boards were stored in a tank, which was inoculated with rotted woodchips, with a recirculating overhead sprinkling buffer solution. Boards were periodically removed from the tank and dried under conditions that normally produce severe kiln brown stain (120/70°C). Samples were then removed to determine the level of stain by image analysis and the ease of moisture movement by neutron radiography. The bacterial treatment modified the extent of the stain layer so that after about 8 days of treatment there was no noticeable stain. The drying characteristics of the wood were modified so that the boards dried more slowly above fibre-saturation point, although the permeability of the dried wood increased