The influences of log storage and kiln drying climate on the colour of non-steamed beech (Fagus sylvatica L.) wood

Abstract

Discolouration during the drying of non-steamed beech is a major industrial concern. The generally preferred yellow-white colour can easily develop a reddish or dull grey appearance during drying. In this study, the influences of log storage time and kiln drying climate on the colour of non-steamed sawn beech have been investigated and quantified. Samples 27×87 mm in cross section were dried in laboratory kilns and the average colour, in CIELAB colour space was measured on dry planed surfaces using a photoelectric colorimeter. Log storage for 13 weeks under low-temperature conditions had no visible effect. The reddish discolouration is mainly temperature related while the greyish discolouration is mainly controlled by the equilibrium moisture content (EMC) during the initial drying. Within the investigated climate interval, the EMC was twice as important as temperature for the final colour. Regression models developed show that, as long as the EMC is kept below 15%, a temperature of up to 37°C can be allowed without any visually detectable discolouration.

Keywords:

• Beech
• discolouration
• Fagus sylvatica
• kiln drying
• log storage

Acknowledgements

The work presented in this paper has been financed by the Swedish Knowledge Foundation, the Swedish Hardwood Institute and Tarkett AB, which is gratefully acknowledged. The author would like to thank Mr. Jens Lundgren at Tarkett for practical assistance during sawing, drying and sampling as well as Mr. Nils Larsson at Linköping University for assistance with the SEM samples. Appreciation also goes to Prof. Thomas Thörnqvist and Prof. Tom Morén for assistance when preparing this paper.