Furfural is formed during the thermo-mechanical defibration of wood consuming the wood polyoses in acid dependent reactions. Thus, the formation of furfural requires the presence of organic acids like acetic or formic acid already present in the wood or formed during the thermal treatment, respectively. The formation of furfural is correlated with the temperature during cooking and defibration as well as the duration of the refining process. The higher the temperature and the longer the digestion time, the formation of furfural increases. Lowering of furfural contents in the wood fibres can be achieved by reducing pressure/temperature, digestion time
and by neutralizing the acidity of the wood. Alkaline additives, however, increase the oxidative cleavage of fatty acids, which leads to the formation of malodorous aldehydes. Fatty acid esters are present in all woods, contents are especially high in pine, birch or poplar e. g. It was found that a pronounced suppression of the formation of these aldehydes is achieved by addition of a combination of alkaline and complexing agents. This technical solution can be used to minimize the health risk from the emissions of aldehydes, including furfural from wood fibers and insulation products made from it.