Torrefaction is an interesting option to pretreat biomass in order to obtain a fuel with improved handling and combustion characteristics, but there are a number of questions related to the supply chain and especially storage. To investigate the susceptibility of torrefied and charred spruce and birch to biological degradation, two experiments were conducted: a controlled laboratory fungal growth experiment with four different wood utilizing fungi and a preliminary field experiment with uncontrolled conditions. In laboratory, changes in moisture content, carbon and nitrogen contents and mass were measured, and the growth of the fungi was determined visually. Increasing pyrolysis temperature decreased fungal growth, but loss of carbon was noted in all of the samples. Fungal growth increased the moisture contents of samples. In the field experiment dry matter loss and increase of moisture content was noted. Torrefied wood and charcoal seem to not have full resistance towards fungal degradation. This creates additional problems that have to be taken into account when planning the supply chain of the material, as outside storage may not be advisable. (C) 2014 Elsevier Ltd. All rights reserved.