Brown mould, white mould and grey mould
Refers to various forms of decomposition caused by wood-degrading fungi. The 3 main components of wood are cellulose, lignin and hemicellulose. Cellulose, which is made up of long twisted fibres, has the function of creating breaking strength in wood. In much the same way as concrete is given tensile strength by embedding an iron mesh (riven mesh). When the wood-degrading fungus breaks down the cellulose fibres, the breaking strength is removed and this degradation is called brown mould. With brown mould, the wood turns brown and cracks into blocks along and across the grain (fibre direction). House fungus, yellow dry rot, white dry rot, cork fungus and fan fungus are examples of brown mould-forming fungi.
Lignin, on the other hand, is the wood's "filler" - like the cement in a concrete mould. If the wood-degrading fungus breaks down the lignin in the wood, the cellulose strands will be left behind as distinct strands. This degradation is called white mould. With white mould, the wood is stringy and soft and does not crack. Coniferous wood does not change colour, darker hardwoods become bleached. White mould fungi include bark fungi and fireblight fungi.
With grey mould (surface rot), the wood turns grey and loses weight but retains its shape. Wet wood can be compressed, but regains its shape when the pressure is released. Small cracked blocks are formed when the wood dries out. Grey mould is caused by special fungi that form tunnels inside the cell walls of the wood as they decompose.
Mushrooms at a glance
