PURPOSE: To obtain an accelerating culture base producible in a short time and suitable for the growth of mushroom by aging raw sawdust with lignin- decomposing microorganism and using the treated sawdust as a main component.

CONSTITUTION: Raw sawdust is mixed with lignin-decomposing microorganisms, nutrient sources, a necessary amount of water and a pH modifier (e.g., calcium carbonate or slaked lime) and aged by maintaining under proper temperature and humidity condition to promote the proliferation of the microorganism. The mixture is periodically turned over in the case of using an aerobic microorganism. The turn-over is carried out at the time when the temperature increase of the culture base is stopped and the temperature begins to decrease.