98.8% of the coffee biomass is wasted in the process of making a cup of coffee. One group in the Netherlands is determined to make use of the waste.

GRO Holland is recycling coffee grounds as a growth substrate for mushrooms. Waste grounds are collected from a network of cafes, mixed with oyster mushroom spores, packed into perforated plastic bags and hung in a humid warehouse. The mushrooms are harvested and sold back to the cafes. The waste substrate goes to nearby tulip farmers to reuse as mulch.

The organisation is now working on designs for a new visitor centre in which coffee grounds will be used in its rammed-earth walls and mushrooms will be used as thermal insulation in a cavity wall.