rotterzwam sees a future in producing food locally instead of getting food from distant countries. This can be done by not considering coffee grounds as waste and incinerating them, but seeing them as input for a multitude of products. And by producing and consuming mushrooms as a substitute for meat, because it uses 600 to 1,000 times less water.

However, oyster mushrooms are not the final destination for rotterzwam. After the substrate has been exhausted, rotterzwam extracts enzymes from the mushroom mycelium. These enzymes are raw materials for bioplastics, biofuels and biodigesters, among other things. And the little bit left over? Rotterzwam composts this with the help of compost worms into first-class compost – which in turn is used to make BlueCity green.