Rotterzwam: coffee grounds for mushrooms

Who would have thought coffee grounds could be circular? In fact, they are ideal as a fertile substrate for growing oyster mushrooms. Rotterdam-based Rotterzwam collects the coffee grounds from local pubs, large corporations and restaurants. They cultivate the mushrooms and sell the produce to customers in the Rotterdam area.

Rotterzwam mixes the coffee husks and mushroom and spawns them in a bag that is hung in a special grow room. In May 2019, Rotterzwam opened new grow rooms in the Schie harbour in Rotterdam. In eight former reefer containers, 6,000-7,000 kilos of coffee ground is converted into 1,200-1,400 kilos of mushrooms monthly.  

The oyster mushrooms are fully grown and harvested in 6 weeks. Up to 50 kilos of mushrooms can be picked every week. Most of the produce is sold to restaurants, shops and private customers in the local area.

The entire process is sustainable and local - an outstanding example of the circular economy