Coffee fans can now indulge in their favourite drink in an eco-friendly manner. Mushroom mycelium (fungal root system) can now be grown directly on used coffee grounds; the process is quick, cheap, and relatively hassle-free compared to growing on sawdust or straw.

Mushroom growing can be done both cheaply and easily, with kits containing everything needed such as mushroom spawn, sawdust and growing medium available for a minimal fee. Or you could source all these materials yourself from various cafes who give away waste grounds free of charge or using homemade compost as the substrate base. Alternatively, mushroom spores may also be purchased as sawdust from companies specialising in mushroom spawn sales online.

Once the spawn has been mixed with coffee ground, it must colonise its substrate before producing mushrooms. This may take several days; to expedite this process it is beneficial to maintain temperatures of 20 degC (68 degF), providing optimal conditions for mushroom mycelium to rapidly multiply and spread out across its surroundings.

As soon as your mycelium has fully colonised and no coffee aroma remains, the jar should be relocated to an area receiving some light but no direct sun. A plastic bag punched with holes for airflow should then cover it for air exchange and you might consider placing a humidifier underneath to maintain humidity levels; additionally misting should take place regularly to prevent drying out of the bag.

After about one week has passed and the jar has reached the fruiting stage (when mushrooms start appearing), it should be taken out and placed into your kitchen, ready to be filled with freshly ground coffee or stored for future flushes.

Refrigerating the jar can also encourage fruiting; this process is called cold shock. Blue and white oyster mushrooms require cool temperatures in order to fruit properly; its significance decreases for yellow or pink oyster mushrooms.