Growing oyster mushrooms on spent coffee grains

The following items are required:

Inoculated oyster mushroom plugs, spent coffee grains from the coffee machine with or without the coffee filter papers (you can mix in some tea leaves too), a suitable container (large glass jar, a bucket or a strong plastic bag).

The still wet coffee grains are put into the container as soon as they are cold and an inoculated mushroom plug is pushed down into the mixture. The container should be covered up to keep the contents moist and stored at a temperature of 20 - 30° C. You can add more spent coffee grains at regular intervals each time you make coffee  (ideally daily) until the container is full. Push in another inoculated plug each time you add more coffee grains. If you are also including the coffee filters, you should press them down well into the container. The white mushroom mycelium should already be visible after a few days. If mould starts to appear, it should be removed. The oyster mycelium is usually effective at conquering against the mould.

The fruiting body of the mushrooms should start to grow when the mycelium has grown throughout the coffee grains (see photos page).

The mushroom culture now needs a bit of light and the cover should be partially removed to allow the exchange of air (important)! However, the mycelium and the first signs of mushrooms should not be allowed to dry out. If necessary, spray the mycelium and the coffee grains with water from time to time to keep the mixture moist.

The total time required until you can harvest the first mushrooms is approx. 6-8 weeks.

The mushrooms can be harvested when the cap size is about 3 - 5 cm in diameter. You should then get 1 or 2 additional harvests.  When the coffee grains are exhausted, they can either be composted or put onto moist straw bales in the garden to grow more mushrooms.

Single inoculation’ with a larger quantity of spent coffee grains
(e.g. from a restaurant)
You can also use larger amounts of coffee grains without the coffee filter papers. Fill a strong deep freeze bag with coffee grains (approx. 3 litres) and add about 10-12 inoculated plugs, mix in well and press down the coffee grains. Store the bag in a warm place. It should be opened to allow air to penetrate every couple of days. When the mycelium has grown throughout the coffee grains, proceed as described above. Open the top of the bag and spray occasionally with water to ensure that the mycelium on the surface does not dry out. Here too, the culture needs about 6 to 8 weeks before the mushrooms start to grow.

Nicola Krämer, Hannover * Marketing of mushroom-growing products * Home