Growing oyster mushrooms course

by admin on 21/11/2017

King oyster mushrooms

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I joined a course on how to grow oyster mushrooms in late November 2017 at Gruten in Oslo. Gruten, meaning the coffee grounds, was founded by Siri Mittet, who also held the course. Her business idea is to use the large amounts of coffee grounds, which would be given to compost and retrieved by a renovation company in the best case or thrown in the garbage in the worst case, for something useful. Having a bike with a large container, she cycles around in Oslo, visiting coffee bars and collecting coffee grounds. As she told us, the coffee grounds are pasteurised when coffee is made and ready for use. We also save time and energy if we use it as soon as possible after making coffee.

Gruten offers the following products:

The following courses are offered:

When Siri Mittet started the mushroom course, she presented a handout called: ‘From coffee cup to oyster mushrooms – how to grow mushrooms in coffee grounds’ with the most important points as follows:

  • Many mushrooms, including oyster mushrooms, consist of hypha, which often form a network, which is called mycelium.
  • The mycelium grows outwards, searching for nutrients and it uses enzymes to break down organic materials, next nutrients are absorbed through the cell walls. When the mycelium is sated or there is no more food, it will produce one or more fruitbodies  (what most people regard as a mushroom) in order to spread spores.
  • Coffee beans contain nutrients, which the mycelium needs: celluloseligninnitrogen and various minerals.
  • Used coffee grounds are hardly used, while they are in abundant supply at coffee shops and they can be gotten at a very low price.
  • Oyster mushrooms are fond of coffee grounds. The mycelium is able to extract nutrients from semi-sterile grounds at the right temperature range.
  • After growing of the mushrooms has finished, the growing medium can be used as compost or fertiliser.
  • Use only fresh and clean coffee grounds, to be mixed within 48 hours to minimise risk of mould.

After having learned a little about how to use coffee grounds as a growing medium, we set about preparing one bag for each participant in the premises of Gruten.

After having washed hands, we should disinfect a bucket with soap and water. Next, we used a digital scales to get 800g – 1kg coffee grounds, which we put in the buckets. 200g of spores was added to the grounds together with some water before mixing everything thoroughly. We also tore up cardboard into small pieces and mixed them with the coffee grounds and the spores. A thin layer of limestone was laid on the top because it leads to higher pH (less acidity) and a lower risk of contamination. Finally, the mixture was poured into a small, transparent plastic bag and the opening was closed by means of a piece of tape. However, since the mycelium has to be able to breathe, a permeable filter had already been attached near the top of each bag.

Having arrived at home, I kept the bag in a cupboard in my kitchen. The first 7 days are critical until the mycelium has got the upper hand on mould. After 3-5 weeks, the mycelium has colonised the growing medium and is ready to produce a fruit-body in order to make spores.

Next, the fruit phase where the following procedure should be followed:

  • lay the bag with a cut in a bucket with cold water and let it stay for 10 hours in order to trigger growth of the fruit body.
  • temperature around 20°C.
  • spray the growing medium with water 2-3 times a day.
  • the nascent fruit-body needs light, but not direct sunlight.
  • enough air – open the windows 2-3 times a day.
  • after 7-10 days the fruit-body starts getting formed, the first oyster mushrooms can be harvested abut one week later. the rest of growing medium is a good fertiliser.

Unfortunately, I didn’t succeed in making mushrooms, but the most important thing for me was to make it known that used coffee grounds have many useful purposes and that they should not be thrown in the garbage.


If you want to grow your own oyster mushrooms and you live in Norway, please consider buying growth bags and mushroom spores from Gruten!

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