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– How do we turn waste coffee into Gourmet Mushrooms?

Tuesday : 15th Nov

It’s a fair question – how do we turn waste coffee into Gourmet Mushrooms? Don’t most Gourmet Mushrooms grow on wood, straw, or horse manure? Well, yes they do – but the Pearl Oyster Mushroom is very versatile and is able to use waste coffee grounds as it’s food too. When a cup of coffee is made, less than 1% of the coffee beans end up in the cup. The spent grounds are still packed full of cellulose, lignin, nitrogen, sugars and other nutrients which the Mushrooms can make use of.

So, how do we go about it? Well first up is the collection of waste coffee grounds. We pick these up at the end of each day from large cafes in Plymouth, who would otherwise just throw them out with the rest of their rubbish. Usually with mushroom cultivation, you have to sterilise the compost you are going to grow your mushrooms on, but the beauty of growing on coffee waste is that the grounds have already been sterilised when going through their espresso machine. We then mix the coffee grounds with shredded cardboard that we buy from Paperchain – a recycling social enterprise based in Exeter. They collect waste cardboard from local businesses and shred it, and we add it to the waste coffee to help our mushrooms grow. The cardboard provides a dense source of cellulose and other nutrients, and creates good structure in the growing compost for the mushrooms to prosper.

We then add our own in-house grown  Mushroom spawn. We grow this ourselves in our lab to ensure that we have lots of high quality spawn to use. So we now have a mixture of waste coffee, shredded cardboard and fresh mushroom spawn – all made up under semi-sterile conditions, in the right proportions and adjusted to the correct moisture content. This is then loaded into special mushroom cultivation bags and incubated in the grow room for 3 weeks.

During this time, the mushroom spawn grows thousands of fine root-like threads (called mycelium) out in a network across the coffee and cardboard waste. This mycelium is able to break down the waste and extract valuable nutrient from it to use as it’s food. When it has finally grown across the whole compost mixture, it is now well established and ready to produce delicious Gourmet Mushrooms from. Some final checks to ensure each grow kit displays good healthy growth and then they are ready to be sent out to our customers. When a hole is cut in the bag, oxygen is introduced to the Myclium and in around 7 days time, tiny mushrooms then begin to emerge. You can then watch in amazement as every day the mushrooms double in size until around day 14 when they are ready to harvest and enjoy.


There is a lot more that goes on behind the process – but that, in a nutshell, is how we turn coffee and cardboard waste into Gourmet Mushrooms! If you’d like to grow your own delicously fresh gourmet mushrooms at home, why not give one of our growkits a go. See here for more info.


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