A Guide to Growing Mushrooms
in Used Coffee Grounds
Lasse Melgaard is a co-founder of Two Raccoons, a company who specialise in making fruit wine from surplus fruits. Passionate about homebrewing and microbiology, Lasse is also an expert in mushroom growing! He’s created this guide to teach you all about growing delicious oyster mushrooms out of used coffee grounds.
So, how do you do it?
Growing mushrooms is often seen as a mysterious and complicated process. They’re seemingly so unpredictable, suddenly and spontaneously popping up at random - in forests and gardens alike. But by understanding the life cycle of mushrooms, growing your own delicious oyster mushrooms will be one of the quickest and easiest ways of becoming a glorified food waste wizard.
Wood-loving mushrooms, such as oyster mushrooms, grow on decomposing fibres, such as wood, coffee grounds, and even denim jeans. During the summer, they gather nutrients by growing their roots (or mycelium) inside a tree trunk or under the shade of leaves. Once autumn comes around, the leaves fall. The sun hits the tree trunk, moisture in the air increases, temperatures drop... and mushrooms start appearing!
If you can provide these two environments (warm shade and cool humidity), you'll find yourself with a crop of mushrooms on your hands. (No, not literally!)
Ready to grow some mushrooms on coffee grounds? Let’s go!
- 3-5L bucket with a lid.
- 50-100g oyster mushroom spawn or mycelium from a sustainable source.
- Freshly used coffee grounds.
- Get your bucket ready.
- Make two 2cm holes on opposite sides of the bucket. Cover the holes with masking tape or micropore tape you can get from a pharmacy.
- Collect coffee grounds.
- Sit back, relax and enjoy a coffee (made with coffee grounds) or ask a local cafe if you can have some of their freshly collected coffee grounds.
- It’s important to note that the coffee grounds shouldn’t be more than a day old or this will affect the quality and success of the mushrooms.
- The coffee grounds should be moist but not dripping wet. Try squeezing them gently with clean hands to remove excess water.
- Start with about 500g to 1kg of coffee grounds (later, you’ll continue to fill up the bucket over time as you consume more coffee!)
- Mix the mycelium and used coffee grounds.
- Fill the bottom of the bucket (about a quarter to a third of the bucket, but less is fine too) with freshly brewed coffee grounds cooled to room temperature.
- Mix the entire bag of mycelium with your spent coffee grounds. Close the lid afterwards.
- Wait a few days until you can see a white layer of mycelium has grown on top of the coffee grounds. You can take a sneak peek now and again, but make sure to close the lid after.
- Keep adding coffee grounds until the bucket is full and white with mycelium.
- Once the mycelium has created a white layer, you can add more coffee grounds on top every 1-2 days. You don’t need to shake or stir the mix.
- Make sure to close the lid after you've added your coffee grounds.
- Let it grow.
- Once the bucket is full of mycelium-covered coffee grounds, move the bucket to a cold place for 24 hours. This will act as a signal for the mushrooms that it’s time to grow!
- Once you see the mushrooms peeking out from under the tape, give them a few sprays of water once a day to stop them from drying out.
- Harvest time!
- Once the mushrooms have stopped doubling in size every day (!), harvest them by twisting the mushrooms off the bucket. Consume at your own delicious risk, with lots of butter, garlic, herbs and sustainably sourced oil on crusty bread!