How to grow mushsrooms using old coffee grounds in a glass jar. This is the ultimate science experiment for kids and big kids like me!
Your morning cup of filtered coffee only uses 1% of the grounds nutrients. It seems insane to throw something away that has 99% of its power left! Mushrooms are nutrient hungry and thrive in coffee grounds. So you can grow food using food waste to reduce food and packaging waste, how cool is that!?!
You don’t need any specialist equipment, just a simple glass jar. The set up is relatively low cost and it’s surprisingly easy to grow mushrooms this way. Growing mushrooms in a reusable glass jar makes this process even greener, but it also means you can watch the whole process of how mushrooms grow.
It’s also super quick. In the right conditions Blue-grey oyster mushrooms take 3-5 weeks to grow. Blue-grey oyster mushrooms are a healthy addition to omelet’s and stir fry’s. They pair well with white meat and seafood. Or simply enjoy them grilled/roasted with breakfast.
Contents
How to Grow Mushrooms In Coffee Grounds
This is a new adventure for me. I’ve never grown mushrooms before this, but I’ve done the research! This how to grow mushrooms post is a simplified guide for beginners. I’m going to explain the different stages and terminology in my own language and my understanding of the process. Coffee grounds and a glass jar is as complex as it gets, so don’t be afraid!
What mushrooms can you grown in coffee grounds?
Oyster mushrooms are perfect for growing in coffee grounds using a glass jar. There are 5 main varieties that are happy to grow this way; blue-grey, white elm, yellow-gold, pink, and king.
Blue-grey oyster mushrooms are the most forgiving variety and are happy in cooler climates. This makes them perfect for beginners in the UK.
Yellow-gold and pink oyster mushrooms need a warmer environment so are best grown in spring and summer.
What do I need to grow mushrooms at home?
A supply of used coffee grounds
100ml (60g) Blue-grey mushroom grain spawn (available online, see link below)
A 1l glass jar with metal lid (lid needs 2x 1cm holes drilled/punched into it)
70% Isopropyl alcohol wipes (available at pharmacies and online)
Micropore tape (available at pharmacies and online)
A large metal spoon
How To Grow Mushrooms
Mushroom spawn
Mushrooms seeds that you will plant in the coffee grounds.
I ordered my 60g of blue-grey oyster mushroom spawn from Urban Farm It. They seemed reputable, they had extensive advice on their website and they were quick to respond to a query I had. I’ve never bought mushroom spawn before so they seemed like a good place to start.
Here is the link to their website https://urban-farm-it.com/
This is not an advert for Urban Farm It. I paid for my products, I was happy with their service/product, so I was happy to share their details with you.
Sterilise
To remove bacteria and mould spores from the work area and equipment you will use.
Bacteria and mould will compete with your mushrooms to grow. Mushrooms will put up a good fight, giving them a sterile environment will increase their chance of winning!
This is going to sound intense. I promise it isn’t and it quickly becomes second nature.
Your hands
Wash your hands with soapy water, dry and use hand sanitiser. Clean your hands this way before you start, or handle any sterilised equipment.
Glass jar and metal lid
Wash in hot soapy water. Shake off excess water and place on a baking tray. Place in a pre heated oven at 180C for 15 minutes. Remove the tray from the oven and allow the glass jar to cool before using.
Metal spoon
Submerge in boiling water for a couple of minutes. Allow to cool before using.
Work surface
Spray work surface with a regular antibacterial spray and wipe with kitchen roll. Then wipe down with an alcohol wipe.
Substrate
Growing material (soil) for mushrooms.
You can use any variety/brand of ground coffee. Sawdust and straw are also popular substrates. I use coffee because the grounds are a waste product, they are free and I enjoy a morning coffee.
Pasteurise
The sterilisation of the substrate (coffee grounds).
A benefit of using coffee is that brewing coffee is the pasteurising process, so sit back and enjoy a cuppa whilst others are boiling sawdust to grow mushrooms!
Use 4-5 table spoons of fresh coffee grounds and brew in a filter coffee machine, stove top coffee maker, or pour over coffee maker. These types of coffee makers are good as they allow the grounds to drain freely. I use my filter coffee machine for this. I allow the grounds to drain (and cool) in the filter for 4 hours. You could use a cafetière, but you will need to make sure excess coffee can drain away freely. Your coffee grounds don’t want to be sodden.
Do not use coffee grounds older than 24 hours. Mould and bacteria will have set up camp and will compete with your mushroom spawn to survive. 🍄 vs 🦠 – my moneys on mushrooms!
If you don’t drink filtered coffee you could ask your local coffee shop for their grounds. You would need to supply them with a sterilised container to knock the coffee into and use the grounds within 24 hours.
A bistro I like to visit, KOO, bag their grounds up at the end of the day for people to take for their compost heaps. I was cheeky and asked if they would knock coffee grounds into a sterile tub for the day. They kindly agreed so a huge thank you to them for assisting me on my mushroom adventure!
Inoculate
Mixing your mushroom spawn with the coffee ground.
Once your coffee grounds have cooled and the excess coffee has drained away, spoon the grounds into your jar. Open the bag of spawn and tip into the jar and mix into the coffee grounds. Close the lid and cover the two holes with micropore tape. This allows the mixture to breath and stops bacteria and mould from entering the jar. Wipe the outside of the jar with an alcohol wipe.
Clean hands, sterile equipment, and sterile work surface are key at this stage.
Incubate
Providing a warm dark space for the mushroom spawn to develop its root structure (mycelium).
Now place the jar in a warm (18-20C) dark place.
Colonisation
When the root network (mycelium) takes over the coffee grounds.
Now for the cool part! Check your jar daily for signs of colonisation. The coffee grounds will turn white and fuzzy when colonising. Sound disgusting, but it’s really fascinating and the glass jar gives you a good view.
When your grounds are completely white it’s time to brew another pot of coffee.
Clean your hands and sterilise your equipment and work surface. Use an alcohol wipe to clean the outside of the jar before you open it.
Brew another 4-5 table spoons of coffee and repeat as before. When the grounds are ready spoon them into the jar and level it off, do not mix into the existing grounds.
Close the lid, clean the outside of the jar with an alcohol wipe, and put the jar back in It’s warm dark place.
Continue this process until the coffee reaches the neck of the jar. You need to leave a little gap between the bottom of the neck and the lid.
Blue and fuzzy means mould! The odd speck should be fine. If your jar is full of it, you will need to restart.
Fruiting
Encouraging your jar of root structure (mycelium) to grow mushrooms.
When the jar is completely white and fuzzy it’s time to grow some mushrooms. Remove the lid of the jar, place in a bright and cool location (away from direct sunlight) and cover with a damp kitchen roll. Spray the kitchen roll with water daily to keep it damp. The drop in temperature, light and humidity will encourage the mushrooms to grow. Tiny mushrooms will appear and these are known as pinheads. When the mushrooms grow you can remove the kitchen roll. Mist as required to add a little humidity, you don’t want the jar to fill with water so mist lightly.
Harvesting
The mushrooms are ready to harvest when the heads start to flatten out. Use your hands to twist off the full cluster of mushrooms. It should come off in one clump and not leave any stalks behind.
You did it!!! Now enjoy your fresh, homegrown mushrooms.
Flushes
There’s more!?! Yes! Mushrooms will produce a second and even a third harvest. Cover again with damp kitchen roll and repeat as above.
The harvests will reduce with each flush.
I’m showing you how to grow mushrooms so you can use them in your own cooking. Try my Goats Cheese Sourdough Toast with Herby Mushrooms or Slow Cooked Beef and Mushroom Pie
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Thanks,
Lee 🍄
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