I enjoy experimenting with growing things, and this year we tried growing mushrooms. Two different family members bought me growing kits for Christmas, and I’ve enjoyed the pink oyster and chestnut mushrooms we’ve grown. As my current mushroom farms come to the end of their run, I’ve been looking up where to get some new spawn. And this time I may grow them on coffee grounds.
Growing mushrooms on coffee is a highly productive synergy, available for home growing and also done commercially. The reason is pretty simple – the mushrooms respond well to the caffeine. It gives them a massive boost and dramatically accelerates the time it takes to take a fungi culture to fruiting. At the same time, it takes a waste product and puts it to good use as a growing medium for a cash crop.
There are two forms of coffee waste that lend themselves to this. The first is out on the coffee farms. There is plenty of waste biomass in the form of prunings, husks, and pulp from processing the beans. The coffee bean itself is at the center of the coffee cherry, and the rest of the fruit is stripped away. Unfortunately this waste fruit pulp can’t be fed to animals, as the caffeine makes them stressed. So it used to be composted or left to rot – until a researcher funded through the Zeri Foundation discovered that it’s perfect for growing mushrooms. Hundreds of coffee farms have opened up a sideline in fungi since, providing them with a valuable second income stream as global coffee prices have fallen.
Even better, once the mushrooms have grown, the coffee substrate can be reused again: the growing process not only strips out the caffeine, but leaves amino acids and other nutrients that make it a valuable animal feed.
The second form of coffee waste that can be used is coffee grounds from cafes. These would normally go in the bin, but there are two reasons why they’re great for mushrooms. There’s the aforementioned caffeine, but the other reason is that they’ve been through boiling water and are therefore sterilised. Other growing materials such as straw have to be sterilised to kill off bacteria before they can be used, but coffee grounds are good to go.
GroCycle is a social enterprise doing this in Exeter. They collect coffee grounds from cafes and then grow mushrooms in their urban farm. These can then be sold locally, in some cases back to the same cafes and restaurants.
You can do this at home too. There are kits you can buy that are based on coffee grounds, including GroCycle’s or those from the Espresso Mushroom Company. Or if you have a local cafe you can tap for grounds (you need to use them fresh), you could do it yourself much cheaper. If you’re serious about it, you can take GroCycle’s online course on the subject, or download their guide. Let me know if you try it!