So you've probably heard about this "new" method of growing mushrooms, using spent coffee grounds. Seems like a great idea, just add some spawn to used coffee grounds and harvest loads of mushrooms!
This is not a new technique, it has been around for over a decade. Several companies in the USA, UK and Europe have used crowdfunding to start up Oyster mushroom growing enterprises, using coffee grounds. There are also a few Australian startups cashing in on the trend. You can check out how similar some of these enterprises are http://grocycle.com/ and https://lifecykel.com.au/ .
The process is made to appear simple, just add spawn to the collected coffee grounds. The reality is very different. If you look closely at the bags that produce mushrooms, you may be able to see there is straw in the bags. So the coffee grounds only make up a small % of the actual substrate in the bags. And the coffee usually needs to be treated again, after collection, to prevent contamination. These facts are conveniently left out, to make the process more appealing to donors and customers.
We've been growing using coffee grounds for years, but only as a supplement. So can you use just untreated coffee grounds to grow gourmet mushrooms? Well, yes, you can, but the results aren't great, because coffee grounds spoil quickly, they hold a lot of moisture, and their small size makes it difficult for mycelium to navigate. So most growers mix the coffee grounds with straw and/or sawdust and lime or gypsum, then bag it up and heat treat it, before they add spawn.
We have consulted with the owners of some of these urban farms, and wish them the best of luck-in fact, students of our mushroom growing courses now supply spawn to 2 of the Australian startups.
We're teaming up with some local Tasmanians to start turning some of Tassies coffee waste and spent brewery waste into locally grown Tasmanian mushrooms. If you would like to be a part of this new social enterprise, follow us on Facebook for updates.