By Kim Robson:
We vegetarians do love our mushrooms. They’re meaty, filling, and full of vitamins and minerals; but they are also virtually calorie free and add delicious umami to food without the extra salt. Certain mushroom extracts can help stop migraine headaches (in addition to a number of other benefits) and can help with mental illnesses such as obsessive-compulsive disorder. We keep a bottle of Fungi Perfecti’s CordyChi (cordyceps and reishi) in our refrigerator just for headaches. Foraging for wild mushrooms is fun and great exercise in the woods, but there are many people (like me) who are terrified of picking the wrong thing, and poisoning themselves and their family.
The solution? Grow oyster mushrooms at home, using recycled coffee grounds as a medium! Oyster mushrooms are considered the easiest and most forgiving variety for home cultivators. Now, it’s not uncommon to hear that mushrooms are difficult to grow, but that’s due mainly to lack of knowledge and cheap mass market kits with low quality materials. First things first.
Mushroom Biology 101
Technically, mushrooms are the reproductive fruits of a dense network of root-like threads in the earth called mycelium. In the wild, this network of threads spreads out, breaking down nutrients to fuel its growth. But when it runs out of nutrients or falls under some form of environmental stress, it sprouts mushrooms to release its spores to the wind, hoping for a better location.
We can recreate this life cycle and manage crops of mushrooms, but mushroom farming usually relies on extensive pasteurization equipment and climate control, not a realistic option at home.
Normally, oyster mushrooms are grown on freshly cut hardwood logs or shredded straw. Both come with problems for home growing, though: logs can be unreliable and require up to a year for the first harvest, and straw requires pasteurization to kill microorganisms that would compete with the mycelium.
Luckily, the coffee brewing process pasteurizes coffee grounds, and they are full of nutrients that mushrooms love. You’ll also be recycling a hugely wasted resource.
Inoculating the Spawn
You’ll need to order the mushroom spores (called “spawn”) from a vendor like Fungi Perfecti or GroCycle. Adam Sayner of GroCycle recommends a high spawn-to-coffee grounds ratio, about 500 grams of oyster mushroom spawn to each 5-1/2 pounds (2.5 kg) of used grounds. If the mushroom vendor also sells filter patch grow bags, buy one of those, too. They reduce the chance of contamination and provide a perfect growing environment inside the bag. If you can’t find one, use a gallon-size freezer bag, an empty ice cream tub, or a milk carton — thoroughly cleaned out, and with four or five half-centimeter-wide holes cut in the sides.
Go to a coffeehouse and ask if they’ll give you their spent grounds. My local Starbucks keeps a wheelbarrow outside filled with the morning’s fresh grounds for gardeners to take. You’ll need enough to fill your growing container two thirds full. Make sure the grounds are fresh. Weigh 5-1/2 pounds of grounds into a clean mixing bowl. Wash your hands and lower arms thoroughly. Mix the spawn into the grounds, breaking it up and distributing it evenly throughout the coffee. Pour the mixture into the cultivation bag (or container) and close it up tightly.
Store the growing container in a warm and dark spot, where it’s between 64 and 77 degrees Fahrenheit. Good spots could include a cupboard near the oven or under the bed in a heated bedroom. For about three weeks, you’ll see the spawn grow throughout the coffee grounds, turning the whole mixture white by the time it’s fully colonized. The kids can have fun checking on it and watching it grow from day to day.
Fruiting the Mushrooms
After about three weeks, the whole container of mixture should look completely white. Place the mycelium in a spot with plenty of fresh air and a little light — a shaded windowsill is ideal. If you see any small patches of green mold, try adding a little salt to the area: this should kill it while still allowing the mycelium to grow. If the entire bag goes green, however, then it’s a lost cause. A moldy bag can be caused by poor quality spawn, mold spores getting mixed in with the coffee grounds, or poor hygiene. However, if you use high quality spawn, freshly spent grounds, and use good hygiene, chances are you should have a nice bag of white mycelium ready to fruit your homegrown mushrooms.
Cut a two-inch square hole in your container, and spray water into the hole twice daily. You don’t want it to dry out; mushrooms love damp, humid conditions.
After a week or so, tiny little mushrooms should start sprouting. Over the course of a week or so, they will double in size every day. More fun for the kids! When the edges of the caps begin to turn upwards, it’s harvest time! Cut the mushrooms at the base of the stems and get cooking!