We need to soften the grains-this is done by soaking in water, and/or cooking them. You’re after the same consistency as cooked brown rice. The longer you soak them in water, the less you have to cook them prior to sterilizing. If you soak for 48hours or longer, there is usually no need to soften them further by cooking.
Gypsum can be added now, at 5-10% of the dry weight of the grains. I sprinkle the gypsum straight on top of the grains, then mix in by hand. Gypsum provides calcium and sulphur, and also helps stop the grains from sticking together.
Grains for spawn production are usually sterilized, using heat. A pressure cooker comes in handy for this, as they can reach over 120 degrees Celsius, and efficiently sterilize. The softened grains are loaded into bags or jars, leaving room for the spawn you will later add. Pressure cook for 2 hours at 15psi. Allow at least 6 hours for you grains to cool prior to inoculating with spawn.
A Microwave ( I zap bags at full power for 20 minutes, 3 times, 12 hours apart) or big pot with a lid (simmer for 6 hours) will also work, but not as efficiently.
Milo: No, not the chocolate powder drink (although that’s useful with agar for Petri dishes).This is a useful grain, being cheaper than most, and as good as any I’ve used. It can be hard to find certified organic Milo.
Popcorn and Maize: These are closely related grains, with similar properties. Popcorn is usually somewhat cleaner.
Wheat: I’ve had good results with wheat, however it does tend to contaminate more so than the other grains I’ve used. To combat this, I soak the grains for at least 48 hours, which allows the endogenous micro-organisms to germinate prior to sterilizing. The fermentation process softens the grains, and the nutritional content changes. The Pleurotus species are actually omnivorous, killing various insects, as well as other micro-organisms, in order to obtain the nutrients they need.
Oats: Much like wheat, less prone to contamination. Preferred by Shiitake.
Wild Bird Seed: Sometimes cheaper than the other grains, although rarely certified organic. A good rinse prior to soaking is recommended, and remove any floaters.
Sometimes grains can be a bit dirty, with various sorts of plant matter, spoiled grains, bacteria and fungal spores. One method that has shown good results with dirty grain is to add 5L of dry grains to a 9L bucket, then add 1-2 tablespoons of “Aware” clothes washing powder (a mix of plant oil surfactants, cellulose colloids, mineral zeolite, salts and limestone) then top up with water to the 9L mark. The washing powder kills lots of harmful micro-organsims, and is actually food for your mushrooms, 100% biodegradable and non-toxic. After a 24-48 hour soak, drain (rinsing is optional), and load into bags/jars. Then cook in your Pressure Cooker for 2hours at 15psi.
If you don’t have a PC you can Microwave several batches for 20 minutes at full power, leave for 12-48 hours, then give them another 20 minutes. Alternatively, you can use a big pot with a lid (like a Vacola), and steam the bags/jars for 6 hours ( or for 3 hours, rest for 24 hours, then steam again for 3 hours). This process is a form of Tyndallisation.
Once sterilized, your grains are ready to be inoculated. This is best done in a glove box ( a still air environment), or in front of a laminar flow hood. If you don't have either of those, work quickly in a clean room.
Here are some of my early glove boxes-they worked wonderfully. These are, in effect, laboratories.
Those plastic boxes are dangerous to cut with a knife, so I heated up an old tin can, and melted the holes.
To clean your glove box, spray the insides with 10% bleach, 90% water.
The carboard box just had glad wrap over the front, and I would lift the wrap up just enough to get my hands in. The plastic box had the top covered in glad wrap, because it was more transparent than the original lid.
Everything that goes in the box should be clean. I use 70% metho with 30 % water to spray the outside of the spawn bags, any knives, and my hands just prior to putting them in the box.
A tiny piece of mycelium is capable of colonizing a whole bag, but the more mycelium you add, the faster the bag will colonize, and contamination will be less likely. I usually make 5 new bags from 1 old bag.