Sterilize the canning jars. You can do this by running them through a dishwasher cycle. Wash your hands with antibacterial soap before removing and working with the jars or working on your mushroom growing project.
Place the vermiculite into a large mixing bowl. Pour in water, a little at a time, allowing the vermiculite to absorb it. Use mineral or bottled drinking water, if your tap water has chlorine or other chemicals. Stir the mixture with a spoon. When the vermiculite stops absorbing, you have enough water. Pour out any excess water.
Mix the brown rice flour into the bowl to coat the vermiculite.
Fill each sterilized jar with the vermiculite mixture, up to a half-inch from the top. Do not tap the jar to compact the mixture; it must remain loose and airy. Clean off the rim of the jar with a cloth. Add dry vermiculite until the jar is full to the top.
Cover the jars with three layers of aluminum foil. Make a lid by wrapping the first two layers around the lip of the jar. The last layer should be large enough to go down the sides about 2 inches. Fold and crease the sides of the foil, so it fits snugly to the jar sides.
Place the jars onto a rack in a pressure cooker or canning pot. Add water to the pot until it reaches about an inch below the tops of the jars. Cover the pot and cook over medium heat. When steam starts to escape, turn the heat to medium-low and leave it for about 45 minutes (1½ hours in canning pot) . Remove the pot from the stove and let get cool to the touch. Remove the jars.
Shake up the syringe of mushroom spores that came with your kit. This will break up the clumps of spores. Sterilize the needle tip with a flame.
Remove the top piece of foil from each jar. With a sterile knife, pierce four small holes in each jar through the remaining two pieces of foil. Using the syringe, drip a small amount of the spores onto each jar in four different areas. Re-sterilize the needle tip before moving on to the next jar. Replace the large aluminum sheets over the tops of the jars and wrap them tightly around the jar sides.
Keep your jars in a very warm, dark location, between 70 and 80 degrees F. Germination should take place in three to five days. Within 14 to 28 days, you sould see colonization, when the whole jar sides look white. Then the temperature can be a bit cooler, normal room temperature. You may use a low-wattage lamp in the room for up to 12 hours a day. This will enable you to see your way around. This is handy if the room is also used for other purposes.
When you start to notice small mushroom heads on the sides of the jars, you can start the fruiting process. Put a wet paper towel at the bottom of a plastic bucket or other plastic container. The container size is not important. Placing a jar upside-down, close to the bottom of the container, and pour out the contents. Continue to empty the jars, keeping the contents of each separated by about 2 inches. Use additional containers if needed. Cover the containers with plastic wrap, still keeping them out of direct light. The mushrooms will begin to grow. They can be harvested as soon as the heads begin to open.