I did an intense technical ( one to one mainly ) course of study to become the assistant production manager at a fairly large mushroom farm enterprise back in the early 1980's .
I was just going to start the typing when on a whim I put, " Making mushroom compost " into Google this link came up ..saves me typing for an hour or so ..it is ideal .
http://www.food-from-the-garden.com/mushroom-compost.html Give me a few more minutes & I hope to come back with on line words about making the capping / casing and getting it sterile
Well I never ..found this ..it's self explanatory , it is a fairly definitive guide for small commercial production .
http://mushroominfo.com/growing-mushrooms/six-steps-to-mushroom-farming/ If you can follow this you're in business .. To pasteurize the casing use a ( top cut off) 45 gallon oil drum 1/3 filled with water on a tar burner gas ring ( set the barrel on concrete blocks and make a wind break so the heat works on the barrel and does not get blown away . .
Suspend the fine sieved capping loam in hessian or poly prop sacks ( sand bags ??) just above the water. Once it starts boiling cover the drum with some sort of lid to keep the heat in & let it simmer for 4 hrs. , keep an eye on things in case you need to top up the water ..total sterilization time must be 4 hrs or more over the boiling water to pasteurize it.
We had a massive diesel fired electric driven Wicks steam generator that fed a large 12 x 8 foot wide 2 foot deep tarpaulin covered perforated pasteurizing bed full of fine sieved capping loam .)
I/4 fill the black sacks with the finished mushroom compost , press it down faailry firmly , crumble some spawn over the top 1/2 teaspoon full per bag add one inch of pasteurized capping , close bag by folding the top over place in a warm place that has a reasonable air flow . If you have a dark room you can use clear heavy duty new poly bags .
Just make sure that whatever you use you can pick up a bag easily as they weigh about three stone when newly made up.
Keep cats out the area as they love to pee on the bags and any forming mush rooms .( guess how I know
)
Depending on the temp depends on when to expect the mushrooms.
To prolong the harvest of mushrooms after you have picked the first flush always replace any disturbed capping and when it seems no more are going to grow use a fine rose watering can to spray a solution of half an ounce of cooking salt per gallon of warm water over the cappings . It causes the compost to break down further and also helps kickstart the second growth ..sometimes you can even get a third growth using the salt trick.
NOTE WELL
I recommend you use a brand new watering can and rose for the salt solution so that you are 100 % sure there is no chemical contamination in the can as the minutest amounts of all sorts of garden chemicals will kill mushroom spawn/spores .