Several strains of specialty mushrooms can be grown on pasteurized straw, including several types of oysters, the black poplar mushroom and some strains of shiitake. Straw cultivation can be the easiest and cheapest method to get new growers started due to the easy, low-tech methods that are often used. Using only a 55-gallon drum, a mesh basket to fit the drum, a propane burner, an easily cleaned table (preferably stainless steel), some grain spawn, and a growing facility.
Typically, a 55 gal drum is filled ¾ full with water and heated by a burner attached to a propane tank, or the straw is placed in an unpressurized steam chamber. When using a drum, usually a basket made of ¼" hardware cloth is constructed to fit inside the drum. When using a steam chamber, the straw is placed in baskets that are set in to the chamber. It is ideal to use chopped straw that is between 1" to 4" in length, but this is not absolutely necessary. The straw can be chopped with a garden shredder, a bale shredder or a tractor attachment shredder. The straw is then stuffed into the basket. Once the water has begun to boil, the straw is placed into the water and pasteurized for 1 hour. During this time, the water is maintained at a slight boil. Pasteurization will eliminate all insect life, living fungi and most types of bacteria. Many spores and heat-tolerant bacteria will survive. Heat-tolerant bacteria tend to have a beneficial relationship with many types of mushrooms, especially the king stropharia which grows poorly in their absence.
Once an hour has passed, raise the basket out of the water and allow it to drain into the drum for ten minutes. This can be done by simply placing two 2" x 4" 's on top of the drum to rest the basket on. The straw is then spread out on a clean table and allowed to cool.
Once the straw is cool, it is inoculated with grain spawn by simply mixing the spawn evenly into the straw. One basket of pasteurized straw usually weighs about 60lbs. The straw must be inoculated with an adequate amount of spawn to insure that the straw will be colonized within 7 to 10 days. If the straw is not colonized within that time period, spores that survived pasteurization might germinate and contaminate the straw. Some growers inoculate at a low rate of one 5 lb bag of grain spawn to 160 lbs of pastuerized straw, which can fill four bags with a height of 4' and a diameter of 12". A heavier inoculation rate of one 5 lb bag of grain spawn to one 40 lb straw bag, usually results in much lower contamination rates and significantly higher yields. The inoculated straw is stuffed into plastic bags that will either be hung from the ceiling or that will rest on a support. The bags must be packed tightly so that the straw will be pressed up against the plastic bag. If the bags are to hang in the air, they must have a thickness of 4 mil. Typically, cylindrical bags with a 12" diameter and a length of 4' to 12' are used. A 4' bag with a diameter of 12" weighs between 40 lbs. to 50 lbs. when filled with inoculated straw.
After the filled bags are placed into the growroom, holes are punched into the plastic. These holes can be made by using a four-sided stainless steel arrowhead. If you only have access to knife, these holes can be mad by cutting slits ½" in length in the bag with a knife. Cut one ½" slit across the bag horizontally, then cut another ½" slit vertically through the middle of the horizontal slit. About 25 of these holes are needed in a 4' bag with a spacing of 4" to 6" between the holes.
The water used for pasteurization can be used two more times before it must be changed. This greatly decreases the cost of producing the bags, since the water will already be hot and less propane will be used. Right after the pasteurized straw is emptied on to the table, the next load of straw can be stuffed into the basket and placed into the drum. After using the water three times, the concentration of toxic substances in the water becomes too high. If this water is used a fourth time, the growth of the oyster fungus will be inhibited.