Pasteurizing straw for growing mushrooms can be done in several ways; either by using the conventional method which involves pasteurization or the cold method which involves using a hydrated lime bath.
Substrate is the medium on which the cultivated mycelium grows and Straw is a fine substrate for the commercial growth of many varieties of mushroom, because it provides the necessary cellulose base for fruiting. But it must be properly prepared for mycelia growth since it is prone to green molds.
That’s what makes pasteurization very crucial to the whole process and it has to be done before inoculating with the mushroom spawn.
Sometimes, even with proper pasteurization, straw will naturally begin to contaminate with molds within two weeks if not fully colonized (because of competition from other organisms).
Therefore, it’s equally important to only use aggressive, fast colonizing species/strains with straw, and to provide the correct conditions for colonization so that the project is fully colonized within the 2-week time frame you have available.
Pasteurizing Straw for Growing Mushrooms is done in stages
Straw must first be chopped and hydrated. Chop the straw into pieces to break the waterproof coating on the straw and enable it to absorb water, providing a better medium for the mycelium to grow.
It will be worth investing in a chopper if you’re doing a large quantity of straw but if you’re growing at home, you can place the broken up (from the bale) straw into a clean trashcan or any other container, and then go at it with your weed eater. Other growers might lay it on the driveway or yard and use the lawnmower. But really, any method you devise to get the straw chopped up will be fine.
In step two:
Hydrate the chopped straw in a container of warm water. The warm water is optional, but I’ve found the warm water hydrates the straw faster. Push the straw into the warm water and agitate it with your hands to work up. Allow it to sit for two to four hours.
Pasteurization straw fro growing mushrooms is the most critical step in the whole process. The grower “must”pay close attention to the time and temperature.
Pasteurization can be done in a 55-gallon steel drum and a simple heat source for the drum can either be a propane weed burner focused on the bottom of the barrel, or Cast iron camp stove, or even firewood.
First, pack the straw into a large burlap bag or a wire mesh basket made from hardware cloth. Then heat the water in the drum to 160° -170°.
After the water has reached 160° to 170°, place the filled bag or basket in the water. After about 15 minutes, turn off the heat. Leave immersed for about 30 minutes more, then remove and drain for 10 to 15 minutes.
Allow to cool by placing the pasteurized straw into a mixing container to finish cooling. Once cool, it’s ready for spawning.
Spawning must be done in a clean room to avoid contamination. A proper mix should have the dry weight of the substrate calculated, and add 10% of that weight in spawn added.
Now mix the spawn into the cooled straw. Mix the spawn into the substrate until evenly distributed. Fill the inoculated straw tightly into clear plastic bags (or tubes for larger quantities).
Be sure to package it tightly, then tie the top off with a wire tie, or fold the top over and use packing tape to create a seal.
Note: It doesn’t have to be air tight, as the bag should be no smaller than about the size of a gallon jar. Tubes can be created using plastic tubing up to 16 inches in diameter and 8 feet long.
Punch needle holes right after bagging to allow for adequate aeration. It is advisable to let the mixture breathe otherwise, it will go anaerobic and the spawn may die or the straw will go sour.2