Bulk Substrates: How to Select the Proper Substrates and Prepare Them

Knowing the right bulk substrate for your needs and how to prepare it is often going to be the deciding factor in whether your cultivation efforts become fruitful.  Selecting the wrong substrate for the job, or cutting corners is one of the leading factors in the failure of bulk grows, especially with new cultivators.

KNOW YOUR MUSHROOM

Different types of mushrooms want different substrates.  P. cubenis for example grow very well on dung based substrates, and coir.  Ganoderma lucidium will grow well on coir and hardwood substrates, but not dung.  Oysters love straw and paper substrates.  As you can see, there are a variety of substrates that are used, and not all of them are interchangeable between species.  Most substrates need to be pasteurized in order to kill hostile microbes while keeping beneficial ones.  Some need to be sterilized all together.  Here is a list of the most common substrates used, and their prep method:

Coir - Pasteurization
Manure (any herbivore) - Pasteurization
Sawdust - Pasteurization or Sterilization
Paper/Cardboard - Pasteurization or Sterilization
Straw - Pasteurization
Wood Chips - Pasteurization or Sterilization


ADDITIVES

Before moving on to pasteurization and sterilization methods, I just want to talk about additives for a moment.  Many people like to add things like gypsum or coffee to their substrates to speed up colonization.  Powdered gypsum should be added in amounts equaling about 10% of the substrate.  While some people swear by coffee, others hate it because it contaminates easily.  If you add used coffee grounds, make sure that they are decaf, and FRESH!  Don't use the grounds that have been sitting around at Starbucks for unknown amounts of time.  If you need to store coffee grounds for later use, freeze them in a plastic bag.  Add coffee in amounts totaling 10% to 15% of substrate volume.  Add your additives before beginning step 1 of the pasteurization/sterilization process.


PASTEURIZATION

Pasteurization is the most commonly used method of preparing bulk substrates since sterilized substrates contaminate easily once exposed to room air.  Straw, coir, and manure are generally only pasteurized instead of sterilized.  Manure contaminates readily if sterilized, but contains many beneficial microbes that will survive the pasteurization process and help protect your mycelium from contaminates.  Pasteurized straw and coir are also naturally resistant to contamination.  Straw is also often used in quantities that make sterilization a daunting task to say the least.

Pasteurization is a simple process.  I will detail 2 processes here, the first is the standard process used if a pressure cooker is not available, or if only a small amount of substrate is needed.  Some people inoculate bulk substrates with crumbled PF Tek cakes to avoid the use of a pressure cooker, though this is a less efficient method than using grain spawn.  The second process was developed by a user at Myco-Tek who cleverly devised a method of making a bulk pasteurizer for preparing large amounts of substrate with ease.

Method 1:  Supplies Needed:

Large stock pot with steam rack and lid
Meat/Candy Thermometer
2mil Plastic Bags
Twist Ties
Tape (2inch wide or better)
Knife

Step 1:  The first step is to bring your substrate to field capacity.  This means that we need to hydrate our substrate (add water) to the point that when we pick up a handful and squeeze it, only a few drops of water drain out.  If you are using straw or wood chips, soak them over night.  For other substrates, add water slowly and mix in well before adding more.  It is much better to have your substrate too dry than too wet.  If you add too much water to your substrate, add more dried substrate to balance it out.

Step 2:  Load your substrate into the plastic bags and tie them off tightly.  Use a piece of tape to reinforce a small section of the bag, and cut a hole large enough for your thermometer to fit in.  Be sure to do this on the upper portion of the bag.  I like to fold the top of the bag over the hole while heating.  Place bags in the pot above the water line, ensuring that you can access the holes for temperature readings later.  the pot will need to be about 1/3 filled with water.

Step 3:  Turn on a medium heat setting and allow the temperature to rise slowly.  Be sure to check the temperature of your substrate periodically.  Ease off on the heat when the temperature reaches 130f.  Start your timer for 90 minutes when the substrate reaches 140f.  Keep the substrate between 140f and 150f during the cook time.

Step 4:  When the cook time is up, remove the bags from the pot and allow them to cool.  Once the temperature is below 90, they are ready for use.

Method 2:  Because I have found no other method even similar to this, I would like to link you to the original guide uploaded by the inventor.  The guide can be found here.

STERILIZATION

Sterilized substrates are rarely used in bulk cultivation.  Sterilized substrates are used for wood loving species more often than any other type.  Sterilization requires a pressure cooker and plastic filter patch bags.

Supplies Needed:

Pressure Cooker
Steam Rack
Filter Patch Bags
Twist Ties
Still Air Box OR Glove Box OR Flowhood

Step 1:  Bring your substrate to field capacity.  This means that we need to hydrate our substrate (add water) to the point that when we pick up a handful and squeeze it, only a few drops of water drain out.  If you are using wood chips, soak them over night.  For other substrates, such as sawdust, add water slowly and mix in well before adding more.  It is much better to have your substrate too dry than too wet.  If you add too much water to your substrate, add more dried substrate to balance it out.

Step 2:  Load your substrate into your bags.  You only want to fill the bags 1/4 to 1/3 full.  Place the bags inside the pressure cooker above the water line.  Do not tie off the bags, fold the excess plastic back and forth over the substrate like an accordion.  Weigh them down.

Step 3:  Heat at 15psi for 120 minutes.  After the cook time is up, remove the pressure cooker from the burner.  When the pressure lock opens, take the pressure cooker to your still air box/glove box/flowhood.

Step 4:  Under sterile conditions, open the pressure cooker, and remove the bags.  If using a still air box/glove box, fold over each corner at the top of the bag, twist tightly, and secure with a twist tie.  Once this is achieved, you may unfold the plastic and allow air in through the filter patch.  Bags are best inoculated via grain to grain transfer, though some species like Ganoderma have done well through liquid culture or agar wedge inoculation.