How To Sterilize Grains With Pressure Cooker & Mushroom Grow Bags

Sterilizing grain bags is a crucial step in mushroom cultivation to ensure a contamination-free environment for your mycelium to grow. Using a pressure cooker is a common method for achieving proper sterilization. Here's a detailed guide on how to sterilize grain bags using a pressure cooker:

Materials and Equipment You'll Need:

  1. Grain bags filled with your chosen pre-soaked substrate (e.g., rye berries, millet, etc.)
  2. Pressure cooker (Make sure it's clean and in good working condition.)
  3. Water
  4. Heat-resistant gloves
  5. Timer
  6. Rack to elevate the bags above the water



  1. Prep your Grain Bags:

    • Fill your grow bags with the chosen pre-soaked substrate. Make sure you've measured and mixed the substrate properly according to your mushroom cultivation recipe.
    • To seal the bags, fold the top flap of each bag against the grains inside. This creates a double layer of plastic that helps prevent water from entering the bag during sterilization.
  2. Add Water to the Pressure Cooker:

    • Fill the pressure cooker with an appropriate amount of water. Usually, around 2-3 inches (5-7 cm) of water is sufficient. Follow your pressure cooker's manual for guidance.
    • Place a rack or a towel at the bottom of the pressure cooker. This will prevent the bags from coming into direct contact with the hot surface, preventing scorching.
  3. Load the Pressure Cooker:

    • Place the folded grain bags on the rack or towel inside the pressure cooker. Make sure there's space between the bags for steam to circulate.
    • Don't overcrowd the pressure cooker. Depending on its size, you may need to sterilize the bags in batches.
  4. Seal and Prepare the Pressure Cooker:

    • Ensure the pressure cooker's rubber gasket is clean and in good condition.
    • Place the lid on the pressure cooker and lock it securely.
    • Double-check that the pressure release valve is closed.
  5. Heat Sterilization:

    • Place the pressure cooker on a stove burner set to medium-high heat.
    • Allow the pressure to build up inside the cooker until the pressure release valve pops up or steam starts escaping steadily. This indicates that the pressure cooker is pressurized.
    • Start your timer for 3 hours once the pressure is achieved. Maintain the pressure at 15 psi (pounds per square inch) throughout the entire sterilization process.
  6. Sterilization Time:

    • Sterilize the bags for the entire 3-hour duration, maintaining the pressure at 15 psi. This extended time and pressure are crucial for thorough sterilization and preventing contamination.
  7. Cooling and Removal:

    • Once the 3-hour sterilization time is complete, turn off the heat and allow the pressure cooker to cool down naturally. Do not rush this step.
    • Once the pressure has completely dropped and it's safe to open the pressure cooker, carefully remove the sterilized bags using heat-resistant gloves.
  8. Sealing and Storage:

    • After the cooling process, the folded bags will have a hermetic seal; however, for an additional safety precaution, you can choose to heat seal them.
      • Gently heat seal the upper section of the bag's flap without compromising the existing hermetic seal.
    • Store the sterilized bags in a clean and controlled environment until they're ready for inoculation with mushroom spores or mycelium.

Maintain strict hygiene and cleanliness throughout the process to prevent contamination. Always adhere to safety guidelines for using pressure cookers to ensure a safe and successful mushroom cultivation journey.