how to make grain spawn jar lids

Creating grain spawn jar lids is an essential part of the process if you’re planning to grow mushrooms using the grain-to-grain transfer or agar-to-grain methods. These lids allow for the inoculation of sterilized grain with mushroom mycelium. Here’s how to make grain spawn jar lids:

Materials You’ll Need:

  1. Metal canning jar lids with a rubber gasket (the kind used for canning or preserving food)
  2. Drill with a 14-inch or 38-inch drill bit
  3. High-temperature resistant filter material (polyfil, synthetic filter discs, or tyvek)
  4. Self-healing injection ports (optional but recommended)
  5. Silicone sealant or high-temperature adhesive (like RTV silicone)
  6. Alcohol and a cloth or paper towels for cleaning
  7. Scalpel or utility knife
  8. Pressure cooker or autoclave for sterilization


  1. Prepare Your Workspace:
    • Ensure that your work area is clean and free from contaminants. You’ll be handling materials that need to be sterile to prevent contamination during the mushroom cultivation process.
  2. Clean the Lids:
    • Clean the metal canning jar lids thoroughly with soap and water. Rinse them well to remove any residue.
    • Wipe them down with alcohol and a clean cloth or paper towel to sterilize the surface.
  3. Drill Holes for Inoculation:
    • Using the drill with a 14-inch or 38-inch drill bit, create a hole in the center of each lid. This hole will be used for inoculation.
    • If you’re using self-healing injection ports, drill additional holes around the center hole to accommodate them. These ports make it easier to inject spore syringes or liquid culture into the jars.
  4. Attach Filter Material:
    • Cut a piece of high-temperature resistant filter material (polyfil, synthetic filter disc, or tyvek) into a circle slightly larger than the lid.
    • Place the filter material over the lid, covering the drilled holes.
    • Secure it in place with the lid ring.
  5. Add Self-Healing Injection Ports (Optional):
    • If you’re using self-healing injection ports, attach them to the additional holes you drilled. These ports allow for easy and sterile inoculation.
    • Secure them in place with silicone sealant or high-temperature adhesive. Allow the adhesive to dry thoroughly before use.
  6. Seal the Filter Material:
    • Apply a bead of silicone sealant or high-temperature adhesive around the edges of the filter material, sealing it securely to the lid.
    • Ensure there are no gaps or openings where contaminants could enter.
  7. Allow the Adhesive to Cure:
    • Let the silicone sealant or adhesive cure for the recommended time, which is typically 24 hours.
  8. Sterilize the Lids:
    • Prior to using the lids, sterilize them in a pressure cooker or autoclave to ensure they are free from contaminants.

Once your grain spawn jar lids are prepared and sterilized, you can use them for inoculating sterilized grain jars with mushroom mycelium. Be sure to follow proper sterile procedures during this process to avoid contamination and achieve successful mushroom cultivation.

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