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  • Writer's pictureJeremy Wright

Pasteurizing Mushroom Grain Spawn: A Vital Step for Contamination-Free Cultivation


Pasteurization is a method used in mushroom cultivation to create conditions that favor the growth of desired mushroom mycelium while inhibiting the growth of competing microorganisms. Pasteurizing mushroom grain spawn is a less aggressive technique compared to sterilization, making it ideal for species that are more sensitive to high heat. In this guide, we'll delve into the process of pasteurizing mushroom grain spawn and provide you with step-by-step instructions for achieving successful results.

Materials You'll Need

  1. Grain: Choose a high-quality, nutrient-rich grain such as rye, millet, or oats.

  2. Mason Jars or Bags: These containers will hold the pasteurized grain.

  3. Large Pot or Container: To hold and pasteurize the grain. It should have a lid to help maintain consistent heat and humidity.

  4. Thermometer: For monitoring and ensuring the proper temperature during pasteurization.

  5. Water: Sufficient clean water to soak the grain and maintain moisture during the process.

  6. Rubber Gloves and Disinfectant: To maintain a clean and sanitary workspace.

Steps to Pasteurize Mushroom Grain Spawn

  1. Prepare the Grain: Measure the desired amount of grain and rinse it thoroughly to remove dust and debris. Soak the grain in water for around 12-24 hours to hydrate it.

  2. Drain the Grain: After soaking, drain the excess water from the grain. It should be damp but not waterlogged.

  3. Prep the Pasteurization Container: Fill your large pot or container with the damp grain. Make sure it's spread evenly and not packed too tightly.

  4. Heating the Grain: Place the pot on a heat source and heat the grain to around 140-160°F (60-71°C). Use a thermometer to monitor the temperature and maintain it within this range for about 60-90 minutes. This process effectively pasteurizes the grain without completely sterilizing it.

  5. Cooling: After pasteurization, allow the grain to cool down. You can spread it out on a clean surface or in a clean container to speed up the cooling process.

  6. Inoculation: In a clean and sterile environment (such as a laminar flow hood), inoculate the cooled grain with your chosen mushroom mycelium. This can be done using a syringe, agar wedge, or liquid culture.

  7. Sealing and Incubation: Seal the containers with appropriate lids or covers. Place the inoculated containers in a warm, dark, and humid environment to allow the mycelium to colonize the grain.

Tips for Success

  • Maintain Cleanliness: Prioritize hygiene and cleanliness throughout the process. Wash your hands, use gloves, and sanitize all tools and surfaces to minimize contamination risks.

  • Temperature Consistency: Keep a close eye on the temperature during pasteurization. Fluctuations can affect the efficacy of the process.

  • Ideal Mycelium Growth Conditions: After pasteurization and inoculation, maintain proper environmental conditions including temperature, humidity, and air exchange to support optimal mycelium growth.

  • Use Quickly: Pasteurized grain spawn is more prone to contamination than sterilized spawn. Use the spawn within a reasonable time frame to prevent contamination from taking over.


Pasteurizing mushroom grain spawn offers a balance between reducing contamination risks and maintaining favorable conditions for mushroom mycelium growth. By carefully following the steps outlined in this guide and paying attention to detail, you can increase your chances of successfully cultivating mushrooms using pasteurized grain spawn. Remember that practice and patience are key to mastering this technique and enjoying a bountiful harvest of your favorite mushroom species.

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