Sterilisation Techniques for Mushroom Cultivation: Tools, Methods, and Tips

Sterilization is one of the most important steps in growing mushrooms, especially when using nutrient-dense substrates like grains. If proper sterilization isn’t achieved, contaminants like molds or bacteria can outcompete the mycelium and ruin the entire crop.

1. Pressure Cooker Sterilization

How to Use a Pressure Cooker:

• Preparation: Fill your jars with hydrated grain or substrate and cover with foil to keep moisture out.

• Pressure Cooking: Place the jars in the pressure cooker with 3-4 cm of water at the bottom. Heat until it reaches 15 PSI and maintain it for 90 minutes.

• Temperature and Pressure: At 121°C, the high pressure ensures that even heat-resistant spores are destroyed.

Tools Needed:

• Pressure Cooker: Ideally one that can reach 15 PSI.

• Jars with Lids: Mason jars are perfect for holding the substrate and allow for easy inoculation.

2. Pasteurization

What is Pasteurization?

• Pasteurization involves heating the substrate to a point where harmful microorganisms are killed, but beneficial bacteria that aid mycelium growth are preserved.

How to Pasteurize Straw:

• Water Bath: Cut straw into pieces around 3-5 cm long and immerse in hot water between 65-80°C. Keep the straw submerged for 60-90 minutes.

• Drain: After pasteurization, allow the straw to cool and drain thoroughly before inoculating it with grain spawn.

Best Substrates for Pasteurization:

• Straw, sawdust, and manure are common substrates that benefit from pasteurization rather than sterilization.

3. Chemical Sterilization

Chemical sterilization is generally used when there isn’t access to a pressure cooker, though it’s not as effective for substrates like grains. Hydrogen peroxide (3%) can be used for cleaning tools and working surfaces, while hydrated lime is sometimes used to pasteurize straw.

Common Sterilization Tools and Safety Tips:

• Alcohol Spray Bottle (70% Isopropyl Alcohol): Use to clean tools, surfaces, and gloves during inoculation.

• Laminar Flow Hood or Still Air Box (SAB): Creating a sterile workspace is as crucial as sterilizing substrates. A flow hood helps to push out contaminants, while an SAB keeps air still to minimize airborne spores.

• Heat-resistant Gloves: Handling jars from a pressure cooker can be challenging without good gloves.

Proper sterilization is crucial to prevent unwanted bacteria or mold from competing with the mycelium. Whether using a pressure cooker for grains or a hot water bath for straw, proper preparation and tools make all the difference in growing healthy mushrooms.