Mycelium is the vegetative body of a fungus, a vast, root-like network of branching filaments called hyphae. This structure acts as the fungus’s digestive system, extending through soil, wood, or grain to break down and absorb nutrients. In nature, mycelium is the primary recycler, decomposing organic matter to enrich the ecosystem. Cultivating this network allows for the production of mushrooms and sustainable bio-materials. The process requires a meticulous approach focused on cleanliness and environmental control.
Essential Materials and Sterile Setup
Successful cultivation requires establishing a clean workspace and gathering specialized equipment. Maintaining sterility is the most important element to prevent the growth of molds and bacteria. Essential tools include glass jars or specialized bags for the growth medium, which must be rated for high-pressure heat treatment. A pressure cooker or autoclave is necessary to achieve the temperatures needed for true sterilization.
The transfer of fungal culture must occur in a strictly controlled environment. Small-scale cultivators often use a still air box (SAB), a sealed container with arm holes designed to minimize air movement and airborne contaminants. Larger operations use a laminar flow hood, which provides a continuous stream of filtered, sterile air. Personal protective equipment, such as nitrile gloves, face masks, and hairnets, must be used to prevent contamination from the cultivator. An inoculation loop, scalpel, or sterile syringe is required for the precise introduction of the fungal culture.
Preparing the Growth Substrate
The substrate serves as the food source for the growing mycelium and requires careful preparation to eliminate competing organisms. The decontamination method depends primarily on the substrate’s nutrient density.
Sterilization
Nutrient-rich materials like grain (e.g., rye or millet) are prone to contamination and require sterilization, which eliminates all living organisms, including bacterial endospores. Sterilization is achieved by treating the substrate in a pressure cooker at 250°F (121°C) and 15 PSI for approximately two hours for small jars, or up to three hours for larger bags.
Pasteurization
Bulk substrates like straw, wood chips, or sawdust are often prepared using pasteurization. This process involves heating the medium to a lower temperature, typically between 149°F and 167°F (65°C and 75°C), and maintaining it for one to two hours. Pasteurization kills most competing molds and bacteria but intentionally leaves behind certain heat-tolerant, beneficial microorganisms. These remaining microbes inhibit the growth of more aggressive contaminants. The substrate must cool completely to room temperature before the fungal culture is introduced; otherwise, the heat will destroy the mycelial tissue.
Transferring the Fungal Culture
Once the substrate has cooled, the fungal culture is introduced in a process known as inoculation, performed within the sterile workspace. The culture is typically transferred using one of three common forms: liquid culture, spore solution, or an agar wedge.
Liquid culture, which is active mycelium suspended in a nutrient broth, provides a fast-acting inoculum often injected directly into the sterilized grain jar using a sterile syringe. Spore solutions are easier to prepare but require a longer initial germination phase and carry a higher risk of contamination.
Using an agar wedge involves cutting a small piece of actively growing mycelium from a petri dish and transferring it to the substrate. This method is favored because the cultivator can visually confirm the absence of contamination on the agar before the transfer. Every tool that contacts the culture or the substrate must be sterilized, often by briefly heating metal tools with a flame and allowing them to cool. The culture is then placed carefully into the prepared substrate, and the container is immediately sealed.
Monitoring Mycelium Development
After inoculation, the containers are moved to a dark incubation area to allow the mycelium to fully colonize the substrate. The speed and health of colonization depend on maintaining a consistent temperature, generally within the range of 70°F to 80°F (21°C to 27°C) for most cultivated species. Temperatures outside this range can slow growth or promote the proliferation of contaminants.
The mycelium typically begins to spread and become visibly apparent within five to seven days, appearing as fine, white, thread-like growth radiating from the inoculation point. Full colonization, where the entire substrate is bound by a dense, white mycelial mat, usually takes between two and four weeks, depending on the species and the substrate volume. Cultivators must constantly monitor the containers for signs of contamination, which often present as patches of green, blue, black, or pink mold, or a sour odor. Any container showing these off-colors should be immediately isolated and removed to protect the healthy batches.