The cultivation of mushrooms in jars offers an accessible method for home growers to produce their own fungi. This technique, often associated with the PF Tek method, simplifies mycology by utilizing small, ready-to-handle substrate containers. Containing the growing medium within glass jars significantly reduces the risk of widespread contamination, making it suitable for beginners. This approach involves precise steps, from preparing the nutrient-rich substrate to creating the high-humidity environment necessary for development. Following a structured process ensures the creation of a sterile environment, which is the foundation for a successful harvest.
Required Supplies and Substrate Preparation
The first step involves gathering materials and preparing the growth medium, or substrate, within the jars. Supplies include half-pint or pint-sized wide-mouth canning jars, a pressure cooker for sterilization, and tools for inoculation such as a spore syringe. The primary components of the substrate are brown rice flour (BRF), vermiculite, and water, which provide the necessary nutrients and moisture retention.
The standard ratio is two parts vermiculite, one part BRF, and one part water, measured by volume. Vermiculite is first mixed with water until it reaches “field capacity”—moist but with no excess water pooling. The brown rice flour is then gently folded into the wet vermiculite, creating a light medium that provides carbohydrates for the developing mycelium.
The substrate is lightly spooned into the jars, filling them up to the shoulder without compression. Packing the medium too tightly restricts the air pockets necessary for the mycelium to colonize efficiently. A final, dry layer of vermiculite, about half an inch thick, is added on top. This dry layer serves as a contamination barrier, preventing airborne contaminants from reaching the nutrient-rich substrate after sterilization.
Sterilization and Inoculation Procedures
Sterilization eliminates all competing organisms, ensuring the mycelium has a clean environment for growth. After filling, the lids are prepared with inoculation holes—typically four small holes—and covered loosely with aluminum foil. The jars are then placed into a pressure cooker, elevated above water using a rack to prevent direct heat contact.
For effective sterilization, the pressure cooker must reach 15 PSI (250°F/121°C). This temperature is required to destroy heat-resistant bacterial endospores and fungal contaminants. The jars are sterilized at this pressure for a minimum of 90 minutes. Afterward, the heat is turned off, and the cooker must be allowed to cool naturally and completely to prevent the sudden pressure drop from shattering the jars.
Inoculation, where the culture is introduced, must be performed using strict aseptic technique to maintain sterility. This involves working in a still, clean environment, often using 70% isopropyl alcohol. A spore or liquid culture syringe is used to inject solution through the lid holes into the substrate, typically in four locations. After injection, the holes are sealed with micropore tape to allow gas exchange while filtering out airborne contaminants.
Colonization and Environmental Monitoring
Following inoculation, the jars enter the colonization phase, where the thread-like mycelium network spreads throughout the substrate. This growth requires a stable, warm environment, typically in a dark location, as light is not needed at this stage. The ideal temperature range for rapid colonization is between 70°F and 78°F; temperatures outside this range slow growth or increase contamination risk.
Growers should monitor the jars daily, looking for white, cottony growth radiating from the inoculation points. This white network is the healthy mycelium consuming the nutrients. Colonization is complete when the white growth fully envelops the entire substrate mass, which usually takes two to four weeks.
Discoloration, such as green, black, or pink patches, indicates contamination by mold or bacteria. Green mold, often Trichoderma, is a common contaminant requiring immediate isolation or disposal to prevent spore spread. The health of the mycelium is confirmed when the entire substrate, referred to as a “cake,” appears solid white and firm.
Setting Up the Fruiting Environment and Harvesting
Once the substrate cakes are fully colonized and firm, they are removed from the jars and transferred to a dedicated fruiting environment. The goal of the fruiting chamber is to provide the high humidity, fresh air exchange (FAE), and light required to trigger the formation of mushroom pins. A common setup is the Shotgun Fruiting Chamber (SGFC), a plastic container with numerous small holes drilled into all sides, including the lid and bottom.
The SGFC uses a 2 to 3-inch layer of moistened perlite, an expanded volcanic glass, on the bottom. Perlite retains and releases moisture, maintaining the high humidity levels (85% to 95%) required for fruiting. Before placement, the cakes should be soaked in clean water for several hours—known as “dunking”—to rehydrate the substrate. They are then rolled in dry vermiculite to create a moist, protective outer layer.
Maintaining the chamber involves regular misting of the perlite and walls, avoiding direct contact with the mushrooms. Fanning the chamber several times a day is necessary to prevent carbon dioxide buildup, which inhibits development and causes spindly stems. Mushrooms are ready for harvest just as the veil, the membrane beneath the cap, begins to tear. Harvesting at this stage maximizes potency and prevents spore release, which can signal the cake to stop producing further flushes.