Michael Davis
Building a mushroom sterilizer is a complex process that requires careful planning and execution. The goal of sterilization is to kill contaminants and pathogens that can affect mushroom growth. This can be achieved through various methods, including pressure cooking, pasteurization, and atmospheric sterilization. One popular method involves using a drum sterilizer, which utilizes steam and heat to sterilize the substrate. Building a drum sterilizer requires materials such as barrels, insulation, temperature controllers, and valves for controlled steam release. Safety considerations, such as preventing pressurization and limescale buildup, are crucial. Proper ventilation and vacuum cycles are also essential to ensure effective sterilization and prevent contamination during the cooling process. The design and construction of a mushroom sterilizer involve a careful balance of steam, pressure, time, and temperature to create optimal conditions for mushroom cultivation.
| Characteristics | Values |
|---|---|
| Purpose | To sterilize mushroom substrate |
| Sterilization method | Atmospheric, steam, pressure cooking |
| Temperature | 70°C, 91°C, 121°C, 150°C |
| Time | 8-12 hours |
| Equipment | Barrel, boiler, drum, pressure cooker, autoclave, PID controller, temperature controller, ball valve, hosepipe, exhaust port, insulation, rolling racks, water spray, air filter, thermocouples, low-pressure boiler, propane tank |
| Materials | Stainless steel, ceramic-coated drum, neoprene sheeting, aluminium tape, radiator reflection foil, Kingspan insulation, rockwool |
| Safety considerations | Preventing limescale and rust, controlling steam, avoiding bag inflation and barrel pressurization, thermal fuse, water overflow circuit |
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What You'll Learn
Choosing a design: single-drum or double-drum atmospheric sterilisers
When it comes to choosing a design for your mushroom sterilizer, you have the option of a single-drum or a double-drum atmospheric sterilizer. Here are some considerations to help you decide:
Single-Drum Atmospheric Sterilizer:
Eric Myers has designed a single-drum atmospheric sterilizer that optimizes space and eliminates heat loss. His design incorporates the heating element inside the drum, which also allows for automation. This design is straightforward and effective, making it a popular choice for those building their own mushroom sterilizers.
Double-Drum Atmospheric Sterilizer:
For larger-scale operations, a double-drum sterilizer might be more suitable. Marc R. Keith has designed a 55-gallon drum steam boiler sterilizer with two modules: one boiler and one for loading bags. This design is often used by mushroom farms, such as Mossy Creek Mushrooms, to heat and moisten the air continuously. The double-drum design ensures that sterilization is more efficient and effective, especially when paired with steam.
Factors to Consider:
- Space: The single-drum design is more compact and space-efficient, making it ideal for smaller spaces or home setups.
- Heat Loss: The single-drum design eliminates heat loss, making it more energy-efficient.
- Automation: The single-drum design allows for automation, which can save time and effort.
- Scale: If you plan to sterilize a large volume, a double-drum design might be more suitable to handle the workload.
- Continuous Operation: The double-drum design is often paired with steam to heat and moisten the air continuously, making it ideal for uninterrupted operations.
Ultimately, the decision between a single-drum or double-drum atmospheric sterilizer depends on your specific needs and scale of operation. Both designs have their advantages, and it is important to consider factors such as space, efficiency, and automation when making your choice.
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Insulation: neoprene sheeting, radiator reflection foil, or rockwool
When it comes to insulating your mushroom sterilizer, you have a broad choice of materials. Neoprene sheeting, radiator reflection foil, and rockwool are all valid options. You can also consider Kingspan insulation. These materials can be attached in a variety of ways, but the most common method is to simply wrap your barrel with the chosen material and tape it with aluminium tape.
Neoprene sheeting is a good option if you have some lying around, as one person did when building their mushroom sterilizer. They cut the sheeting to the right circumference and height, knocked out three holes for the inlet, outlet, and element, and secured the sheeting to the barrel with contact adhesive along one strip.
Rockwool is another option, which can be wrapped around the barrel and taped with aluminium tape. Radiator reflection foil can be applied in the same way.
Kingspan insulation is another type of insulation that can be used to wrap the barrel and improve its thermal efficiency.
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Temperature control: PID controllers and thermostats
Temperature control is a critical aspect of building a mushroom sterilizer. While pasteurization involves lower temperatures, sterilization requires higher temperatures to effectively kill bacteria and other contaminants. To achieve and maintain the desired temperature, you can utilize PID controllers and thermostats.
PID controllers (Proportional-Integral-Derivative) are feedback controllers that use a control loop mechanism. They take the current temperature as input, compare it to the desired setpoint, and calculate the necessary adjustments to the heating element to reach and maintain the target temperature. PID controllers can be purchased or built, with options like the Inkbird Brewing Temp controller. When selecting a PID controller, ensure that it can handle the wattage or amps of your heating element to avoid overloading it.
Thermostats are another essential component for temperature control in mushroom sterilizers. They help maintain the ideal pasteurization temperature, which is typically around 70°C (158°F). The thermostat should be fitted to the inside bottom of the container. Additionally, consider including a thermal fuse in your design as a safety measure. Set the thermal fuse to a temperature above your normal operating range, such as 150°C, to protect the heating element in case of a dry run.
Temperature monitoring is crucial to ensure the effectiveness of the sterilization process. You can use devices like thermocouples to monitor temperatures inside the bags or containers. This provides valuable data to adjust your PID controller settings or thermostat settings accordingly.
It is important to note that the sterilization temperature requirements may vary depending on the specific mushroom species and substrate being used. For example, according to Stamets GGMM, heating the substrate to 91°C for 8 to 12 hours is recommended for enriched sawdust used in cultivating Shiitake mushrooms. However, keep in mind that at sea level, water boils at 100°C, and higher temperatures may be necessary to kill certain bacteria and endospores.
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Steam escape: drilling an exhaust port
Drilling an exhaust port in the lid of your mushroom sterilizer is a simple yet effective way to allow steam to escape in a controlled manner. This method is ideal for outdoor use, but if you plan to use your sterilizer indoors, you may want to consider additional measures to regulate the steam flow.
To create the exhaust port, you will need to drill a hole in the lid of your sterilizer barrel. Before drilling, it is important to determine the appropriate size and location for the hole. The hole should be positioned to avoid any potential blockage by bags or other components inside the barrel. A small spacer at the top of the barrel can help prevent blockage by ensuring there is a safe margin around the exhaust port.
When drilling the hole, it is crucial to use the correct tools and techniques to ensure a precise and clean cut. Using a Q-max cutter, drill a hole the diameter of the cutter's bolt from the outside of the lid. Unscrew the cutting portion and pass the bolt through the hole, then reattach the cutting portion on the inside of the barrel. Tighten the bolt and draw the cutter through until it falls out, leaving you with a smooth and accurate hole.
After drilling the hole, you can enhance the exhaust port by installing a valve to control the steam outflow. This addition provides the option of attaching an exhaust hose to direct the steam away from your workspace. It is important to consider the size of the hole and select an appropriate valve accordingly. You may also need to use screws and nuts to secure the valve in place and prevent mismatch drilling or drift.
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Pasteurisation: maintaining 70°C (158° F)
To build a mushroom sterilizer, you will need a large barrel, such as a 44-gallon drum, or a large plastic container with a tight-fitting, vented lid. The pasteurisation process requires maintaining a temperature of around 70°C (158° F). This is a much lower temperature than sterilisation and is, therefore, simpler and easier to achieve. However, it may require a longer run time and more energy to maintain this temperature over a sustained period.
To achieve pasteurisation, you will need a thermostat to control the temperature. You can use gas or fire as a heat source, but this must be done with care to avoid overheating. An electric heating element and thermostat can be fitted to the inside bottom of the container. You will also need a way to control the steam produced during the process. If you are using your steriliser outdoors, you can simply drill an exhaust port in the lid. For indoor use, you may want to control the flow of steam.
To make the barrel more thermally efficient, you can use insulating materials such as neoprene sheeting, radiator reflection foil, Kingspan insulation, or rockwool. These materials can be wrapped around the barrel and secured with aluminium tape. It is important to note that pasteurisation does not aim to kill all organisms within the substrate but rather allows certain beneficial ones to remain. This process is often used for growing mushrooms that decompose wood, and it is not typically used for field mushrooms, which are usually cultivated through composting.
Additionally, the cool-down period after pasteurisation is crucial. It should be done in very clean conditions to prevent contamination. Before pasteurisation, some materials, such as straw, should be shredded to increase the surface area exposed to the heat. Bulky materials like straw or wood chips can be pasteurised, but they will only be partially affected by the process due to their size and density.
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Frequently asked questions
The basic requirements include a drum, a heating element, and insulation. The drum can be made of stainless steel or ceramic-coated material, and it should have a tight-fitting lid with a steam escape mechanism, such as an exhaust port. The heating element is placed inside the drum, and the drum is insulated with materials like neoprene sheeting or rockwool.
For atmospheric sterilization, the substrate should be heated to 91°C for 8 to 12 hours. This is effective for enriched sawdust substrates used for growing Shiitake mushrooms and other similar varieties. The ideal pasteurization temperature is around 70°C, which requires a thermostat for control.
It is important to ensure that the sterilizer does not become pressurized, as this can be unsafe. A small spacer at the top of the barrel can help prevent this by providing a safe margin. Additionally, always drain the barrel after each use to prevent limescale and rust build-up, especially for mild steel and galvanized barrels.
To optimize performance, you can use a PID controller or a temperature controller to maintain the desired temperature. It is important to ensure that the wattage/amps of your element do not overpower the controller. Additionally, consider using a thermal fuse and a water overflow circuit for added safety. Regularly cleaning and sterilizing the equipment, including gloves and surfaces, will help prevent contamination.
