Sarah Brown
Mushroom cultivation is a delicate process that requires a sterile environment and strict adherence to precise guidelines to prevent contamination. The most common sources of contamination are air, water, substrate, equipment, and human handling, with bacteria, fungi, viruses, and parasites being the most common unwanted intruders. To prevent contamination, growers should ensure proper hygiene, use sterilized equipment and substrates, implement sanitation protocols, and control the growing environment by regulating airflow, humidity, and temperature. Additionally, using mold-resistant mushroom strains and regular monitoring can help manage mold issues.
| Characteristics | Values |
|---|---|
| Environment | Sterile, well-ventilated, regulated air flow, humidity, and temperature |
| Equipment | Sterilized, mold-resistant strains |
| Human Handling | Proper hygiene, use of personal protective equipment, gloves, masks, hairnets |
| Water | Sterilized, free from contaminants, reverse osmosis systems, UV light sterilization |
| Substrate | High-quality, sterilized, treated with fungicides and other chemicals |
| Other | Avoid over-watering, store in a cool, well-ventilated area, use laminar flow hoods, still air box, or SAB |
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What You'll Learn
Sterilise equipment and choose mould-resistant strains
Mushroom growers need to be aware of contamination from trichoderma, bacteria, mould and more. The most common causes of contamination are airborne contaminants and contamination from incorrectly sterilised or improperly pasteurised tools, substrates, and/or cultivators. To prevent contamination, it is important to establish a highly controlled and repeatable approach to substrate preparation.
Sterilise equipment
To completely eradicate contaminants from a substrate, cultivators must first prepare the substrate using one of two preparation methods: pasteurisation or sterilisation. Both methods are common for preparing mushroom substrates for spore inoculation. Pasteurisation involves exposing a substrate to mild dry or steam heat — usually less than 100°C (212°F) — for a brief period of time to kill off pathogens. This method is popular with smaller growing facilities because it does not require any special equipment — just a reliable heat source. Sterilisation, on the other hand, involves heating a substrate to temperatures above 120°C under pressure to kill any living or dormant contaminants. This method is more suitable for highly nutritious substrates.
To sterilise equipment, you can use a mushroom autoclave, which is designed for the sole purpose of using steam to sterilise substrates and other mycology equipment. This method allows for more control over the preparation process and has a far greater capacity than any pressure cooker. Another option is to use a stovetop pressure canner that is big enough to hold the material and can reach 15 PSI.
Choose mould-resistant strains
When choosing a mushroom strain to grow, consider selecting a mould-resistant strain, especially if you live in a humid environment or in a part of the world that gets very humid. Some mould-resistant strains that can be grown indoors include Purple Ghost Candy, Moby Dick, Sweet Tooth and Glookies. Mould-resistant strains that can be grown outdoors include Blue Venom, Holland's Hope and Frisian Dew.
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Maintain a sterile environment with good ventilation
Maintaining a sterile environment is crucial to preventing mushroom contamination. The cultivation area should be well-ventilated and free from potential contaminants. Here are some detailed steps to achieve this:
Firstly, identify all possible sources of contamination. Contamination can arise from various sources, including air, water, substrate, equipment, and human handling. Mould spores, bacteria, fungi, viruses, and parasites can enter the growing environment through these sources and wreak havoc on mushroom growth. Therefore, it is essential to implement prevention methods and maintain strict hygiene practices.
To minimise airborne contaminants, consider using a laminar flow hood or a still air box (SAB). These provide a clean stream of air, effectively reducing the risk of contamination. Additionally, ensure the cultivation area has good air circulation and ventilation. Regulating airflow is crucial in preventing the spread of mould and other contaminants.
Use only sterilised water that is free from pollutants. Water can introduce bacteria, fungi, and other harmful microorganisms into the growing environment. Reverse osmosis systems and UV light sterilisation can help ensure the water's purity.
The substrate used in mushroom cultivation should also be of high quality and free from contaminants. Sterilise the substrate before use by subjecting it to high pressure and temperature for an extended period. This process will eliminate any competing organisms and dormant spores that may hinder mushroom growth.
Lastly, practice good personal hygiene and use personal protective equipment (PPE) when handling mushroom cultures. Wash your hands thoroughly before handling any equipment or substrates. Gloves, masks, and hairnets can help prevent contaminants from being transferred from your body to the growing environment.
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Use clean hands and tools to avoid contamination
Human handling can introduce contaminants to the growing environment. Therefore, it is important to use clean hands and tools to avoid contamination when cultivating mushrooms. Before handling any equipment or substrates, make sure to wash your hands thoroughly with soap and water. It is also recommended to wear gloves to provide an additional layer of protection and prevent the transfer of any potential contaminants from your hands to the surface of the substrate.
Similarly, all tools and equipment should be thoroughly sterilized before each use. This includes knives, scissors, and any other cutting or cultivation tools. You can clean your tools with hot soapy water, and it is ideal to wipe them down with rubbing alcohol (isopropyl alcohol) to ensure they are free from any contaminants. Using clean tools is crucial because contamination can arise from various sources, including the equipment itself.
In addition to hand and tool hygiene, it is important to be mindful of your clothing and breathing. Your breath, clothes, and even the mushroom cultures or substrates themselves can harbour contamination. Therefore, it is recommended to wear protective clothing, such as a mask, hairnet, and a clean lab coat or apron, to minimize the risk of transferring contaminants from your body or clothing to the growing environment.
Furthermore, it is essential to work in a clean and controlled environment. This includes ensuring proper ventilation in the cultivation area and regulating airflow, humidity, and temperature to prevent the growth of unwanted organisms. Using laminar flow hoods or clean rooms can also help prevent contamination by creating a clean stream of air for mycological work and eliminating airborne contaminants.
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Avoid over-saturation and regulate humidity
Mushrooms require a humid environment to grow, with temperatures ranging from 55 to 60°F. However, it is crucial to avoid over-saturation to prevent mould growth. Over-watering can cause the mycelium to become patchy and even drown it. Therefore, it is important to maintain the right moisture balance and ensure proper air circulation.
To avoid over-saturation, it is recommended to keep the substrate at or below field capacity (68% hydration). This will help prevent mould growth and maintain optimal moisture levels for mushroom growth. It is also important to monitor the humidity levels regularly and make adjustments as needed to ensure consistent growth.
Proper air circulation is crucial in preventing mould growth. Cobweb mould, for example, thrives in high humidity and can spread rapidly. By increasing air circulation and lowering humidity, you can limit the potential for contamination by this type of mould. Additionally, certain moulds, such as orange bread mould, prefer warm and humid conditions. If the temperature rises above 25°C and the humidity is high, it is more likely that mould will become an issue.
To regulate humidity and improve air circulation, you can use tools such as hygrometers and thermostats. These tools will help you maintain the optimal environmental conditions for mushroom growth while reducing the risk of mould contamination. It is also important to inspect your mushrooms and substrate frequently for any signs of contamination, as early detection can make management easier.
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Use high-quality, sterilised substrates
When cultivating mushrooms, it is important to use high-quality, sterilised substrates to prevent contamination. Mushrooms are cultivated in a variety of substrates, including supplemented sawdust fruiting blocks, mushroom grain spawn, and coffee grounds. The substrate provides the mushroom mycelium with the nutrients it needs to develop and produce mushrooms.
The choice of substrate depends on the type of mushrooms being grown and their nutritional requirements. More nutritious substrates, such as those with high levels of supplementation like manure, soy hulls, grains, and master's mix, require sterilisation to eliminate all potential contaminants. Sterilisation involves heating the substrate to temperatures above 120°C under pressure to kill any living or dormant contaminants, including fungal spores. This process gives the mushroom mycelium a head start by eliminating competition from other organisms that also thrive in moist, nutrient-rich environments.
To sterilise a substrate, growers often use pressure cookers or autoclaves to achieve the required temperatures and pressure. For those without access to such equipment, barrel steam sterilisers are a popular alternative, as they can be built and operated at a lower cost. It is important to note that the substrate must be cooled to at least 30°C before inoculating it with spawn to avoid killing the mushroom spawn with residual heat.
While sterilisation is effective in eliminating all contaminants, it is not always necessary. Less nutritious substrates, such as straw, sugarcane bagasse, coco coir, hardwood sawdust, and cardboard, can be pasteurised instead. Pasteurisation involves heating the substrate to temperatures between 65°C and 85°C for 1.5 to 2 hours, reducing the population of competing organisms without eliminating them completely. Coffee grounds, for example, do not require pasteurisation or sterilisation if they are used quickly and handled with proper hygiene.
By using high-quality, sterilised substrates, mushroom growers can minimise the risk of contamination and provide their mushrooms with the best possible environment to thrive.
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Frequently asked questions
The air is a very likely source of contamination for mushroom growers. Mold spores and other contaminants are everywhere, though invisible to the naked eye. To reduce contaminants in the air, use a laminar flow hood, a still air box (SAB), or a HEPA filter.
Use sterilized water that is free from contaminants to prevent waterborne contamination. Use reverse osmosis systems and UV light sterilization to ensure the purity of the water.
Maintain proper hygiene and use personal protective equipment such as gloves, masks, and hairnets when handling mushroom cultures. Wash your hands before handling equipment and avoid touching the substrate and plastic.
