Sarah Brown
Mushroom inoculation is the process of inserting mushroom spores or spawn into a suitable growth medium, such as logs, stumps, straw, or sawdust. The spawn then feeds on and colonizes the substrate, leading to mushroom growth. There are various inoculation methods, including liquid inoculation, dry inoculation, and plug spawn inoculation. The choice of method depends on the type of mushroom, substrate, and growing conditions. For instance, outdoor inoculation methods have less concern for introducing contaminants, whereas indoor methods require a sterile environment. The inoculation rate, or the amount of spawn added, is also crucial, as it affects the speed of spawn run and colonization time.
| Characteristics | Values |
|---|---|
| Process | Inserting mushroom spawn into a substrate suitable for growth |
| Substrates | Logs, stumps, woodchips, straw, sawdust, coco coir, coffee grounds, etc. |
| Timing | Logs should be inoculated between one day and three weeks after the tree is felled; winter and spring inoculations are ideal |
| Contamination prevention | Sterilize the space, surfaces, and tools; use gloves; wipe surfaces with alcohol |
| Inoculation methods | Dowel, sawdust, layering, liquid, dry, plug spawn, top spawning, through spawning |
| Spawn distribution methods | Top spawning, through spawning |
| Spawn distribution factors | Nutrient level of the substrate, speed of spawn run, economics |
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What You'll Learn
- The culture stage: Grow mycelium in a petri dish or liquid culture
- The grain spawn stage: Use the culture to inoculate sterilized grain
- The sawdust spawn stage: Inoculate sawdust to create spawn for growing mushrooms outdoors
- The bulk substrate stage: Use grain or sawdust spawn to inoculate bulk substrates
- Timing: Logs can be inoculated immediately after they are felled
The culture stage: Grow mycelium in a petri dish or liquid culture
The culture stage is a pivotal step in the mushroom cultivation process, serving as the foundational layer for the entire growth journey. It involves growing mycelium in a petri dish or liquid culture. Here's how to do it:
Using a Petri Dish
Petri dishes are flat, transparent containers, usually made of plastic or glass, that provide a controlled environment for growing and observing microorganisms. To use a petri dish for mushroom culture:
- Prepare a sterile environment by wiping surfaces with isopropyl alcohol and using a laminar flow hood or still air box.
- Find a healthy mushroom fruiting body and, in a sterile environment, clean its surface with a cotton swab soaked in isopropyl alcohol.
- Using a sterilized scalpel, cut a small piece of the internal tissue from the mushroom.
- Place the tissue in a Petri dish containing a growth medium, such as Sabouraud agar enriched with chloramphenicol to limit bacterial growth.
- Once the mycelium has developed on the initial agar, transfer a piece of healthy mycelium to a new Petri dish containing a more nutritious growth medium, such as MEA agar.
- Continue transferring the mycelium to fresh agar plates to ensure its health and purity.
Using Liquid Culture
Liquid culture is a nutrient-rich solution used to propagate mycelium. It provides a temporary environment for the mycelium to grow and multiply. To create a liquid culture:
- Combine water with nutrients like malt extract or dextrose in a jar with gas exchange and injection port capabilities.
- Sterilize the mixture by pressure cooking it at 15 PSI for 30 minutes.
- Allow the mixture to cool naturally to room temperature before inoculation.
- Set up a sterile workspace by wiping down surfaces and using sterile equipment.
- Use a sterile syringe to transfer a spore solution or mycelium from an existing culture into the nutrient solution.
- Seal the jar and stir to distribute the mycelium or spores evenly throughout the liquid.
- Place the jar in a warm, dark area at around 75-80°F (24-27°C) and monitor daily for signs of mycelial growth, which will appear as cloudy, white patches.
- Once significant growth is observed, shake the jar to break up the mycelium and promote further growth.
- Test for contamination by checking for strange colours or odours before using the liquid culture to inoculate your substrate.
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The grain spawn stage: Use the culture to inoculate sterilized grain
The Grain Spawn Stage: Using the Culture to Inoculate Sterilized Grain
The grain spawn method is a popular technique for cultivating mushrooms, offering several advantages over other methods. It provides an ideal substrate for mushroom growth, allowing for rapid colonisation and the development of a robust mycelium network. Additionally, grain spawn can be easily scaled up or down, making it versatile for both commercial and hobbyist cultivators.
To begin the grain spawn stage, you'll need to prepare sterilised grain. Commonly used grains include rye, wheat, millet, or a combination of these. Sterilisation is crucial to eliminate any contaminants that may compete with the mycelium for resources or introduce unwanted microorganisms. This can be achieved through pressure cooking or steam sterilisation. Ensure your grain is moist but not soggy – it should have the consistency of a wrung-out sponge.
Once your grain is sterilised and cooled, it's time to introduce the mushroom culture. This process is known as inoculation. Working in a sterile environment is essential to avoid contaminating your grain spawn. Set up your workspace with clean surfaces, sterilise your tools with alcohol or a flame, and consider using a laminar flow hood if possible.
Open your prepared grain bags or jars and carefully introduce the mushroom culture. Typically, this involves transferring a small piece of mycelium, known as a "culture slant," from its sterile container onto the grain. Use a sterile tool, such as a scalpel or forceps, for this process. Gently mix the culture into the grain, ensuring even distribution.
Seal the grain spawn containers tightly after inoculation. Store them in a warm, humid environment, ideally at a temperature of around 25°C (77°F). Maintain a relative humidity of 60-70% to encourage optimal colonisation. Regularly check your grain spawn for signs of contamination, such as mould or discolouration, and inspect for mycelium growth.
Depending on the mushroom species and environmental conditions, colonisation of the grain spawn can take several weeks to a month. You'll know it's ready when the grain is mostly covered in healthy, white mycelium. At this point, you can move on to the next stage of mushroom cultivation, whether it's creating bulk substrate or directly introducing the grain spawn to a growing medium.
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The sawdust spawn stage: Inoculate sawdust to create spawn for growing mushrooms outdoors
The sawdust spawn stage involves using grain spawn to inoculate sawdust to create spawn for growing mushrooms outdoors. This method is commonly used for growing mushrooms on a commercial scale. It is also used for outdoor mushroom beds and logs.
To begin, you will need to gather your supplies and equipment. Hardwood sawdust is a common substrate for mushroom cultivation as it is readily available and relatively cheap. Oak, beech, or maple are ideal choices, but ensure the sawdust is from untreated wood to avoid harmful chemicals.
Once you have your substrate, you will need to drill holes into it. Then, fill the holes with the grain spawn. This can be done using a special tool (inoculator) that can be purchased or homemade. The inoculator is used to insert the sawdust into the hole. After the holes are filled, cover the surface of each hole with wax to ensure optimal mycelium growth and reduce contamination by other fungi species.
Once the substrate is fully colonized, it can be used to grow mushrooms. This process typically takes 2-4 weeks, depending on the mushroom species and environmental conditions. It is important to monitor the substrate during this time to ensure that it is in a dark, clean space with a stable temperature suitable for your mushroom species.
Sawdust spawn is a great choice for those looking to grow gourmet mushrooms as it is relatively easy to work with and produces good results. It is also a versatile method that allows for customisation with supplements to enhance nutrition and mushroom growth.
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The bulk substrate stage: Use grain or sawdust spawn to inoculate bulk substrates
The Bulk Substrate Stage
The bulk substrate stage is the final stage of the mushroom inoculation process. It involves using grain or sawdust spawn to inoculate bulk substrates like straw, supplemented sawdust, or logs to grow mushrooms. Before inoculating a substrate, you need to gather the necessary supplies and equipment, including buying or making mushroom culture or spawn.
The type of substrate used depends on the mushroom species being grown. Substrates with low nutritional values, such as cardboard, straw, sugarcane bagasse, coco coir, and unsupplemented hardwood sawdust, do not require sterile conditions for inoculation. These substrates can be inoculated in a clean room with minimal airflow, but it is important to ensure that hands are washed and work surfaces and tools are wiped down before beginning.
When growing mushrooms outdoors using low-nutrient, carbon-rich substrates, such as logs or garden beds with wood chips or straw, inoculation can be done in normal outdoor conditions. However, if you plan to create grain spawn or grow mushrooms on nutrient-rich substrates, sterile conditions are necessary for inoculation.
Some cultivators choose to cover the uncolonized substrate with plastic wrap or tin foil after spawning to maintain moisture, block contaminants, and limit airflow. This step is optional, but it can help simulate the conditions of the underground stage of the fungus' life cycle. Pasteurized substrates are more resistant to contamination than sterilized substrates, and spawning can be done in the open air.
To inoculate a bulk substrate, you will need fully colonized grain spawn. This can be achieved by filling a plastic "oven bag" with the substrate and baking it in an oven at 160-180°F for 2-4 hours. Once the grain spawn is ready, follow these steps:
- Place your pasteurized substrate in a container where it can be mixed with the spawn. This could be the intended fruiting chamber, another large plastic tub, or even the bag in which the substrate was pasteurized.
- Shake the spawn jars to break up the colonized grain and ensure it is no longer in large clumps.
- Mix the spawn with the substrate as evenly as possible. Uneven distribution may result in longer colonization times and provide more opportunities for contaminants to grow.
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Timing: Logs can be inoculated immediately after they are felled
Inoculating logs with mushroom spores is a process that involves introducing mushroom spores or mycelium to suitable organic matter. This process is called inoculation. The sooner you inoculate the logs after felling the trees, the better. Research shows that the less time that elapses from felling until bolt inoculation, the greater the production per log. Logs can be inoculated immediately after they are felled, and there is no need to cure the log for a few weeks. However, you should not wait longer than three weeks to inoculate, as the log is more likely to be infested with competitive fungi or dry out.
To inoculate logs, you will need to drill a series of small holes into each log. The holes should be drilled starting two inches from the end of the log and spaced six to eight inches apart. Make the rows of holes three to four inches apart along the girth of each log. Use a 5/16-inch bit for plug spawn and drill the holes 1 1/4 inches deep.
Once the holes have been drilled, they need to be tightly packed with spawn. The type of spawn you use will depend on the mushroom variety you are growing and your preferences. Plug spawn is simple to use and only requires a drill and hammer or mallet. However, it is more expensive per log, and the mycelium may take longer to migrate into the sapwood of the log. Sawdust spawn, on the other hand, is slightly cheaper and allows the inoculator to work faster, but it requires a special tool (inoculator) to insert the sawdust into the hole. After packing the holes with spawn, cover the surface of each hole with wax to ensure optimal mycelium-growing conditions and reduce contamination by other fungi species.
After inoculation, the logs should be stacked criss-cross in full shade during the colonization period, preferably off the ground. Keep the logs outside in the elements and do not cover them, as they need access to water and rain. Keep them in a shaded area to avoid direct exposure of the spawn to sunlight and to minimize moisture loss. Logs should be watered if their internal moisture content drops below 35% prior to inoculation. Depending on the mushroom and wood species, it can take anywhere from four months to two years for the mushrooms to grow.
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Frequently asked questions
Mushroom inoculation is the process of inserting mushroom spores or spawn into a substrate that is suitable for growth.
A substrate is any material that is a food source for mushroom mycelium. Examples include logs, stumps, woodchips, straw, sawdust, coco coir, and coffee grounds.
Logs can be inoculated anytime between one day and three weeks after the tree is felled. Research shows that winter and spring inoculations are ideal, but summer and fall inoculations also produce sizable harvests.
There are three common types of spawn: plug spawn, sawdust spawn, and grain spawn. Plug spawn is simple to use and only requires a drill and hammer or mallet. Sawdust spawn is commonly used for larger substrates and outdoor growing. Grain spawn is typically used for indoor growing and is used to inoculate straw, sawdust, and other substrate mixes.
First, prepare the substrate by ensuring optimal moisture content and cleaning it of contaminants. Then, bring the spawn into contact with the substrate. Depending on the substrate, this may involve drilling holes into a log, cutting wedges into a stump, or mixing spawn into individual bags. Finally, place the inoculated substrate in the appropriate environment for growth.
