John Miller
Mushroom culture is the process of cultivating mushrooms, which can be done indoors or outdoors. The process involves several stages, including strain selection, substrate preparation, inoculation, incubation, initiation, fruiting, and harvest. The substrate, or growth medium, can be logs, straw, wood, or compost, and it must be prepared by ensuring optimal moisture content and cleanliness. Inoculation involves introducing the mushroom culture to the substrate, which can be done through spores or tissue culture. Tissue culture allows cultivators to preserve the genetic character of the contributing mushroom. After inoculation, the substrate is incubated, and once it is ready, initiation occurs, followed by fruiting and harvest.
| Characteristics | Values |
|---|---|
| Definition | A mushroom culture is a sterile laboratory environment where a cultivator removes a select species from the outdoors to create an optimized environment for the mushroom mycelium to grow. |
| Mushroom growth | Mushrooms derive all their energy and growth materials from their growth medium, through biochemical decomposition processes. |
| Light | Some fungi use light as a signal for fruiting. |
| Humidity | Mushrooms grow well at relative humidity levels of 95–100% and substrate moisture levels of 50 to 75%. |
| Spores | Mushrooms reproduce through spores, which can be contaminated with airborne microorganisms, interfering with mushroom growth. |
| Mycelium | Actively growing mushroom culture is placed on a substrate, usually sterilized grains such as rye or millet, and induced to grow into those grains. |
| Inoculation | Inoculated grains (or plugs) are referred to as spawn. Spores are another inoculation option but are less developed and easily contaminated. |
| Growing techniques | All mushroom growing techniques require the correct combination of humidity, temperature, substrate (growth medium), and inoculum (spawn or starter culture). |
| Commercial technique | Indoor tray growing is the most common commercial technique, followed by containerized growing. |
| Stages of cultivation | Strain selection, substrate preparation, inoculation, incubation, initiation, fruiting, and harvest. |
| Sterilization | Complete sterilization is not required or performed during composting. Instead, a pasteurization step is included to allow some beneficial microorganisms to remain in the growth substrate. |
| Pinning | The trickiest part of mushroom growing, as a combination of carbon dioxide concentration, temperature, light, and humidity triggers mushrooms towards fruiting. |
| Tissue culture | Once mastered, this is the simplest way to grow mushrooms and is a proven way to "screen" strains for their cultivation potential. |
| Micron filters | Solves the problem of contamination in the laboratory and is highly cost-effective. |
| Spawn | G1 Masters are best grown in regular-mouth quart mason jars, while G2 spawn is best grown in half-gallon or gallon jars. |
| Liquid culture | Liquid culture is a revolutionary improvement over traditional methods, allowing cultivators to inoculate hundreds of grain jars from a single petri dish. |
| Health benefits | Some cultures have used mushrooms as medicine and dietary staples for the past two thousand years. |
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What You'll Learn
Growing from spores vs. tissue
Mushrooms are the fleshy, spore-bearing fruiting bodies of a fungus, typically produced above ground on soil or another food source. They grow well at relative humidity levels of around 95-100% and substrate moisture levels of 50 to 75%. Instead of seeds, mushrooms reproduce through spores, which are their "seeds". Spores can be contaminated with airborne microorganisms, which will interfere with mushroom growth and prevent a healthy crop.
Mushroom cultivators can grow mushrooms from spores or tissue. Growing from spores is fairly involved and requires some equipment to be successful. Spores are almost always contaminated, so cultivators must put them on agar and keep doing transfers until they have a clean culture. From there, cultivators can use the mycelium on the agar to inoculate spawn directly or make some liquid culture.
To collect spores, one must find a mushroom and place it on a piece of paper, exposing the gills located on the underside of the mushroom's head. Then, the mushroom is laid down onto the paper, gill-side down, and covered with a glass for 24 hours. After this period, the spores will have left a print on the paper, which can be rehydrated with sterile water and used to inoculate a chosen medium.
However, since spores are easily contaminated, they are only manipulated in laboratory conditions with a laminar flow cabinet. In contrast, growing from tissue is much easier and allows cultivators to preserve the exact genetic character of the contributing mushroom. Tissue culture is a highly individualized art, but it is the simplest way to grow mushrooms once mastered.
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Outdoor vs. indoor cultivation
Mushroom cultivation, or fungiculture, involves creating the right conditions for mushrooms to grow from spores. Mushrooms can be grown both outdoors and indoors, and each method has its advantages and disadvantages.
Outdoor Cultivation
Outdoor mushroom cultivation has been practised for centuries, with mushrooms being grown on logs in the woods. Mushrooms can be grown outdoors in shady environments with good humidity and airflow, creating ideal fruiting conditions without the need for climate control. Outdoor systems use less energy than indoor systems and can support sustainable forest management practices. Additionally, outdoor cultivation can be more economical due to lower infrastructure and start-up costs.
However, outdoor mushroom production has its limitations. It may be challenging to access logs or a suitable growing environment in urban and peri-urban areas. Outdoor production is also subject to the unpredictability of the climate, making production cycles less predictable.
Indoor Cultivation
Indoor mushroom cultivation provides a controlled environment with stable temperature and humidity levels, allowing for year-round growth. This method offers a buffer against the unpredictable aspects of weather and climate, ensuring reliable and precise environmental conditions. Indoor production can be adapted to various spaces, including abandoned farm infrastructure, basements, shipping containers, and warehouses, making it accessible to both rural and urban farmers.
The main benefit of indoor cultivation is faster mushroom growth. However, space limitations can be a challenge, especially in small living quarters or shared spaces. Creating the necessary dark and humid conditions may be difficult in certain indoor settings, and the aroma produced during mushroom growth may be unpleasant or undesirable for some individuals.
Hybrid Systems
Some farmers employ a hybrid approach, combining outdoor and indoor cultivation methods. For example, shiitake logs may be brought indoors to extend the growing season, while blocks may be taken outdoors to fruit during favourable natural conditions.
Both outdoor and indoor mushroom cultivation techniques have their advantages and considerations. Outdoor cultivation provides natural growing conditions and supports sustainable practices but may be limited by species availability and climate unpredictability. Indoor cultivation offers a controlled environment, faster growth, and adaptability to various spaces but may be constrained by space limitations and the need for specific conditions. Ultimately, the choice between outdoor, indoor, or hybrid cultivation depends on the grower's specific circumstances, resources, and goals.
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Substrate preparation
Selecting the Right Substrate
The first step is to choose a suitable substrate that meets the preferences and requirements of the mushroom species you plan to cultivate. Different mushrooms thrive on different substrates, so it's important to do your research. Some common substrates include straw, sawdust, cardboard, coffee grounds, wood chips, and agricultural wastes like corn stalks.
Substrate Availability and Ease of Preparation
Consider the availability and ease of working with a particular substrate. For example, straw-based substrates are easily accessible and can be prepared using basic home utensils. Select a substrate that is readily available in your area to simplify the preparation process.
Mixing and Moistening the Substrate
Depending on the substrate, you may need to mix it with other materials to provide additional nutrients and improve structure. For example, when using straw, you can add 20% straw to the mix for better air exchange. You may also need to moisten the substrate mixture to achieve the desired dampness, ensuring it's not dripping water when squeezed.
Pasteurization or Sterilization
Before inoculating the substrate with mushroom spores or mycelium, it is crucial to pasteurize or sterilize it. This process kills any competing mould, bacteria, or other microorganisms that may hinder the growth of your desired mushroom species. Pasteurization involves heating the substrate in hot water or steam at temperatures between 70-80°C for at least one to two hours. This method eliminates most contaminants while preserving beneficial microorganisms. Sterilization, on the other hand, is a more intense process, requiring temperatures above 120°C or 250°F, along with pressure, to completely eliminate all microbial life, including beneficial bacteria. The choice between pasteurization and sterilization depends on the nutrient content of the substrate and the specific mushroom species.
Containerization
After pasteurization or sterilization, place the substrate into its final container. Commercial growers often use large clear plastic bags, while home growers may use smaller containers like mason jars or buckets.
Inoculation
Once the substrate is in its container, it's time to inoculate it with mushroom spawn or spores. This is the point where the mushroom growth process truly begins, as the spores or mycelium will now have a contaminant-free and nutrient-rich environment in which to develop and bear fruit.
Remember, proper hygiene during substrate preparation is vital to avoid contamination. Additionally, some experimentation may be necessary to find the perfect substrate recipe for your specific mushroom species and growing conditions.
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Inoculation
There are different methods of inoculation, including grain inoculation, liquid inoculation, and seed inoculation. Grain inoculation involves using grain spawn to inoculate straw, sawdust, and other substrate mixes. Liquid inoculation uses mycelium growing in a nutrient-rich solution or mushroom spores in a sterile solution to inoculate a substrate. Seed inoculation can be done in a jar or a bag. Liquid inoculation is one of the easiest methods as it only involves spraying a substrate with a liquid culture. It also has a lower risk of contamination compared to other methods.
To inoculate a substrate, you need to have a syringe of liquid culture of the mushroom variety of your choice. Before using the liquid culture syringe, gently shake it for one minute to evenly distribute the mycelium throughout the liquid. This will ensure a more consistent inoculation. Creating a sterile work area is crucial to prevent contamination during the inoculation process. After inoculation, the mycelium will propagate during the incubation phase, following which it is possible to move on to the fruiting phase to pick the mushrooms.
The inoculation rate also impacts the speed of colonization. Two methods of distribution commonly used are "top spawning" and "through spawning". Top spawning is the process of adding spawn on top of the substrate and letting it grow down. Through spawning involves adding alternating layers of spawn and substrate.
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Harvesting
The harvesting stage of mushroom culture is the culmination of the previous steps of strain selection, substrate preparation, inoculation, incubation, initiation, and fruiting. Harvesting techniques vary depending on the species of mushroom, the growing medium, and the environment. Here is a detailed guide to the harvesting process:
Timing
Mushrooms can be harvested 18 to 21 days after casing. However, the harvest time can vary depending on the size and type of wood, species of fungi, and environmental factors such as temperature, humidity, and rainfall. For example, shiitake mushrooms require 12 to 15 months of incubation, followed by soaking in water for 24 hours, and then seven to ten days before they are ready for harvest.
Ventilation and Watering
Ventilation and watering play a crucial role in the quality and yield of the mushroom crop. It is generally recommended to ventilate as little as possible until the mycelium appears on the surface of the casing. Introducing fresh air too early can cause the mushrooms to grow below the surface, resulting in dirty mushrooms at harvest time. Similarly, watering should be stopped when pin initials are forming to prevent mushrooms from forming below the surface.
The terms "flush", "break", or "bloom" refer to the 3- to 5-day harvest periods during the cropping cycle. These periods are followed by a few days when no mushrooms are available to harvest. This cycle repeats itself, allowing for continuous harvesting as long as mushrooms continue to mature.
Outdoor Log Harvesting
Outdoor log inoculation is a traditional method that has been used for hundreds of years. Tree logs are inoculated with spawn and allowed to grow in wild conditions. Seasonal changes or briefly soaking the logs in cool water trigger fruiting. This method is unpredictable and highly dependent on the seasons, so less than 5% of commercially sold mushrooms are produced this way.
Indoor Tray Harvesting
Indoor tray growing is the most common commercial technique. It offers scalability and easier harvesting compared to other methods. Sterilization is not typically performed during the composting stage, but pasteurization is often included to retain beneficial microorganisms. Pinning, or triggering fruiting, is the most challenging part of indoor tray growing as it requires precise control of carbon dioxide concentration, temperature, light, and humidity.
All-in-One-Bag Harvesting
The All-in-One-Bag method is a user-friendly and contamination-resistant approach. When harvesting, the preferred method is to cut out the entire "cake" (the colonized block) and place it in a clear tub. Fanning the tub for 30 seconds daily and maintaining moisture on the sides are essential for successful harvesting.
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Frequently asked questions
A mushroom culture is a way to grow mushrooms by cultivating their mycelium in a controlled environment, usually indoors, to protect them from the competition of the outdoors.
Mycelium is the actively growing part of a mushroom, which can be placed on a substrate—usually sterilised grains—and induced to grow into those grains.
A substrate is any material that is a food source for mushroom mycelium. Common substrates include logs, stumps, woodchips, straw, sawdust, coffee grounds, grain hulls, and other carbon-rich materials.
Inoculation is the process of drilling holes in a substrate, filling the holes with cultured mycelium or inoculum, and then sealing the holes. The inoculated grains or plugs are referred to as spawn.
Spawn is the grain or sawdust/bran that has been inoculated with mushroom mycelium. Spawn can be used to inoculate other substrates such as straw, wood, or compost.
