Sarah Brown
Mushroom cultivation, or fungiculture, is the process of growing mushrooms for food, medicine, construction materials, and other products. The process is unique to that of fruits and vegetables, as mushrooms are a type of fungus that requires different conditions for optimal growth. While sunlight provides an energy source for plants, mushrooms derive all of their energy and growth materials from their growth medium through biochemical decomposition processes. The growth medium, or substrate, is typically a mixture of grain, water, and chalk that has been treated with mycelium (thin, thread-like cells). This mixture is then pasteurized or sterilized before the mycelium is added, marking the beginning of the active mycelial growth phase. The mycelium spreads throughout the substrate, allowing the mushrooms to obtain the nutrients they need to grow. The growing environment must be carefully controlled in terms of temperature, humidity, and carbon dioxide levels to promote growth and trigger fruiting.
| Characteristics | Values |
|---|---|
| Time to grow | About 14 weeks |
| Growing environment | Highly controlled, indoor rooms with long growing beds stacked 4-10 rows high |
| Temperature | Carefully controlled |
| Humidity | Carefully controlled |
| Carbon dioxide levels | Carefully controlled, with a maximum of 0.08% during the growing period |
| Light | Required by some fungi as a signal for fruiting |
| Spawn | A substance treated with mycelium, typically made from a stored culture (millet, rye, wheat) |
| Substrate | Pasteurized or sterile |
| Mycelium | The root-like structure of fungi, which spreads throughout the substrate and allows mushrooms to get nutrients |
| Pinning | The trickiest part of growing mushrooms, where a combination of carbon dioxide concentration, temperature, light, and humidity triggers mushrooms towards fruiting |
| Yield | Mushrooms can produce four to five 'flushes' from one growing cycle, which can last up to 3 weeks with constant harvesting |
| Commercial methods | Log culture, bag culture, tray growing, artificial logs |
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What You'll Learn
The production process: composting, spawning, casing, pinning, cropping
The production process for cultivating mushrooms involves six key steps: Phase I composting, Phase II composting, spawning, casing, pinning, and cropping. The entire process, from the start of composting to the final steam-off after harvest, typically takes around 14 weeks to complete.
Phase I composting involves mixing organic materials such as wheat straw, dehydrated poultry manure, and horse manure. Water is added, and supplements like nitrogen and gypsum are mixed in periodically as the compost is aerated. This mixture undergoes aerobic fermentation, creating an ideal food source for mushrooms.
Phase II composting completes the process by pasteurizing the compost to remove ammonia. This step is crucial, as poor preparation can lead to issues with spawn growth and contamination by moulds and diseases.
Spawning is the introduction of mushroom mycelium (spawn) to the sterile compost. The spawn is typically made from stored cultures like millet, rye, or wheat and is used to seed the compost.
Casing involves adding a layer of casing soil or a mixture of peat moss and limestone to the spawn-run compost. This step provides a water reservoir and a medium for rhizomorphs (thick mushroom mycelia) to form.
Pinning is a critical step where mushroom initials or "pins" develop on the rhizomorphs. Lowering the carbon dioxide content of the air to 0.08% or lower by introducing fresh air triggers pinning. Pinning impacts both yield and crop quality.
Cropping is the final step where mushrooms are harvested over multiple flushes or breaks, typically within a 30-40 day period. Maintaining ideal temperature and humidity conditions is essential for successful cropping.
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The role of mycelium in mushroom growth
Mushroom cultivators harness the growth of mycelium, the root-like structure of fungi, to promote the growth of mushroom fruiting bodies. Mycelium is the primary "plant" portion of the mushroom and is the longest-living part of the organism. It is the first stage of the mushroom life cycle, which consists of three stages similar to the different stages found in plants.
Mycelium consists of thousands of intricate, interwoven, root-like filaments called hyphae. These filaments are only one cell wall thick, with highly active cells that serve many important functions, including acting as the immune response of the fungal organism. Mycelium is like the "mother plant" of a perennial, where the mother continues to live for many months, years, or even decades, while the flower or fruiting body blooms seasonally and then dies. The fruiting body is the above-the-surface, easily identifiable part of the mushroom organism.
Mycelium grows by absorbing nutrients from its environment. It secretes digestive enzymes onto its food source, often dead organic material, and sometimes living organisms, to break it down into smaller units that can be absorbed. Fungi can also form networks with plant roots, creating a cross-kingdom web known as mycorrhizal networks. Through photosynthesis, trees and other plants produce sugars and fats, which the fungi can get from the roots into their mycelium. In turn, the fungi help the trees and plants absorb water and nutrients from the soil beyond the reach of their roots and root hairs.
Mycelium is also crucial for fungal reproduction. The mycelia of two compatible fungi can fuse together, allowing the cells of each fungus to combine and their DNA to mix. After fusing, the cells end up in new spores held inside (like in truffles) or exposed outside (like in mushrooms) the fungus' reproductive structures. This is how some fungi reproduce sexually when the environmental conditions are right.
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Environmental conditions: temperature, humidity, carbon dioxide levels
Environmental conditions are crucial for successful mushroom production. The temperature, humidity, and carbon dioxide levels in the growing room must be carefully controlled to promote mushroom growth.
Temperature plays a vital role in mushroom cultivation. During the steaming process, temperatures should reach at least 150°F for a minimum of 12 hours to eliminate any pathogens. Mushrooms require cooler temperatures for optimal growth, especially during the fruiting stage.
Humidity is another critical factor. Mushrooms thrive in moist environments, and maintaining proper humidity levels is essential for their development. Spraying with a hose once a day during the initial stages of mushroom formation encourages the development of beautiful pin sets. After soaking, it is crucial to allow the blocks to dry out for 12-24 hours before covering them with plastic.
Carbon dioxide (CO2) concentration is a key factor in triggering the fruiting process. In the vegetative growth phase, CO2 levels increase as the mycelium is sealed in a gas-resistant barrier, trapping the gases produced by the growing mycelium. To induce pinning, the barrier is opened, causing a decrease in CO2 levels to the ambient atmospheric level of around 0.04-0.08% or lower, depending on the cultivar.
Additionally, light conditions play a role in mushroom production. While mushrooms do not rely on photosynthesis like plants, some fungi use light as a signal for fruiting. Therefore, light exposure should be considered when creating the optimal environment for mushroom cultivation.
Overall, by carefully controlling temperature, humidity, carbon dioxide levels, and light exposure, mushroom growers can create the ideal environment to promote the growth and fruiting of mushrooms.
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Common issues: contamination, pathogens, mould
Contamination, pathogens, and mould are common issues in mushroom cultivation. These issues can cause crop failure, so it is important to be aware of them and take preventative measures.
Contamination, or 'contam' in grower slang, refers to anything in the substrate or mycelium that negatively impacts mushroom growth. This includes bacteria, moulds, and animal pests. The human body is the greatest source of contamination, as human hands and clothes contain many bacteria and spores that can ruin crops. To reduce the risk of contamination, it is important to practice good sterile technique, which includes showering and using hand sanitiser before working with mushrooms, wearing clean clothes and a face mask or mouth covering, and not talking when working near open containers.
Mould is a type of fungus that grows in the form of filaments called hyphae. It can be controlled with salt, baking soda, alcohol, or cinnamon. Cobweb mould is a common type of mould that thrives in high humidity and stagnant air. To prevent and control cobweb mould, it is important to lower humidity and increase air circulation. Trichoderma is another type of mould that preys on other fungal mycelium and is distinguished by its vibrant blue-green colour during sporulation. It is one of the most difficult types of mould to contain. Green mould, caused by Trichoderma harzianum, is the most widespread disease in the US Agaricus industry and is characterised by an aggressive white mycelium that causes soft rot and produces emerald green spores.
Bacteria are unicellular microorganisms that reproduce very quickly and can be dealt with through pasteurisation and sterilisation of the substrate. One common type of bacterial contamination is Bacillus spp., also known as "wet spot" or "sour rot." This type of bacteria can survive the pressure cooking process, so mushroom cultivators must soak their grains for 12 to 24 hours before hydrating or sterilising them to kill off any heat-resistant endospores.
Pathogens can also survive post-crop pasteurisation if they grow into the wood. Therefore, it is important to steam the grow room after removing the substrate and washing down the beds. The temperature should be no less than 150°F for at least 12 hours.
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Commercial cultivation methods: log culture, bag culture, tray growing
Commercial mushroom cultivation methods can vary depending on factors such as scale, species, substrate, and resources. Here is an overview of three common commercial cultivation methods: log culture, bag culture, and tray growing.
Log Culture
Log culture is a traditional method that has been used in Asian cultures for centuries. It involves growing mushrooms on logs, pillars, or stumps. This method is hyper-organic, recycling forest waste and regenerating soil. Logs are inoculated with spawn, typically during the fall or winter, and can be shocked to create a flush of mushrooms. Shiitake mushrooms are a popular choice for log culture as they can be soaked or shocked weekly from May/June to October to produce 4-5 lbs over three seasons. Other species that can be grown on logs include oyster, lion's mane, and reishi mushrooms. Log culture is labour-intensive and has longer yield times, but it is a sustainable and low-cost method.
Bag Culture
Bag culture is a widely used and inexpensive method that offers flexibility in terms of species and substrate combinations. It is commonly used for specialty and exotic mushroom cultivation and is suitable for distributed farming as it does not require a single location. Bags are typically made of plastic and are designed to reduce contamination and increase yields. However, the use of single-use plastic bags is a notable downside, although the resource efficiency of mushroom farms may offset this impact. Growers can also opt for reusable bottles or ziplock bags, although these may be more time-consuming to clean between crops.
Tray Growing
Tray growing is a method commonly used for coprophilous (dung-loving) fungi, such as Agaricus (button, cremini, portobello) mushrooms, which are often found in soils enriched with dung and compost piles. This method is highly mechanized and accounts for a significant market share in the US. Trays are well-suited for growing mushrooms that prefer tray-like formations. While trays are commonly used, other containers such as buckets, bottles, jars, and tubs may also be utilized, depending on the specific requirements of the mushroom variety being cultivated.
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Frequently asked questions
The production process for mushrooms involves six main steps: Phase I and Phase II composting, spawning, casing, pinning, and cropping. The entire process takes about 14 weeks to complete.
There are several methods for mass-producing mushrooms, including:
- Tray culture: This method is highly mechanized and commonly used for coprophilous (dung-loving) fungi.
- Bag culture: This inexpensive method offers great flexibility in terms of species and substrate combinations, but it is labor-intensive and not easily mechanized.
- Log culture: This traditional method involves placing logs outdoors in stacks or piles and allowing them to grow in wild conditions.
- Indoor sawdust blocks: This is the largest-scale method for specialty mushroom production.
Mushrooms require specific conditions for optimal growth, including controlled temperature, humidity, and carbon dioxide levels. Adequate management of starting ingredients and proper environmental conditions are critical for successful mushroom production. Additionally, careful compost preparation can reduce potential problems during the spawn-growing period.
One of the biggest challenges in mushroom production is contamination, especially in the early stages of growth. Unwanted competition from airborne spores or bacteria can hinder mushroom growth. Additionally, pinning, the formation of mushroom pins, is a tricky stage that requires careful control of carbon dioxide concentration, temperature, light, and humidity to trigger fruiting.
