Japan is known for its unique and highly prized chestnut mushrooms, which are often referred to as "mushroom mushrooms" due to their distinct shape and rich flavor. These mushrooms are extremely popular among Japanese consumers, frequently given as gifts, and have driven the development of large-scale industrial cultivation. In some areas near vegetable markets, air-conditioned mushroom farms allow customers to personally pick two large fresh chestnut mushrooms and place them in a small bamboo basket covered with plastic wrap. Each basket typically weighs around 1 kilogram, with gray-black varieties priced at approximately 2,300 yen per basket and white ones at about 2,700 yen. This high price reflects their status as premium gift items, while regular edible chestnut mushrooms are cheaper but of lower quality.
Industrialized production has significantly boosted Japan’s chestnut mushroom output, reaching over 10,000 tons in 1997. However, demand still exceeds supply, with annual consumption estimated at around 20,000 tons. One notable example is a farm in Gunma Prefecture, where an investor spent about 20 million yuan in less than 1,000 square meters of space, employing five Nepalese workers to produce fresh mushrooms daily. The farm produces about 1,000 kg of mushrooms per day, valued at around 120,000 yuan per day, leading to annual sales of 24 million yuan. The investment was recouped within two years.
The cultivation techniques used on this farm include a mix of broad-leaved wood chips, particularly beech, which is considered the best for chestnut mushroom growth. A small percentage of coniferous wood shavings can also be added without affecting yield. Adding up to 30% of broad-leaved tree debris or other substitutes is acceptable, and including 20% soil in the substrate helps promote fruit body development. The particle size of the wood chips plays a key role in mycelial growth and yield, so adding 30-40% coarse wood chips (pulverized into pea-sized pieces) ensures good results.
Corn flour is the most suitable supplement, followed by bran. Using a 1:2 ratio of bran to corn flour improves yield compared to using either alone. Litchi chinense used as a pouch material alone produced low yields, but when mixed with beech wood chips, it matched the performance of eucalyptus wood chips. Additionally, mixing 20-30% old strains that had previously produced chestnut mushrooms increased yield by 5-10%, possibly due to residual bacterial activity, though further research is needed.
The cultivation process involves mixing sawdust and supplements in a volume ratio of 10:1 to 10:2.5, with dry materials mixed at a weight ratio of 10:2 to 10:3.5. Wood chips should be fine if supplements are added, and more supplements may be needed when coniferous wood chips are included. The medium must contain 50-55% moisture, ideally when squeezed by hand, water should just begin to drip from the fingers. For Maitake mushrooms, 64% moisture is optimal.
In Japan, square polypropylene bags with sterilized filter membranes are commonly used. Each bag is filled with 2.5-2.7 kg of wet material and has six 15-20 mm holes. The bags are 20 cm wide, 12 cm thick, and 15 cm tall, with the top 3-4 cm below the filter membrane. In winter, the bags are stored in the culture room beforehand to prevent damage. The bagging cycle takes 60-70 days.
For bottle cultivation, each 1-liter bottle is filled with about 600 g of culture medium, depending on the type of wood chips and grain thickness. The medium should not be packed too tightly to avoid malformed fruit bodies. Plastic bottles take 45-55 days to grow.
Sterilization is done at normal pressure (100°C) or via autoclaving at around 120°C. After cooling to 25°C, the medium is inoculated. The inoculation chamber is kept under positive pressure with filtered air, and all tools are disinfected with alcohol or flame sterilization. Each bag is inoculated with 20 bags per bottle, and 40-50 bottles per batch.
After inoculation, the bag mouth is sealed, leaving 5 cm of space above the material to ensure proper ventilation. The culture room temperature should be maintained at 22-23°C. If not ventilated, the mycelium may become weak due to excessive respiration, leading to a condition called “boring bacteria.†High humidity (>70%) can cause mold, so proper ventilation is essential, with CO₂ levels not exceeding 0.3%.
Lighting is crucial for the formation of primordia. During the first 35 days, light should be avoided to prevent browning of the mycelium. After that, 50 lux of light is ideal to stimulate primordium formation. Unlike some mushrooms, chestnut mushrooms do not require sporangia, but consistent growth is challenging. Proper ventilation and temperature control during the late germination stage help promote uniform primordium development.
After 35-40 days of culture, the mycelium begins to form bulges, which turn black into primordia after 7 days. When water droplets appear on the primordia, it's time to move them to the mushroom room. The key to producing high-quality mushrooms lies in the primordium's state when transferred, not just the conditions in the mushroom room. The primordium should be in the early stages of differentiation, with a rough surface but no signs of hypertrophy.
Chestnut mushrooms tend to form primordia quickly, which can lead to nutrient depletion and slow mushroom growth. To delay primordium formation and increase yield, yellow light is used. This method can delay formation by 20 days, increasing yield by 15-20%.
During the fruiting phase, the mushroom room must maintain a temperature of 18-22°C, humidity of 85-95%, and illumination of 200-500 lux. Airflow should be at least 0.3 m/s. After moving the bags into the room, the plastic film is cut in a cross shape, and the lid is removed for bottled mushrooms. Carbon dioxide levels must stay below 1.5‰; higher levels result in thin, funnel-shaped mushrooms.
Temperature stability is critical. Sudden changes can halt primordium development. Chestnut mushrooms are sensitive to low temperatures (<8°C), which can stop growth even after temperature returns to normal. Maintaining a constant temperature, slightly higher humidity, and no temperature fluctuations is essential.
High humidity is vital for mushroom development. Spraying systems are necessary in air-conditioned facilities to maintain 80-90% relative humidity.
In hot summers, the indoor temperature must be kept at 16°C with 90% humidity. A 9000 kcal/h chiller is used for an 80-square-meter room. Ventilation and cooling must be carefully managed to maintain optimal conditions.
Harvesting occurs when the cap becomes fan-shaped, with the color shifting from dark grey to light grey. The white layer under the cap develops, and the mushroom tilts upward. Mature mushrooms have a pale white color and emit a strong aroma. Harvesting typically takes 15-18 days, with the first harvest yielding 400-500 grams per bag.
After the first harvest, the spent substrate can be reused by burying the bags in soil, resulting in a second harvest of 250-300 grams per bag. Soil cultivation increases flavor and color, with a total bioconversion rate of 65-80%. The fruiting rate is highest when beds are cultivated before June, dropping significantly in July.
Spent substrates can also be placed in open areas with good ventilation and drainage. Covering the bags with leaves or straw helps retain moisture, allowing natural mushroom growth. While the quality is not as high as soil-cultivated mushrooms, this method makes use of waste materials, yielding 150-250 grams per bag.
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