Maitake aren’t simple. Among all major exotic mushroom varieties commercially cultivated in Japan, maitake are considered the most sensitive mushroom to environmental changes. One small change or brief issue with any of the cultivation settings, and suddenly no fruiting body appears or only deformed, stunted fruiting bodies emerge. Maitake are also a key source of consumer interest, with the highest natural vitamin D concentrations of any other commercial exotic mushroom variety, a high concentration of beta-glucan fibers and a variety of health benefits, including immunostimulation and cholesterol-lowering effects. The taste is also superb_emdash_meaty, fragrant, and pairing a rich umami flavor and unobtrusive texture.
 

Mixing Substrate

Sawdust from hardwood deciduous trees is necessary to cultivate maitake. Another commonly used medium for maitake cultivation in Japan is sawdust made from spent shiitake bolts after log cultivation has finished. Certain woods, such as black locust and magnolia, decrease yields of maitake if blended into the medium. The fineness of the sawdust used in cultivation is also very important, and using a grain size that is too fine will impact fruiting. Test for pH when filling. A pH of over 6.0 is the ideal breeding ground for bacillus bacteria, which will colonize the substrate otherwise. I recommend maintaining pH between 4.5~6 in maitake cultivation.
Nutrition supplements used in maitake cultivation include: wheat bran, rice bran, dried tofu lees (soy pulp from tofu production), and dried beer lees. Nutrition supplements should be mixed at a rate of roughly 10% of substrate weight, averaging about 200~250 grams per 2.5kg substrate block. Just like with shiitake, nutrition supplements should be thoroughly mixed in the mixer along with the water in order to get an even distribution. Likewise, aim for a total moisture content of between 60~63%. The standard for Japanese cultivation systems is to punch 4~6 holes 20 mm deep in the substrate to speed mycelial spread and aid the incubation process. This is done with the bagging machinery as bags are filled with mixed substrate.

Sterilization and Spawning

Maitake are very susceptible to infection. Even using sawdust that is too fresh leads to cases of “red water” where red water builds up inside of the bag and fruiting failure occurs. There are two types of autoclave commonly used to sterilize the substrate: normal pressure and high pressure autoclaves. Sterilization in bag cultivation is a very careful balancing act, thoroughly sterilizing the sawdust medium down all the way through without melting the bags. Bulk sterilization is also possible, but the infection rates are much higher and it is much more difficult and costly to control infection pressure, especially for sensitive varieties like maitake.

Substrate blocks quickly become a major contamination risk, particularly for mites and competitor molds. Over the course of several days harvesting a room, remove and dispose of all harvested substrate blocks as soon as possible. One method is to harvest in the morning, and then in the afternoon remove old substrate blocks. As only the top of the bag is cut off during maitake cultivation, the rest of the bag remains and commercial maitake growers use an automated machine that removes the rest of the plastic bag and grinds the spent substate back into a powdered form for efficient and easy transport.

Maitake can only deliver one flush in bag cultivation systems. However, it is possible to bury spent maitake substrate blocks outside in a thin layer of soil, after which they will fruit again. This is only possible in the cases where spent shiitake logs have not been used in the substrate, and the substrate is all fresh sawdust. Additionally, the most appropriate window for this is between May and June in Japan (the end of spring and through the early summer rainy season). Only spots without direct sunlight and with good airflow and breezes are appropriate. Forests and certain types of agricultural fields are possible candidates. If done properly, the spent substrate blocks will fruit again in September or October, with up to a 500-gram second flush.

Outdoor cultivation like this carries a number of other challenges. Foremost is the need to set up barriers to protect the fruiting bodies from coming into contact with rain once they begin to emerge but have not yet reached their mature state. Typically, this form of outdoor cultivation yields 200~300-gram harvests, which in ideal locations and properly managed conditions, can continue for 2~3 years, for a total of 4 flushes from the original substrate block. The maitake raised from outdoor cultivation of spent substrate blocks has a good reputation for premium taste and quality as well, so for mushroom growers who have suitable land, or who can sell to farmers and other landowners, this represents a potential source of income from spent substrate blocks.

Spent maitake substrate is a good soil conditioner that can be sold to local farmers. It improves the water retention of soil, and has a probiotic effect, increasing the diversity of soil microbiota and improves the efficiency of chemical fertilizers. Studies in Japan have found that spent maitake substrate also has good yields for lion’s mane production in a 50% fresh sawdust 50% spent maitake substrate mix, which can also be used for oyster mushroom production. In such cases, spent maitake substrate must be quickly ground and separated from bags, then at least partially dried in the sun before mixing. Ensure proper settings on autoclave as well, as improper sterilization has a higher contamination risk when reusing old substrate. Ensure the spent mushroom substrate on the farm is isolated from the rest of growing facilities, and if possible, downwind.