Harvesting and crop storage
To produce a high quality crop, it is important to use correct harvesting and storage conditions. Once mushroom formation has begun, shiitake often matures to a harvestable stage in 2 to 7 days. This makes daily harvesting necessary. With experience, growers can usually predict the periods of heaviest fruiting based on temperature and previous rainfall or watering.
The preferred stage for harvesting is just before the cap completely expands. The mushrooms are snapped off cleanly at the log surface and, in Japan, are placed in baskets. Although shiitake resists bruising, care should be taken to minimize damage because damaged mushrooms have less customer appeal and spoil more easily.
Fresh mushrooms intended for market should be stored refrigerated in trays with slots for ventilation. Mushrooms should not be frozen unless they are to be marketed in this form. Some buyers prefer dried shiitake for ease of storage and for their enhanced flavor characteristics. Heated forced air chambers are generally used for dehydration on a commercial scale. In commercial scale dehydration, shiitake is usually dried on racks at 30°C (86O F) initially, gradually increased 1° to 2°C (2° to 4°F) per hour to 50O C (122O F). They are then heated at 60O C for 1 hour. The final heating step develops popular flavor characteristics and gives the cap an attractive luster. Alternatively, shiitake is easily sun-dried.
Marketing shiitake
Consumer safety is an extremely important topic. If the cultivation method described here is followed carefully, most of the mushrooms found growing on inoculated logs should be shiitake. After observing the characteristics of shiitake, most people can easily recognize it. However, occasionally wild mushrooms will also grow on some logs. Because some wild mushrooms are poisonous, growers must be absolutely certain that the mushrooms intended for consumption are shiitake. Under no circumstances should growers mix in any wild mushrooms with their product.
There is no quick, safe method known to distinguish poisonous mushrooms from edible ones, other than positive identification of the mushroom in question. If unsure of the indentity of a mushroom, one should seek outside help. Often a local college or university will have a mycologist specializing in fungal taxonomy who may be able to identify mushrooms.
Once a reliable quality product exists, successful establishment and growth of an industry is dependent on market development and marketing procedures. Markets for shiitake already exist in the United States and, fortunately, during a temporary lack of a market, shiitake can be dried and stored. Because it generally is not available to them, local Oriental food stores and restaurants will probably be especially interested in obtaining fresh shiitake. Considerable room for development of new markets exists. When one can consistently produce and deliver quality mushrooms in sufficient quantity, inquiries can be made into the possibility of supplying mushrooms through grocery markets, distributors, or to food packaging companies for use in their products.
Other potential mushroom crops
The method of mushroom cultivation described here may be useful for other edible wood-rotting fungi. Mushrooms common in the Orient, often cultivated on logs using similar methods, include Auricularia auricula and A. polytricha (wood ear or ear fungus begins to fruit 2 to 3 mo. after inoculation); Pholiota nameko (“Nameko” requires more moisture); Pleurotus species including P. ostreatus (oyster mushroom); and Tremella fuciformis (white jelly fungus begins to fruit 2 to 4 mo. after inoculation).
Testing of logs from domestic tree species will be necessary to determine the optimal species for each fungus. Other edible wood-rotting fungi, including native species, might also be successfully cultivated using these methods. However, one should not attempt to cultivate potentially pathogenic fungi such as Armillariella mellea (the native “honey mushroom”) even if the mushrooms they produce are desirable. The infection that may spread to local trees and forests could be disastrous. Dutch-elm disease is caused by a fungus.
Summary and conclusions
A promising new industry for the United States is the production of shiitake on small diameter hardwood logs from currently non-commercial trees. Methods to cultivate shiitake on logs were developed in Japan. These methods may also be adapted to cultivating shiitake and other nonpathogenic edible wood-rotting mushrooms in the United States.
The cultivation method is not difficult but, to avoid contamination by competitive micro-organisms and to ensure optimal mushroom production, cultural practices must be carried out correctly. Logs are cut from live trees, aged, and then inoculated with an actively growing fungal culture. Once inoculated, logs are laid to favour fungal growth. After the fungus has colonized the logs, they are restacked to favor fruiting. Soaking logs in water may be used to stimulate the production of mushrooms.
Prior to marketing, storage of fresh shiitake is by refrigeration or shiitake may be dried. Current U.S. markets for shiitake are Oriental food stores and restaurants which purchase dried shiitake from Japan. Considerable room for market expansion exists in the United States for both fresh and dried shiitake.
Author: Gary F. Leatham. The author is a Research Microbiologist, USDA Forest Serv., Forest Prod. Lab:, P.O. Box 5130, Madison, WI 53705. The Laboratory is maintained in cooperation with the. Univ. of Wisconsin, Madison.
