Shiitake, Japanese forest mushrooms, are one of the Orient’s most exotic and delicious foods. Shiitake’s delicate, yet wild, woodsy taste adds a gourmet flair to almost any dish. Moreover, all eight amino acids are present in a ratio similar to the “ideal” protein for human nutrition. Shiitake are rich in the amino acids leucine and lysine, which are deficient in many grains. Shiitake are also a good source of B vitamins, including the ever-elusive B12. (Vitamin B12 is synthesized solely by bacteria and fungi and is not available from vegetables.) It is, however, shiitake’s medicinal possibilities that are getting worldwide attention. In the last two decades, scientists have isolated substances from shiitake that may play a role in the cure and prevention of modern civilisation’s dreaded illnesses: heart disease, cancer and AIDS.
Biologists consider shiitake and other mushrooms to be fungi, a group of primitive plants. Since they have no green pigments (chlorophyll), they cannot make food from sunlight as other plants, but must live by eating plants or animals. Shiitake’s favourite food is dead hardwood trees. The word “shii” is derived from the shii tree (Quercus cuspidate), an oak of central and southern Japan upon which shitake most often grow. “Take” means mushroom in Japanese (it is repetitious to say “shiitake mushroom”).
The part of shiitake that we eat, the fleshy cap, is actually a primitive reproductive structure. You may have noticed a grey or beige powder on the undersurface of opened mushrooms. These are billions of microscopic spores. Like sperm and eggs (ova) of animals, the spores are sex cells. Mushroom spores move about the forest with the help of wind and rain. When two compatible spores get together, they fuse their cytoplasm and genetic material and, if food is available, grow into a new mushroom. This new plant is a white filamentous subterranean growth called a mycelium. In the case of shiitake, mycelium grows inside the log, using its powerful enzymes to change wood into food. After a period of time, environmental stresses such as food depletion or temperature and humidity changes cause the mycelium to form a reproductive structure-the mushroom-and the cycle is complete.
Left to their own devices, shiitake would probably rather reproduce by the sexual cycle outlined above. However, to insure crop quality and consistency, shiitake growers inoculate their logs with the mushroom mycelium rather than spores. The so-called vegetative (asexual) method begins by growing shiitake mycelium on wood chips, paper disks or “enriched” sawdust. Shiitake cultivators then insert these “spawn” into holes or cuts made in hardwood logs.
In early fall, as trees shed their leaves in preparation for a dormant winter, the carbohydrate level in the tree trunk rises, making an ideal food for shitake growth. When about ten percent of the leaves have fallen, shiitake growers fell trees and cut them into three-foot logs. Next, about twenty to twenty-five evenly spaced holes are drilled into each log. Then wood chips (plug spawn) are hammered into the holes. When sawdust spawn are used, they are placed in holes using a special transfer tool. In both cases, the holes are sealed with wax.
After the logs are inoculated, they are carried into a pine forest and placed in a spot where there is an ideal balance of sunlight and shade. Usually, by the following fall, the shiitake mycelium has completely penetrated the logs, and, with seasonal temperature changes, mushrooms begin to push through the bark.
From just one inoculation, logs can be expected to produce crops of shiitake every fall and spring for three to five years, until the logs are completely decayed. The variety of shiitake called donko, are superior in both flavour and medicinal qualities to the variety called koshin. In their natural effort at self-preservation, donko shiitake produce a thick cap with strong viable spores to protect against harsh environmental conditions.
The harvesting time of shiitake is very important. If the mushroom is left on the log too long, it will completely open and shed its spores, producing a mushroom that is thin, flat, dark and lacking in vitality. According to Fusataro Taniguchi, the grower of Mitoku Macrobiotic premium sun-dried shiitake, donko shiitake (picked at the right time) should not be more than 70 percent open and should have thick, fleshy, slightly rounded caps. These cost more but are prized for their excellent flavour and healthfulness.
The “natural log” method of growing shiitake is still practiced by most of the Orient’s shiitake farmers. However, in the west, where shiitake farming is relatively new, the high-tech method of growing shiitake indoors under controlled conditions on “synthetic sawdust logs” (actually sawdust blocks) is used by approximately eighty percent of the large commercial growers.
The method of growing shiitake on sawdust logs is a direct outcome of the biotechnical revolution that has taken place since World War II. Drawing on the latest technology, exotic mushroom cultivators mix various nutrients into sawdust, which is then formed into a block, sterilized, and inoculated with shiitake mycelium. The blocks are then placed in semi-sterile growing rooms under “ideal conditions” to maximise mushroom growth.
The person most responsible for stimulating the current medicinal interest in shiitake was Japan’s Kisaku Mori, PhD. In 1936, Dr Mori established the Institute of Mushroom Research in Tokyo. Until his death in 1977, he worked with scientists from around the world to document the medicinal effects of shiitake. Using analytical techniques, Mori found shiitake high in many enzymes and vitamins that were not usually found in plants. Working for years with human subjects he discovered that shiitake was effective in treating a long list of ailments including high cholesterol, gallstones, hyperacidity, stomach ulcers, diabetes, vitamin deficiency, anaemia and even the common cold!
Mori’s work gained notoriety, particularly in Japanese medicinal circles, and, beginning in the 1960’s, scientists launched an extensive search to uncover the secret of shittake’s legendary healing powers. Their studies-about one hundred all all-focused on shiitake’s ability to rapidly lower serum cholesterol, as well as this mushroom’s potent antitumor, antiviral and antibiotic properties.
High levels of cholesterol in the blood have been linked to serious diseases such as arteriosclerosis and strokes, so investigators were excited in 1966 when they isolated a substance from shiitake that dramatically lowered blood cholesterol. This substance, now called eritadenine, was given to rats on a high-cholesterol diet. In just a few days the blood cholesterol level of the rats dropped 25 to 45 percent. Eritadenine has been associated with the water-soluble fibre of shiitake, but is action is even stronger when the whole mushroom is consumed. Studies with humans have shown that only three ounces of shiitake (5-6 mushrooms) a day can lower cholesterol 12 percent in a week.
“Many of the human diseases currently increasing throughout the world have no specific cures,” notes mycologist John Donoghue, co-author of Shiitake Growers Handbook. “Immune-system failure or dysfunction is a common element in cancer, viruses and immune-deficiency diseases,” says Donoghue. He and other scientists around the world contend that there is increasing evidence that the health-promoting compounds found in medicinal and edible fungi, including shiitake, stimulate the immune system.
Scientists now believe that a polysaccharide called lentinan and virus-like particles found in shiitake trigger the increased population of various serum factors associated with immunity and inflammation. These so called lymphokines, such as interferon and interleukin, stimulate the defence system, spurring the proliferation of phagocytes, including macrophages and other immune fighters that attack cancer cells, bacteria and viruses.
In addition to fighting cancer, inhibiting the growth of viruses and lowering cholesterol, shiitake have potent antibiotic effects against other organisms. A substance called cortinelin, a broad-spectrum antibacterial agent, which has been isolated from shiitake, kills a wide range of pathogenic bacteria. A sulphide compound extracted from shiitake has been found to have an effect against the fungus that causes ringworm and other skin diseases.
Shiitake or other healing mushrooms should be enjoyed as part of a daily diet. Dr Mori recommended four shiitake a day for the maintenance of health. However, when using shiitake as part of a therapeutic regimen, much larger doses are usually recommended.
The temperatures of cooking do not seem to destroy shiitake’s healing qualities. In addition, cooking greatly enhances the mushroom’s flavour. You can cook fresh shiitake in all the ways you are used to enjoying other mushrooms-in soups, stews, sauces and gravies. Shiitake are a flavourful addition to fried rice, noodles and stir-fried dishes. They are particularly delicious in tempura or when baked with a seasoning of Shoyu, mirin and fresh ginger. For a special treat brush shiitake caps with olive oil and grill three to four minutes.
To clean fresh shiitake simply wipe with a damp cloth or soft brush. They can also be rinsed under cold water and patted dry but be careful not to soak them as they will become soggy.
Dried shiitake are readily available in Oriental markets and natural food stores-now becoming more popular in supermarkets. Though the texture of reconstituted dried shiitake is not as tender as fresh the exquisite flavour is even more concentrated with drying. To reconstitute, submerge the dried shiitake in water for one to two hours, preferably overnight. After soaking, cut off and discard the tough stems and slice the caps. The soaking water makes a wonderful rich stock for soups, stews, sauces and gravies. Used with their soaking water and other ingredients such as carrots and greens, shiitake are a superb addition to miso soup.