Never eat a wild mushroom identified only from a website, a book or an app. Have every find checked in person by an expert, such as a mycological society.
Identification
Lentinula edodes has a convex to flattened cap 5–15 cm across, light to dark brown, often with whitish fibrous scales towards the margin and, in some cultivated forms grown in dry air, a cracked surface (sold as flower shiitake). The gills are white to cream and become slightly serrated at the edge with age. The stem is tough and fibrous, central or off-centre, and is usually removed before cooking or used for stock.
The spore print is white. The flesh is white and firm, with the characteristic shiitake aroma due largely to the sulphur compound lenthionine, which intensifies when the mushroom is dried and rehydrated. Shiitake is classified in the Omphalotaceae, the same family as the jack-o'-lantern mushrooms.
Habitat and ecology
Shiitake is a white-rot decomposer of dead broadleaf trees, especially oaks and related species of the beech family, in the forests of China, Japan, Korea and parts of Southeast Asia. In the wild it fruits mainly in spring and autumn after rain. It does not grow wild in Europe or the Americas, where it is known only from cultivation and occasional escapes on logs.
Uses and importance
Shiitake is a staple of East Asian cuisine, used fresh in stir-fries, soups and hot pots, and dried to make rich broths such as Japanese dashi. Drying concentrates its umami taste. Fresh shiitake should be cooked thoroughly.
Research has focused on lentinan, a beta-glucan from the fruit body that has been studied in laboratory and animal experiments and in clinical studies in Japan as an injected adjunct in cancer therapy, and on eritadenine, which lowered cholesterol in animal studies. These results apply to purified compounds and specific study conditions, not to eating shiitake or taking supplements. In the EU, mushroom supplements are regulated as food, and health claims may only be used if authorised under Regulation (EC) No 1924/2006. Consult a doctor before using mushroom supplements alongside medication.
Cultivation
Traditional cultivation uses freshly cut hardwood logs, usually oak, drilled and inoculated with dowel or sawdust spawn and kept shaded and moist; logs begin fruiting after 6–18 months and can produce for several years. Modern production uses supplemented hardwood sawdust blocks, which are sterilised, inoculated and incubated for several weeks until the surface turns brown (browning). Fruiting is induced by a cold or soaking shock and occurs at about 12–20 °C depending on the strain. Shiitake is more demanding than oyster mushrooms but well suited to forest farming and specialty farms.
Safety and edibility
Shiitake is a good edible when cooked thoroughly. Eating raw or undercooked shiitake can cause shiitake dermatitis, an itchy rash of whip-like red streaks on the skin that typically appears one to two days later and is attributed to lentinan. Anyone who develops a rash or other reaction should see a doctor. Growers can develop respiratory allergy to the spores.
Shiitake is not collected wild in Europe. Anyone finding brown mushrooms on wood should never eat them based on a website or photo: identification must be confirmed in person by an expert, as deadly species such as Galerina marginata grow on wood too.
If you suspect mushroom poisoning, call 999 in an emergency or NHS 111 for urgent advice straight away, even before symptoms appear, and keep the remains of the mushrooms.
In the UK
Shiitake is not a wild species in the UK but is widely sold fresh and dried, and a number of British growers produce it indoors on sawdust blocks and outdoors on logs. Log cultivation with oak or other hardwoods suits the British climate.
The British Mycological Society recommends cultivating only on land where you have permission and avoiding outdoor cultivation of non-native species where possible; follow its advice on ventilation too, as spores can cause allergies. Eating raw or undercooked shiitake can cause shiitake dermatitis in some people.