Iwatake

What it is

Iwatake is the Japanese name for Umbilicaria esculenta, a lichen that grows on rock at high altitude in East Asia. Its accepted name is Umbilicaria esculenta (Miyoshi) Minks; an older name, Gyrophora esculenta Miyoshi, dates from 1893. In English it is called rock tripe or iwa-take.

The lichen body is attached to the stone by a single central holdfast, and its surface is often veined or wrinkled. Because it grows on exposed rock, the material that comes to the kitchen carries grit and dark residue from the stone, which is why cleaning comes before cooking.

Food use

The lichen is treated as a delicacy in China, Korea and Japan, where it is used in soups, dishes and salads. In Japan it is sold under the name iwatake; in Korea it is known as seok-i, and in China as 石耳.

The genus was also used as a food of last resort in North America. Accounts describe Native American and early settler use as famine food, which is a different role from the delicacy trade in East Asia.

Preparation and why it matters

One Chinese reference describes reconstituting the lichen in warm water, rubbing it to clean it, and rinsing it in cold water five or six times to remove the black residue and fine sand.

The lichen also contains bitter compounds, among them gyrophoric acid. Accounts of rock tripe describe extensive processing, typically soaking and repeated boiling, to reduce these compounds, and state that poorly processed lichen causes gastrointestinal distress. No account reviewed gives a tested time, temperature or water ratio for household use, so none is given here.

Safety and limits

The available accounts do not support a verdict that the lichen is safe to eat in any state, or that a specimen gathered in the wild is safe without preparation. Poorly prepared rock tripe has caused gastrointestinal illness. Identification of a specimen, and the choice between look-alikes, is a matter for a qualified lichenologist or mycologist; anyone gathering the lichen should follow a tested local preparation rather than a general guide.

Laboratory studies have isolated polysaccharides from the lichen and tested them on cells. Those studies do not test food use, dose or safety in people, and they are not evidence that eating the lichen is good for health.

Open questions

The accounts reviewed do not say how much gyrophoric acid boiling removes, how long a traditional soak lasts in a given kitchen, or how the Korean and Japanese methods differ from the Chinese method above. These are gaps in the record, not settled facts.