Ginkgo nuts are the seeds of the ginkgo tree. The white shells and thin outer skins are removed before cooking. Canned nuts are shelled, skinned and parboiled. Relatively high in vitamin C and carotene, ginkgo nuts appear in nabe, stir-fried, and deep-fried dishes.
Ginkgo (Ginkgo biloba; in Chinese and Japanese, pinyin romanization: yín xìng, Hepburn romanization: ichō or ginnan), also spelled gingko and also known as the maidenhair tree, is a unique species of tree with no close living relatives. The ginkgo is a living fossil, recognisably similar to fossils dating back 270 million years. Native to China, the tree is widely cultivated and was introduced early to human history. It has various uses in traditional medicine and as a source of food.
Ginkgo has long been cultivated in China; some planted trees at temples are believed to be over 1,500 years old. The first record of Europeans encountering it is in 1690 in Japanese temple gardens, where the tree was seen by the German botanist Engelbert Kaempfer. Because of its status in Buddhism and Confucianism, the ginkgo is also widely planted in Korea and parts of Japan; in both areas, some naturalization has occurred, with ginkgos seeding into natural forests.
In some areas, most intentionally planted ginkgos are male cultivars grafted onto plants propagated from seed, because the male trees will not produce the malodorous seeds. The popular cultivar ‘Autumn Gold’ is a clone of a male plant.
Ginkgos adapt well to the urban environment, tolerating pollution and confined soil spaces. They rarely suffer disease problems, even in urban conditions, and are attacked by few insects. For this reason, and for their general beauty, ginkgos are excellent urban and shade trees, and are widely planted along many streets.
Ginkgos are also popular subjects for growing as penjing and bonsai; they can be kept artificially small and tended over centuries. Furthermore, the trees are easy to propagate from seed.
The ginkgo leaf is the symbol of the Urasenke school of Japanese tea ceremony. The tree is the national tree of China, and is the official tree of the Japanese capital of Tokyo, and the symbol of Tokyo is a ginkgo leaf.
The nut-like gametophytes inside the seeds are particularly esteemed in Asia, and are a traditional Chinese food. Ginkgo nuts are used in congee, and are often served at special occasions such as weddings and the Chinese New Year (as part of the vegetarian dish called Buddha’s delight). In Chinese culture, they are believed to have health benefits; some also consider them to have aphrodisiac qualities. Japanese cooks add ginkgo seeds (called ginnan) to dishes such as chawanmushi, and cooked seeds are often eaten along with other dishes.
When eaten in large quantities or over a long period, especially by children the gametophyte (meat) of the seed can cause poisoning by 4′-O-methylpyridoxine (MPN). MPN is heat stable and not destroyed by cooking. Studies have demonstrated the convulsions caused by MPN can be prevented or terminated with pyridoxine.
Some people are sensitive to the chemicals in the sarcotesta, the outer fleshy coating. These people should handle the seeds with care when preparing the seeds for consumption, wearing disposable gloves. The symptoms are allergic contact dermatitis or blisters similar to that caused by contact with poison ivy. However, seeds with the fleshy coating removed are mostly safe to handle.