Yam (vegetable)
Japan

An exception to the cooking rule is the mountain yam (Dioscorea polystachya), known as nagaimo and can be further classified into ichōimo (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or yamatoimo (lit. Yamato yam; kanji: 大和芋), depending on the root shape.

Mountain yam is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution to neutralize irritant oxalate crystals found in their skin. The raw vegetable is starchy and bland, mucilaginous when grated, and may be eaten plain as a side dish, or added to noodles.

Another variety of yam, jinenjo, is used in Japan as an ingredient in soba noodles. In Okinawa, purple yams (Dioscorea alata) are grown. This purple yam is popular as lightly deep-fried tempura, as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream with the signature purple color. Purple yam is also used in other types of traditional wagashi sweets, cakes, and candy.
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