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‘Yamaimo’: Japan’s slimy mountain yam

by

Special To The Japan Times

Japanese have a fondness for slippery, slimy food that people from other food cultures often find puzzling. Sticky nattō (fermented soy beans), mozuku and tororo konbu (two kinds of slimy seaweeds) may take some getting used to, but once you do they can be quite addictive. In addition, these slippery foods are packed with many healthy qualities, including fiber, minerals and antioxidants.

One of the most slimy, slippery foods of all is the yamaimo, also called yamatoimo, jinenjo or Japanese mountain yam (the botanical name is Dioscorea japonica). Both the yamaimo and its close relative, the nagaimo or Chinese yam (Dioscorea polystachya), can be cooked, but in Japan they are usually eaten raw after being finely julienned or grated. The cool, slippery texture is especially appreciated in the summer, it makes food slide down the throat nicely. It tends to be easy to digest, too. Grated yamaimo is served in hot or chilled miso soup, over soba noodles or mugimeshi (a mixture of rice and barley), with nattō or cubed raw tuna and other ingredients. You can even buy frozen, ready-to-eat grated yamaimo or nagaimo at convenience stores.

The sticky texture of yamaimo is also useful when cooking. It gives karukan, a traditional sponge cake-like confection from Kyushu, its elastic-yet-airy texture, and has a similar effect on okonomiyaki, the popular savory pancake from Osaka.

Yamaimo and nagaimo have long been considered healthy. In the Edo Period (1603-1868) the yamaimo was considered to be an aphrodisiac, and went by the name “mountain eel.” During this period men not only ate yamaimo, they added it — grated or sliced — to their bathwater to enhance their virility. Modern studies have confirmed that the humble root vegetables do have many beneficial qualities: they are high in soluble fiber, B vitamins and minerals, and in dried form they’re included in several traditional Eastern medicines.

Yamaimo and nagaimo can be used interchangeably in many dishes, but nagaimo has a more liquid, loose texture while yamaimo is stickier and paste-like. I prefer to use yamaimo in recipes that call for grated yam, and nagaimo in cooked dishes or finely julienned — plus it’s less expensive. Both are all about their texture rather than the taste. They are quite bland on their own, so you’ll need to add a sauce or soup with lots of flavor. If you’d like to experiment, try adding julienned nagaimo to a salad — the sticky texture helps the dressing cling better to the other vegetables.

Some people have a mild allergic reaction to yamaimo and nagaimo. If your skin gets itchy when you try to grate a piece, use protective gloves or just leave the skin on the part you’re touching. However, if they makes your lips or tongue itchy, you may want to stay away from both.

This week’s recipe is a classic that first became popular in the late 18th and early 19th centuries. Besides grated raw yamaimo, it contains two other highly popular “health foods” of the time: soba noodles and a raw egg yolk. It’s an unbeatable meal for anyone looking for an extra boost of energy, day or night. The key to pulling all the otherwise bland ingredients together is a good dipping sauce. Served well-chilled, it makes for a refreshing meal on a hot summer’s day.


Recipe: ‘Tororo soba’ (Soba noodles and yamaimo)

Serves 4

  • 200 grams dried soba noodles
  • 400 grams yamaimo (mountain yam)
  • 4 very fresh egg yolks
  • garnishes (green onion, myoga ginger or grated wasabi, nori seaweed)

For the sauce:

  • 500 ml water
  • 10-sq.-cm piece (about 5 grams) of konbu seaweed
  • 20 grams katsuobushi (bonito flakes)
  • 3 tablespoons soy sauce
  • 3 tablespoons mirin (rice wine vinegar)
  • 1 teaspoon sugar

Soak the konbu seaweed in a pan containing 500 ml of water for at least three hours.

Bring the water and konbu seaweed to a boil and take out the konbu. Add the bonito flakes, soy sauce, mirin and sugar, and let the sauce cool to room temperature. Strain through a fine-meshed sieve and refrigerate.

Bring a large pot of water to boil. Cook the soba noodles (it usually takes two to three minutes; if you’re not sure, test a strand after two minutes by biting into it — it should be just past al dente, firm yet cooked through). When cooked, drain the noodles, and rinse under running cold water. Plunge into a bowl of ice water to cool the noodles and firm up the texture. Drain well.

Grate the yamaimo. Finely chop the green onion, and grate the wasabi (or slice the myoga ginger). Shred the nori seaweed. Arrange the soba noodles in individual bowls topped with the yamaimo, egg yolk and garnishes. Serve the sauce in small bowls on the side. Pour the sauce over the noodles, mix well and enjoy.