Yam

? Dioscorea (Yam)
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Liliopsida Order: Dioscoreales Family: Dioscoreaceae Genus: Dioscorea L.

Yam is the common name for members of the genus Dioscorea (family Dioscoreaceae). There are more than 150 different varieties of yam. Some species are cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania.

The word yam comes from Portuguese inhame or Spanish ñame, which both ultimately derive from the Wolof word nyami, meaning "to eat". They are used in a similar fashion to potatoes, and are sometimes called a potato substitute, though in areas where yams are grown, potatoes are the newer vegetable.

Yam tubers can grow up to seven feet (approx. two meters) in length and weigh up to 150 pounds (68 kg). The yam has a rough skin which is difficult to peel, but which softens after heating. Yam skins vary in color from dark brown to light pink. The majority of the yam is composed of a much softer substance known as the "meat". This substance ranges in color from white to bright orange in ripe yams.

Yams are a primary agricultural commodity in West Africa and New Guinea. They were first cultivated in Africa and Asia about 8000 B.C.E., probably because they were able to flourish in environments where growing leafy vegetables and keeping livestock was difficult. To this day, the yam tuber remains crucial to survival in the region; it can be stored for four to six months without refrigeration, which makes it a valuable resource for the yearly period of food scarcity at the beginning of the wet season.

Yams are used as food plants by the larvae of some Lepidoptera species including Palpifer sordida.

File:Vanuatu marché igname.JPG

Yams at Port-Vila market (Vanuatu)

Preparation

Tongan farmer showing off his prize yams

Yams of African species must be cooked to be safely eaten because various natural substances in raw yams can cause illness if consumed. Preparing some species of yam is a time-consuming process, involving days of pounding, leaching, and boiling to remove the toxins. Yams may be served fried, boiled or pounded into a paste. In the Philippines, the purple ube variety of yam (Dioscorea alata, also known in India as ratalu or violet yam) is eaten as a sweetened dessert called halaya, and is also an ingredient in another Filipino dessert, halo halo.

An exception to the cooking rule is the Japanese mountain yam (Dioscorea opposita), known as nagaimo or yamaimo depending on the root shape. It 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.

Yams and sweet potatoes

In the United States, sweet potatoes (Ipomoea batatas) are often referred to as "yams". Sweet potatoes labeled (incorrectly, according to some) as "yams" are widely available in U.S. grocery stores. True yams are only found in specialty markets such as those that serve Asian or Caribbean communities.

Top Yam Producers - 2005 (million metric ton)
Nigeria	26.6
Ghana	3.9
Côte d'Ivoire	3.0
Benin	2.3
Togo	0.6
Columbia	0.3
World Total	39.9
Source: UN Food & Agriculture Organisation (FAO)[1]

In contrast, people in New Zealand use the word "yam" to refer to the oca (Oxalis tuberosa), and the word "kumara" to refer to the sweet potato.

Yam culture

The coming of the yams (one of the numerous versions from Maré in Pene Nengone (Loyalty Islands - New Caledonia) [2]

In many societies yams are so important that one can speak of a yam culture. Growing the tuber is associated with magic; the best ones must be given to the chief or king; there is a series of myths connected to a divine origin; a farmer may gain a lot of prestige by growing the largest or longest yam; etc.

• Micronesia, for example Pohnpei.
• Melanesia, for example Vanuatu, Papua New Guinea.
• Polynesia, west Polynesia only, like Samoa, Tonga. In Tonga the ancient names of the months of the year and the names of the days of the moon-month were all geared towards the yam culture.

Selected species

• Dioscorea alata - ube, purple yam, water yam
• Dioscorea altissima - dunguey
• Dioscorea bulbifera - air yam, air potato
• Dioscorea cayenensis - yellow Guinea yam
• Dioscorea dumetorum - bitter yam
• Dioscorea elephantipes - Hottentot yam
• Dioscorea esculenta - lesser yam, potato yam
• Dioscorea floridana - Florida yam
• Dioscorea hispida - intoxicating yam
• Dioscorea opposita (syn. Dioscorea batatas, Dioscorea japonica, Dioscorea polystachya, Dioscorea oppositifolia) - Chinese yam, Japanese mountain yam, Korean yam, yamaimo
• Dioscorea polygonoides - mata gallina
• Dioscorea preussii - Preuss' dioscorea
• Dioscorea rotundata - Guinea yam
• Dioscorea sansibarensis - Zanzibar yam
• Dioscorea trifida - Indian yam

Dioscorea bulbifera

Dioscorea bulbifera is a species of yam known as the air potato. It is a perennial vine with broad leaves and two types of storage organs. The plant forms bulbils in the leaf axils of the twining stems, and tubers beneath the ground. These tubers are like small, oblong potatoes, and they are edible and cultivated as a food crop, especially in West Africa. The tubers often have a bitter taste, which can be removed by boiling. They can then be prepared in the same way as other yams, potatoes, and sweet potatoes. The air potato is one of the most widely-consumed yam species.

The air potato plant is native to Africa and Asia. In other areas of the globe, notably Florida, it is an invasive species. It is a quick-growing, large-leafed vine which spreads tenaciously and shades out any plants growing beneath it. The bulbils on the vines sprout and become new vines, twisting around each other to form a thick mat. If the plant is cut to the ground, the tubers can survive for extended periods and send up new shoots later.

Dioscorea opposita

Segment of a Dioscorea opposita tuber

Dioscorea opposita (also Dioscorea batatas, Dioscorea japonica, Dioscorea polystachya, Dioscorea oppositifolia, nagaimo, yamaimo, Chinese yam, Japanese mountain yam, Korean yam) is a type of yam (Dioscoreaceae) that may be eaten raw.

It is known as either nagaimo (kanji: 長芋; hiragana: ながいも) or yamaimo (kanji: 山芋; hiragana: やまいも) in Japanese, depending on root shape. In Chinese it is known as huái shān (淮山), shān yào (山药), or huái shān yào (淮山药).

Dioscorea opposita is an exception to the rule that yams must be cooked before consumption (due to harmful substances in the raw state). In Japanese cuisine, it 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.

Dioscorea opposita is used in the Japanese cold noodle dish tororo udon. The grated nagaimo is known as tororo (in Japanese). In tororo udon, the tororo is mixed with other ingredients that typically include tsuyu broth (dashi), wasabi, and green onions. Jinenjo (wild yam) is another variety of Japanese yam that is used as an ingredient in soba noodles.

The tuber is also used (often in dried form) in traditional Chinese medicine and Chinese herbology.

Dioscorea alata

A Piece of Cake Made With Ube.

Ube (or ubi) is the Tagalog word for purple yam (Dioscorea alata). In India, this vegetable is known as ratalu or violet yam or the Moraga Surprise. In the Philippines, ube is eaten as a sweetened dessert called halaya. Ube is also an ingredient in the fruity dessert halo halo, another popular Filipino dessert.

In botany, this species is also known by the names "water yam" and "winged yam".

History

Probably brought to the Philippines by settlers, the ube plant spread like a weed unknown to locals. It was discovered around the time of famine when people were desperate for food.

Ube is now used in a variety of desserts, as well as a flavour for ice cream, Swiss rolls, tarts, cookies, cakes, and pastries.

References

ISBN links support NWE through referral fees

• Consultative Group on International Agricultural Research (CGIAR), 1994, "A Breakthrough in Yam Breeding"[3]
• Consultative Group on International Agricultural Research (CGIAR), 2006, "Yam"[4]
• Kay, D.E., 1987, Root Crops, Tropical Development and Research Institute : London[5]
• O'Hair, S.K., 1990, "Tropical Root and Tuber Crops", p. 424-428. In: J. Janick and J.E. Simon (eds.), Advances in New Crops. Timber Press : Portland, OR.[6]
• Schultz, G.E., 1993, "Element Stewardship Abstract for Dioscorea bulbifera, Air potato", The Nature Conservancy[7]
• University of Connecticut(UC), 2006, "Dioscoreaceae"[8]
• White, L.D., 2003, Canoe Plants of Ancient Hawai'i, "Uhi"[9]

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