Difference between revisions of "Yam" - New World Encyclopedia
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==The yam plant== | ==The yam plant== | ||
− | Most yam species grow in the tropics and sub-tropics in areas with fairly heavy total annual rainfall but with a definate dry season. During the rainy season they produce one or more underground tubers to store food and water through the dry season. The tubers are thickened stems. At the end of the dry season they send out shoots which grow into vines which grow up into nearby trees and bushes. Many species grow bulbils, small tuber like growths, at the bases of their leaves. These can fall to the ground and produce new plants. Most yam plants have small flowers with one plant having only male or female flowers(Kay, 1987). | + | Most yam species grow in the tropics and sub-tropics in areas with fairly heavy total annual rainfall but with a definate dry season. During the rainy season they produce one or more underground tubers to store food and water through the dry season. The tubers are thickened stems. At the end of the dry season they send out shoots which grow into vines which grow up into nearby trees and bushes. Many species grow bulbils, small tuber like growths, at the bases of their leaves. These can fall to the ground and produce new plants. Most yam plants have small flowers with one plant having only male or female flowers (Kay, 1987). |
− | ==Cultivation== | + | ==Cultivation== |
+ | The tubers of most species of yam are poisonous to humans. A few are edible and some others can be made edible by various methods including soaking, boiling, and drying. People started to cultivate yams, rather than just digging up wild ones, as long as 10,000 years ago in both Africa and Asia; and some time later in the New World. | ||
− | + | The cultivation of yams is very labor intensive. Cultivated yams mostly do not produce seeds and so tubers or pieces of tuber must be planted in prepared soil, most often in mounds, to grow new plants. Some kind of framework or trellis must be provided to support the vines, unless they are grown next to trees or in fields previously planted with corn so the old stalks can provide support. At the begining of the dry season the vines die away and the tubers are ready to be harvested. They must be dug out by hand very carefully; if they are damaged they could spoil soon (Kay 1987). | |
− | + | Yams are a nutricious food providing [[carbohydrates]], some [[protein]], and minerals like [[phosphorus]] and [[potassium]]. Tubers can be stored as long a six months without refridgeration (CGAIR 2006). | |
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==Preparation== | ==Preparation== |
Revision as of 19:32, 20 August 2006
Dioscorea (Yam) | ||||||||||||
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Scientific classification | ||||||||||||
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Yams are members of the flowering plant genus Dioscorea. They are monocots, related to palms, grasses, and orchids. There are about 600 species of yams found around the world, mostly in the tropics. Some species of yam are cultivated for their edible tubers, for medicinal use, and for other uses. Yams remain an important food crop, especially in Africa.
In the United States sweet potatoes, Ipomoea batatas, are sometimes called "yams", although they are not closely related.
The yam plant
Most yam species grow in the tropics and sub-tropics in areas with fairly heavy total annual rainfall but with a definate dry season. During the rainy season they produce one or more underground tubers to store food and water through the dry season. The tubers are thickened stems. At the end of the dry season they send out shoots which grow into vines which grow up into nearby trees and bushes. Many species grow bulbils, small tuber like growths, at the bases of their leaves. These can fall to the ground and produce new plants. Most yam plants have small flowers with one plant having only male or female flowers (Kay, 1987).
Cultivation
The tubers of most species of yam are poisonous to humans. A few are edible and some others can be made edible by various methods including soaking, boiling, and drying. People started to cultivate yams, rather than just digging up wild ones, as long as 10,000 years ago in both Africa and Asia; and some time later in the New World.
The cultivation of yams is very labor intensive. Cultivated yams mostly do not produce seeds and so tubers or pieces of tuber must be planted in prepared soil, most often in mounds, to grow new plants. Some kind of framework or trellis must be provided to support the vines, unless they are grown next to trees or in fields previously planted with corn so the old stalks can provide support. At the begining of the dry season the vines die away and the tubers are ready to be harvested. They must be dug out by hand very carefully; if they are damaged they could spoil soon (Kay 1987).
Yams are a nutricious food providing carbohydrates, some protein, and minerals like phosphorus and potassium. Tubers can be stored as long a six months without refridgeration (CGAIR 2006).
Preparation
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 rotundata
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
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
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".
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.
Dioscorea esculenta
Dioscorea trifida
Dioscorea dumetorum
Dioscorea hispida
Dioscorea cayenensis
ReferencesISBN 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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