Sunday, October 9, 2011

True Yam(khamba alu) Cultivation

Yams(true yams / khamba alu)
Dioscorea Family (Dioscoreaceae): True Yams

Kingdom    : Plantae
                                                              (unranked)      : Angiosperms
                                                          (unranked)          : Monocots
                                                                  Order         : Dioscoreales
                                                                  Family        : Dioscoreaceae
                                                                  Genus         : Dioscorea
          Botanical Name : Dioscorea batatas 

Yams are often mistakenly called sweet potatoes, and vice versa, but they are two different vegetables. The true yam is the tuber of a tropical vine, and is not even distantly related to the sweet potato. Rarely found in US markets, the yam is a popular vegetable in Africa, Latin American and Caribbean markets. Generally sweeter than than the sweet potato, this tuber can grow over seven feet in length.

Subterranean tuber of a true yam (Dioscorea sp.), the third most important tropical root crop after cassava
yams ( khamba alu / deshi alu)

and sweet potatoes. The venation and shiny, heart-shaped leaves of true yams are unmistakable compared to those of sweet potatoes and other root crops.

Yam is the common name for some species in the genus Dioscorea (family Dioscoreaceae). These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania. There are many cultivars of yam.

The sweet potato (Ipomoea batatas) has traditionally been referred to as a yam in parts of the United States and Canada, but it is not part of the Dioscoreaceae family.

Top 10 Producers - 2008

------------------------------------------------------------------------------------------------------------------------------- 

(million metric ton)
 Nigeria          35.0
 Côte d'Ivoire   6.9
 Ghana             4.8
 Benin              1.8
 Togo               0.6
 Cameroon       0.3
 Colombia        0.2
 Brazil              0.2
 Haiti                0.2
----------------------------------------------------------------------------------------------------------
World Total   50.0


Although it is unclear which came first, the word yam is related to Portuguese inhame or Spanish ñame, which both ultimately derive from the Wolof word nyam, meaning "to sample" or "taste"; in other African languages it can also mean "to eat", e.g. yamyam and doya in Hausa or "to chew" in Dholuo language of the Luo of Kenya and Northern Tanzania.

Yam tubers
can grow up to 1.5 m (4.9 ft) in length and weigh up to 70 kg (154 lb) and 3 to 6 inches high. The vegetable has a rough skin which is difficult to peel, but which softens after heating. The skins vary in color from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the "meat". This substance ranges in color from white or yellow to purple or pink in mature yams.

Yams are a primary agricultural commodity in West Africa and New Guinea. They were first cultivated in Africa and Asia about 8000 BC. Due to their abundance and consequently, their importance to survival, the yam was highly regarded in Nigerian ceremonial culture and used as a vegetable offered during blessings.

Yams are still important for survival in these regions. The tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the wet season.

Preparation 

a Tongan farmer showing his yam
Africa

Yams of African species must be cooked to be safely eaten, because various natural substances in raw yams can cause illness if consumed. The most common cooking method in Western and Central Africa is by boiling, frying and roasting the yam.

Among the Akan of Ghana, boiled yam can be mashed with palm oil into eto (the yam version if what is known as matoke and served with eggs. The boiled yam can also be pounded with a traditional mortar and pestle to create a thick starchy paste known as Pounded Yam Iyan or Fufu which is eaten with traditional sauces such as egusi and palmnut soup.

Another method of consumption is to sun dry the raw yam pieces. When dry, the pieces turn a dark brown color. This is then milled to create a powder known as "elubo" in Nigeria. The brown powder can be prepared with boiling water to create a thick brown starchy paste known as amala which also goes with local soups and sauces.

In big cities and border towns in West Africa, fried yam and pepper sauce is a popular street food and has a similar position as french fries and ketchup elsewhere. Yam balls  has also gained some popularity in contemporary West African cuisine.

The Philippines
In the Philippines, the purple ube species of yam (Dioscorea alata), is eaten as a sweetened dessert called "ube halaya", and is also used as an ingredient in another Filipino dessert, halo-halo.

Vietnam
In Vietnam, the same purple yam is used for preparing a special type of soup canh khoai mỡ or fatty yam soup. This involves mashing the yam and cooking it until very well done.

Indonesia
In Indonesia, the same purple yam is used for preparing desserts. This involves mashing the yam and mixing it with coconut milk and sugar.

Japan
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.

In Japan, the 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.

India
In central parts of India, the yam (or Garadu / ghar alu / khamba alu / deshi alu) is prepared by being
finely sliced, seasoned with spices and deep fried. In southern parts of India, the vegetable is a popular accompaniment to fish curry. In Assam, it is known as Kosu  and is normally boiled, mashed and lightly seasoned with salt.

Also eaten in India, Dioscorea alata, a purple-pigmented species, is known as ratalu or violet yam.

The West
'Yam powder' is available in the West from grocers specializing in African products, and may be used in a similar manner to instant mashed potato powder, although preparation is a little more difficult because of the tendency to form lumps. The 'yam powder' is sprinkled onto a pan containing a small amount of boiling water, and stirred vigorously. The resulting mixture is served with a heated sauce, such as tomato and chili, poured onto it. To avoid lumps forming, the powder and the water are mixed before putting on the heat, then stirred continuously as the mixture is heating.

Cultural aspects

Nigeria and Ghana
A Yam Festival is usually held in the beginning of August at the end of the rainy season. A popular holiday in Ghana, the Yam Festival is so named because yam is the most common food in many African countries. Yams are the first crops to be harvested. People offer yams to gods and ancestors first, before distributing them to the villagers. This is their way of giving thanks to the spirits above them.

New Yam Festival (Igbo in South-East, Nigeria)
The New Yam Festival consists of prayers and thanks for the years past. Yam is the main agricultural crop of the Igbos, Idomas, and Tivs. It is the "staple" food of the Igbo people. The New Yam Festival, known as Orureshi in Owukpa in Idoma west and Ima-Ji, Iri-Ji or Iwa Ji in Igbo land is a celebration depicting the prominence of yam in the social and cultural life. The festival is very promiment among all the major tribes in Benue state, mainly around August.

Yam  feast is  held to honor the earth goddess and the ancestral spirits of the clan. New yams could not be eaten until some had first been offered to these powers.

Elsewhere
Historical records in West Africa and of African yams in Europe date back to the 16th century. Yams were taken to the Americas through precolonial Portuguese and Spanish on the borders of Brazil and Guyana, followed by a dispersion through the Caribbean.
In many societies yams are so important that one can speak of a 'yam civilization'. 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.

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 growing of yam. People of ancient times worshiped the yam. Olhuala is a type of local yam that is a staple food in the Maldives.

On the Japanese island of Rishiri, yams and yam products are regarded as a folk remedy for the treatment of impotence, possibly because of the vegetable's high vitamin E content, but likely because of its evocation of virile phallic imagery, according to the common folk medicine theory of sympathetic medicine.
 

 Major cultivated species

Dioscorea rotundata and D. cayenensis
Dioscorea rotundata, the "white yam", and Dioscorea cayenensis, the "yellow yam", are native to Africa. They are the most important cultivated yams. In the past they were considered two separate species but most taxonomists now regard them as the same species. There are over 200 cultivated varieties between them. The Kokoro variety is important in making dried yam chips.

They are large plants; the vines can be as long as 10 to 12 meters (33 to 39 ft). The tubers most often weigh about 2.5 to 5 kilograms (5.5 to 11 lb) each but can weigh as much as 25 kilograms (55 lb). After 7 to 12 months growth the tubers are harvested. In Africa most are pounded into a paste to make the traditional dish of "pounded yam" .

D. alata

Dioscorea alata, called "water yam", "winged yam" and "purple yam", was first cultivated in Southeast

Asia. Although not grown in the same quantities as the African yams, it has the largest distribution world-wide of any cultivated yam, being grown in Asia, the Pacific islands, Africa, and the West Indies . In the United States it has become an invasive species in some Southern states.
In the Philippines it is known as "ube" and is used as an ingredient in many sweet desserts. In Vietnam, it is called khoai mỡ and is used mainly as an ingredient for soup. In India, it is known as ratalu or violet yam 
or khamba alu or deshi alu . In Hawaii it is known as uhi.

Uhi was brought to Hawaii by the early Polynesian settlers and became a major crop in the 19th century when the tubers were sold to visiting ships as an easily stored food supply for their voyages .

chinese yam(khamba alu)
D. opposita
Dioscorea opposita, "Chinese yam", is native to China. The Chinese yam plant is somewhat smaller than the African, with the vines about 3 meters (10 feet) long. It is tolerant to frost and can be grown in much cooler conditions than other yams. It is now grown in China, Korea, and Japan.

It was introduced to Europe in the 19th century when the potato crop there was falling victim to disease, and is still grown in France for the Asian food market.

The tubers are harvested after about 6 months of growth. Some are eaten right after harvesting and some are used as ingredients for
chinese yam(khamba alu plant)

other dishes, including noodles, and for traditional medicines .

D. bulbifera

Dioscorea bulbifera, the "air potato", is found in both Africa and Asia, with slight differences between those found in each place. It is a large vine, 6 meters (20 ft) or more in length. It produces tubers; however the bulbils which grow at the base of its leaves are the more important food product. They are about the size of potatoes (hence the name "air potato"), weighing from 0.5 to 2 kilograms (1.1 to 4.4 lb).

Some varieties can be eaten raw while some require soaking or boiling for detoxification before eating. It is not grown much commercially since the flavor of other yams is preferred by most people. However it is popular in home vegetable gardens because it produces a crop after only four months of growth and continues producing for the life of the vine, as long as two years. Also the bulbils are easy to harvest and cook .

In 1905 the air potato was introduced to Florida and has since become an invasive species in much of the state. Its rapid growth crowds out native vegetation and is very difficult to remove since it can grow back from the tubers, and new vines can grow from the bulbils even after being cut down or burned .

D. esculenta

Dioscorea esculenta, the "lesser yam", was one of the first yam species cultivated. It is native to Southeast Asia and is the third most commonly cultivated species there, although it is cultivated very little in other parts of the world. Its vines seldom reach more than 3 meters (10 feet) in length and the tubers are fairly small in most varieties.

The tubers are eaten baked, boiled, or fried much like potatoes. Because of the small size of the tubers, mechanical cultivation is possible; which, along with its easy preparation and good flavor, could help the lesser yam to become more popular in the future .

D. trifida

Dioscorea trifida, the "cush-cush yam", is native to the Guyana region of South America and is the most important cultivated New World yam. Since they originated in tropical rain forest conditions their growth cycle is less related to seasonal changes than other yams. Because of their relative ease of cultivation and their good flavor they are considered to have a great potential for increased production .

D. dumetorum
Dioscorea dumetorum, the "bitter yam", is popular as a vegetable in parts of West Africa; one reason being that their cultivation requires less labor than other yams.

The wild forms are very toxic and are sometimes used to poison animals when mixed with bait. It is said that they have also been used for criminal purposes .

Nutritional value

Yam provides around 110 calories per 100 grams of product. Yam is high in vitamins C and B6, potassium, manganese and dietary fiber while being low in saturated fat and sodium. A product that is high in potassium and low in sodium is likely to produce a good potassium-sodium balance in the human body, and so protects against osteoporosis and heart disease.

Yam products generally have a lower glycemic index than potato products, which means that they will provide a more sustained form of energy, and give better protection against obesity and diabetes.
It is also known to replenish fast-twitch fibers and West Indians use it as a way of recovering after sprinting.

Other uses of the term yam

n the United States, sweet potato (Ipomoea batatas), especially those with orange flesh, are often referred to as "yams." In the United States, firm varieties of sweet potatoes were produced before soft varieties. When soft varieties were first grown commercially, there was a need to differentiate between the two. African slaves had already been calling the soft sweet potatoes "yams" because they resembled the yams in Africa. Thus, soft sweet potatoes were referred to as yams to distinguish them from the firm varieties. Sweet potatoes labeled as "yams" are widely available in markets that serve Asian or Caribbean communities.
Today the U.S. Department of Agriculture requires sweet potatoes labeled with the term "yam" to be accompanied by the term "sweet potato."

In New Zealand "yam" sometimes refers to the oca (Oxalis tuberosa). "Kumara" refers to the sweet potato.
The corm of the konjac is often colloquially referred to as a yam, although it bears no marked relation to tubers of the genus Dioscorea.

In Malaysia and Singapore, "yam" is used to refer to taro.


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