Sweet potato

"Camote" redirects here. For the island group in the Philippines, see Camotes Islands.

Sweet Potato
Sweet potato in flower Hemingway, South Carolina
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Solanales
Family:	Convolvulaceae
Genus:	Ipomoea
Species:	I. batatas
Binomial name
Ipomoea batatas (L.) Lam.

The sweet potato (Ipomoea batatas) is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are an important root vegetable. The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally, but many are actually poisonous.

The sweet potato is only distantly related to the potato (Solanum tuberosum). The softer, orange variety is often called a yam in parts of North America, a practice intended to differentiate it from the firmer, white variety. The sweet potato is botanically very distinct from the other vegetable called a yam, which is native to Africa and Asia and belongs to the monocot family Dioscoreaceae. To prevent confusion, the United States Department of Agriculture requires sweet potatoes labeled as "yams" also be labeled as "sweet potatoes". In New Zealand English, the Māori term kūmara is commonly used.

The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of Ipomoea batatas are grown as ornamental plants; the name "tuberous morning glory" may be used in a horticultural context.

The plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose colour ranges between red, purple, brown and white. Its flesh ranges from white through yellow, orange, and purple.

Origin, distribution and diversity

File:Sweetpotato5162.jpg

Sweet potatoes in the field

Wild sweet potato (or kamote, as it is known there) in the Philippines

Sweet potatoes are native to Central America, and were domesticated there at least 5,000 years ago.

Austin (1988) postulated that the center of origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The 'cultigen' had most likely been spread by local people to the Caribbean and South America by 2500 BC. Zhang et al. (1998) provided strong supporting evidence that the geographical zone postulated by Austin is the primary center of diversity. The much lower molecular diversity found in Peru–Ecuador suggests this region should be considered as secondary center of sweet potato diversity.

The sweet potato was also grown before western exploration in Polynesia. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 AD, and current thinking is that it was brought to central Polynesia around 700 AD, possibly by Polynesians who had traveled to South America and back, and spread across Polynesia to Hawaii and New Zealand from there. It is possible, however, that South Americans brought it to the Pacific. The theory that the plant could spread by floating seeds across the ocean is not supported by evidence. Another point is that the sweet potato in Polynesia is the cultivated Ipomoea batatas, which is generally spread by vine cuttings and not by seeds.

Sweet potatoes are now cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth.

According to the Food and Agriculture Organization (FAO) statistics, world production in 2004 was 127,000,000 tonnes. The majority comes from China, with a production of 105,000,000 tonnes from 49,000 km². About half of the Chinese crop is used for livestock feed.

Per capita production is greatest in countries where sweet potatoes are a staple of human consumption, led by Papua New Guinea at 550 kg per person per year, the Solomon Islands at 160 kg, Burundi and Rwanda at 130 kg and Uganda at 100 kg.

About 20,000 tonnes (20,000,000 kg) of sweet potatoes are produced annually in New Zealand, where sweet potato is known by its Māori name, kūmara. It was a staple food for Māori before European contact.

In the U.S., North Carolina, the leading state in sweet potato production, provided 38.5% of the 2007 U.S. production of sweet potatoes. In 2007, California produced 23%, Louisiana 15.9%, and Mississippi 19% of the U.S. total.

The town of Opelousas, Louisiana's "Yambilee" has been celebrated every October since 1946. The Frenchmen who established the first settlement at Opelousas in 1760 discovered the native Atakapa, Alabama, Choctaw, and Appalousa tribes eating sweet potatoes. The sweet potato became a favorite food item of the French and Spanish settlers and thus continued a long history of cultivation in Louisiana.

Mississippi has about 150 farmers presently growing sweet potatoes on about 8,200 acres (33 km²), contributing $19 million dollars to the state's economy. Mississippi's top five sweet potato producing counties are Calhoun, Chickasaw, Pontotoc, Yalobusha, and Panola. The National Sweet Potato Festival is held annually the entire first week in November in Vardaman (Calhoun County), which proclaims itself as "The Sweet Potato Capital".

The town of Benton, Kentucky, celebrates the sweet potato annually with its Tater Day Festival on the first Monday of April. The town of Gleason, Tennessee, celebrates the sweet potato on Labor Day weekend with its Tater Town Special.

Recently, sweet potatoes have gotten a lot of media attention since actor American Matthew Morrison confessed in an interview for Details (Magazine) to go an a sweet potato diet before shootings.

Cultivation

Producers (in million tonnes) Data for year 2009
China	80.5
Nigeria	3.3
Uganda	2.7
Indonesia	1.88
Vietnam	1.32
Tanzania	1.31
India	1.1
Japan	1.0
World	106.5

The softer, orange-fleshed variety of sweet potato.

The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F), abundant sunshine and warm nights. Annual rainfalls of 750–1,000 mm (30–39 in) are considered most suitable, with a minimum of 500 mm (20 in) in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting, and it is not tolerant to water-logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor.

Depending on the cultivar and conditions, tuberous roots mature in two to nine months. With care, early-maturing cultivars can be grown as an annual summer crop in temperate areas, such as the northern United States. Sweet potatoes rarely flower when the daylight is longer than 11 hours, as is normal outside of the tropics. They are mostly propagated by stem or root cuttings or by adventitious roots called "slips" that grow out from the tuberous roots during storage. True seeds are used for breeding only.

They grow well in many farming conditions and have few natural enemies; pesticides are rarely needed. Sweet potatoes are grown on a variety of soils, but well-drained, light- and medium-textured soils with a pH range of 4.5-7.0 are more favourable for the plant. They can be grown in poor soils with little fertilizer. However, sweet potatoes are very sensitive to aluminum toxicity and will die about six weeks after planting if lime is not applied at planting in this type of soil. Because they are sown by vine cuttings rather than seeds, sweet potatoes are relatively easy to plant. Because the rapidly growing vines shade out weeds, little weeding is needed. In the tropics, the crop can be maintained in the ground and harvested as needed for market or home consumption. In temperate regions, sweet potatoes are most often grown on larger farms and are harvested before first frosts.

China is the largest grower of sweet potatoes, providing about 80% of the world's supply; 130 million tons were produced in 1990; about half that of common potatoes. Historically, most of China's sweet potatoes were grown for human consumption, but now most (60%) are grown to feed pigs. The rest are grown for human food and for other products. Some are grown for export, mainly to Japan. China grows over 100 varieties of sweet potato.

Sweet potatoes very early became popular in the islands of the Pacific Ocean, spreading from Polynesia to Japan and the Philippines. One reason is that they were a reliable crop in cases of crop failure of other staple foods because of typhoon flooding. They are featured in many favorite dishes in Japan, Taiwan, the Philippines, and other island nations. Indonesia, Vietnam, India, and some other Asian countries are also large sweet potato growers. Sweet potato, also known as kelang in Tulu is part of Udupi cusine. Uganda (the third largest grower after Indonesia), Rwanda, and some other African countries also grow a large crop which is an important part of their peoples' diets. North and South America, the original home of the sweet potato, together grow less than three percent of the world's supply. Europe has only a very small sweet potato production, mostly in Portugal. In the Caribbean, a variety of the sweet potato called the boniato is popular. The flesh of the boniato is cream-coloured, unlike the more popular orange hue seen in other varieties. Boniatos are not as sweet and moist as other sweet potatoes, but many people prefer their fluffier consistency and more delicate flavor.

Sweet potatoes have been an important part of the diet in the United States for most of its history, especially in the Southeast. From the middle of the 20th century, however, they have become less popular. The average per capita consumption of sweet potatoes in the United States is only about 1.5–2 kg (3.3–4.4 lb) per year, down from 13 kg (29 lb) in 1920. Southerner Kent Wrench writes: "The Sweet Potato became associated with hard times in the minds of our ancestors and when they became affluent enough to change their menu, the potato was served less often."

New Zealanders grow enough kūmara to provide each person with 7 kg (15 lb) per year, and they also import substantially more than this from China.

In the Southeastern U.S., sweet potatoes are traditionally cured to improve storage, flavor, and nutrition, and to allow wounds on the periderm of the harvested root to heal. Proper curing requires drying the freshly dug roots on the ground for two to three hours, then storage at 85–90 °F (29–32 °C) and 90 to 95% relative humidity from five to 14 days. Cured sweet potatoes can keep for thirteen months when kept at 55–59 °F (13–15 °C) and >90% relative humidity. Colder temperatures injure the roots.

Electronic sizing of sweet potatoes was first introduced to the industry by Wayne E. Bailey Produce Company of Chadbourn, North Carolina in 1990.

Diseases

Main article: List of sweet potato diseases

Nutrient content

Raw Sweet Potato

Nutritional value per 100 g (3.5 oz)
Energy	360 kJ (86 kcal)
Carbohydrates	20.1 g
Starch	12.7 g
Sugars	4.2 g
Dietary fibre	3.0 g
Fat	0.1 g
Protein	1.6 g
Vitamins and minerals Vitamins Quantity %DV† Vitamin A equiv. beta-Carotene lutein zeaxanthin 79% 709 μg 79% 8509 μg 0 μg Thiamine (B1) 8% 0.1 mg Riboflavin (B2) 8% 0.1 mg Niacin (B3) 4% 0.61 mg Pantothenic acid (B5) 16% 0.8 mg Vitamin B6 12% 0.2 mg Folate (B9) 3% 11 μg Vitamin C 3% 2.4 mg Vitamin E 2% 0.26 mg Minerals Quantity %DV† Calcium 2% 30.0 mg Iron 3% 0.6 mg Magnesium 6% 25.0 mg Phosphorus 4% 47.0 mg Potassium 11% 337 mg Sodium 2% 55 mg Zinc 3% 0.3 mg
†Percentages estimated using US recommendations for adults, except for potassium, which is estimated based on expert recommendation from the National Academies. Source: nutritiondata.com

Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta carotene (a vitamin A equivalent nutrient), vitamin C, and vitamin B₆. Pink, yellow and green varieties are high in carotene, the precursor of vitamin A.

In 1992, the Center for Science in the Public Interest compared the nutritional value of sweet potatoes to other vegetables. Considering fiber content, complex carbohydrates, protein, vitamins A and C, iron, and calcium, the sweet potato ranked highest in nutritional value. According to these criteria, sweet potatoes earned 184 points, 100 points over the next on the list, the common potato.

Sweet potato varieties with dark orange flesh have more beta carotene than those with light-colored flesh, and their increased cultivation is being encouraged in Africa, where vitamin A deficiency is a serious health problem. Despite the name "sweet", it may be a beneficial food for diabetics, as preliminary studies on animals have revealed it helps to stabilize blood sugar levels and to lower insulin resistance.

The peptic substance (0.78 percent total, 0.43 percent soluble) present in fresh tubers contains uronic acid (60%) and methoxyl (4-5%). Other constituents include phytin (1.05%), two monoaminophosphatides (probably lecithin and cephalin), organic acids (oxalic acid), phytosterolin, phytosterol, resins, tannins, and coloring matter.

Culinary uses

Japanese pastry

Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most important product. In some tropical areas, they are a staple food crop.

Africa

Amukeke (sun-dried slices of storage roots) and inginyo (sun-dried crushed storage roots) are a staple food for people in northeastern Uganda. Amukeke is mainly served for breakfast, eaten with peanut sauce. Inginyo is mixed with cassava flour and tamarind to make atapa. People eat atapa with smoked fish cooked in peanut sauce or with dried cowpea leaves cooked in peanut sauce.

The young leaves and vine tips of sweet potato leaves are widely consumed as a vegetable in West African countries (Guinea, Sierra Leone and Liberia, for example), as well as in northeastern Uganda, East Africa. According to FAO leaflet No. 13 - 1990, sweet potato leaves and shoots are a good source of vitamins A, C, and B₂ (riboflavin), and according to research done by A. Khachatryan, are an excellent source of lutein.

Asia

A Japanese yaki-imo vendor and cart outside Nara Park

In China, sweet potatoes, typically of the yellow variety, are baked in a large iron drum, and sold as street food during winter. In Japan, this is called yaki-imo (roasted sweeted potato), which typically uses either the yellow-fleshed Japanese sweet potato or the purple-fleshed (Okinawan) sweet potato.

Sweet potato soup, a Chinese tong sui (sweet soup) served during winter, consists of boiling sweet potato in water with rock sugar and ginger. Sweet potato greens are a common side dish in Taiwanese cuisine, often boiled or sautéed and served with a garlic and soy sauce mixture, or simply salted before serving. They, as well as dishes featuring the sweet potato root, are commonly found at bento (POJ: piān-tong) restaurants. In northeastern Chinese cuisine, sweet potatoes are often cut into chunks and fried, before being drenched into a pan of boiling syrup.

In Korean cuisine, sweet potato starch is used to produce dangmyeon (cellophane noodles). Sweet potatoes are also boiled, steamed, or roasted, and young stems are eaten as namul. Pizza restaurants such as Pizza Hut and Domino's in Korea are using sweet potatoes as a popular topping.

In Japan, boiled sweet potato is the most common way to eat it at home. Also, the use in vegetable tempura is common. Daigaku-imo is a baked sweet potato dessert. Because it is sweet and starchy, it is used in imo-kinton and some other wagashi (Japanese sweets), such as ofukuimo. Shōchū, a Japanese spirit normally made from the fermentation of rice, can also be made from sweet potato, in which case it is called imo-jōchū. Imo-gohan, sweet potato cooked with rice, is popular in Guangdong, Taiwan and Japan. It is also served in nimono or nitsuke, boiled and typically flavoured with soy sauce, mirin and dashi.

In Malaysia and Singapore, sweet potato is often cut into small cubes and cooked with yam and coconut milk (santan) to make a sweet dessert called bubur caca. A favourite way of cooking sweet potato is deep frying slices of sweet potato in batter, and served as a tea-time snack. In homes, sweet potatoes are usually boiled. The leaves of sweet potatoes are usually stir-fried with only garlic or with sambal belacan and dried shrimp by the Malaysian Chinese.

In some regions of India, fasts of religious nature are an occasion for a change in normal diet, and a total absence from cooking or eating is held as elective while a normal diet for a fasting day is a light feast consisting of different foods from usual, amongst which sweet potato is one of the prime sources of sustenance. Sweet potato is eaten otherwise, too, and a popular variety of preparation in most parts is roasted slow over kitchen coals at night and eaten with some dressing—primarily salt, possibly yogurt—while the easier way in the south is simply boiling or pressure-cooking before peeling, cubing and seasoning for a vegetable dish as part of the meal. Usually the preparations for sweet potato are similar to the blander ones for potato, while the sharper versions—with more green chili or red pepper—are reserved for potato.

In the Philippines, sweet potatoes (locally known as camote or kamote) are an important food crop in rural areas. They are often a staple among impoverished families in provinces, as they are easier to cultivate and cost less than rice. The tubers are boiled or baked in coals and may be dipped in sugar or syrup. Young leaves and shoots (locally known as talbos ng kamote or camote tops) are eaten fresh in salads with shrimp paste (bagoong alamang) or fish sauce. They can be cooked in vinegar and soy sauce and served with fried fish (a dish known as adobong talbos ng kamote), or with recipes such as sinigang. The stew obtained from boiling camote tops is purple-colored, and is often mixed with lemon as juice. Sweet potatoes are also sold as street food in suburban and rural areas. Fried sweet potatoes coated with caramelized sugar and served in skewers (camote cue) are popular afternoon snacks. Sweet potatoes are also used in a variant of halo-halo called ginatan, where they are cooked in coconut milk and sugar and mixed with a variety of rootcrops, sago, jackfruit and bilu-bilo (glutinous rice balls). Bread made from sweet potato flour are also gaining popularity. Sweet potato is relatively easy to propagate, and in rural areas that can be seen abundantly at canals and dikes. The uncultivated plant is usually fed to pigs.

In the mountainous regions of West Papua, sweet potatoes are the staple food among the natives there. Using the bakar batu way of cooking (free translation: burning rocks), rocks that have been burned in a nearby bonfire are thrown into a pit lined with leaves. Layers of sweet potatoes, an assortment of vegetables, and pork are piled on top of the rocks. The top of the pile then is insulated with more leaves, creating a pressure of heat and steam inside which cooks all food within the pile after a several hours. In most parts of Indonesia, sweet potatoes are frequently fried with batter and served as snacks.

North America

Sweet potato fries

Candied sweet potatoes are a side dish consisting mainly of sweet potatoes prepared with brown sugar, marshmallows, maple syrup, molasses, orange juice, marron glacé, or other sweet ingredients. Often served in America on Thanksgiving, this dish represents traditional American cooking and of that prepared with the indigenous peoples of the Americas when European American settlers first arrived. Sweet potato casserole is a side dish of mashed sweet potatoes in a casserole dish, topped with a brown sugar and pecan topping. Sweet potato pie is also a traditional favorite dish in Southern U.S. cuisine. Sweet potatoes slices are fried in bacon drippings and eaten with the bacon on toast. This is a traditional autumn breakfast food in rural Kentucky. Sweet potato fries or chips are another common preparation, and are made by julienning and deep frying sweet potatoes, in the fashion of French fried potatoes. Baked sweet potatoes are sometimes offered in restaurants as an alternative to baked potatoes. They are often topped with brown sugar and butter. Sweet potato butter can be cooked into a gourmet spread. Sweet potato mash is served as a side dish, often at Thanksgiving dinner or with barbecue.

New Zealand

Before European contact, the Māori used the small, yellow-skin, finger-sized kūmara known as taputini they had brought with them from east Polynesia. From about 1800, American whalers, sealers and trading vessels introduced larger varieties which quickly predominated. In New Zealand, Māori traditionally cooked the kūmara in a hāngi earth oven. This is still a common practice when there are large gatherings on marae. Now there are three main varieties of kūmara grown in the subtropical northern part of the North Island and widely available in New Zealand supermarkets, where they are a popular alternative to potatoes. Trials in New Zealand in 2000-2009 run by Fosse Leach, in the Cook Strait area, well south of the ideal warmer north, have shown that the taputini was capable of producing between 9.8 and 19.5 kg (depending on rainfall) per 5x5m plot in poor soil, with no fertilizer or modern methods. There were several other older Maori kumara varieties including Hutihuti and Rekamaroa.

Other

In the Solomon Islands, and neighboring Melanesian countries (as well as some parts of Polynesia), the sweet potato, along with the yam, also goes by the name common desert truffle. In Catalonia (northeastern Spain), sweet potato is called boniato. On the evening of All Souls' Day, it is traditional to serve roasted sweet potato and chestnuts, panellets and sweet wine. The occasion is called La Castanyada.

In Veneto (northeast Italy), sweet potato is known as patata mericana in the Venetian language (patata americana in Italian, meaning "American potato"), and it is cultivated above all in the southern area of the region; it is a traditional fall dish, boiled or roasted.

Nonculinary uses

Sweet potato, Moche culture, 300 AD, Larco Museum Collection

In South America, the juice of red sweet potatoes is combined with lime juice to make a dye for cloth. By varying the proportions of the juices, every shade from pink to black can be obtained.

All parts of the plant are used for animal fodder.

Sweet potatoes or camotes are often found in Moche ceramics.

Several selections are cultivated in gardens as ornamental plants for their attractive foliage, including the dark-leafed cultivars 'Blackie' and 'Ace of Spades' and the chartreuse-foliaged 'Margarita'. The species called wild sweet potato vine, man root, or man-of-the-earth, is not edible, but it is cultivated as an ornamental vine.

Researchers at North Carolina State University are breeding sweet potato varieties that would be grown primarily for biofuel production.

Names

Although it is sometimes called a yam, the sweet potato is not in the yam family, nor is it closely related to the common potato. The first Europeans to taste sweet potatoes were members of Columbus' expedition in 1492. Later explorers found many varieties under an assortment of local names, but the name which stayed was the indigenous Taino name of batata. This name was later transmuted to the similar name for a different vegetable, the ordinary potato, causing confusion from which it never recovered. The first record of the name "sweet potato" is found in the Oxford English Dictionary of 1775.

Kumara for sale, Thames, New Zealand.

Australia

95% of Australia's production is an orange variety named Beauregard sold everywhere as sweet potato. A purple variety, Northern Star, is 4% of production and is sold as Kumara. Occasionally shops will label the purple variety "purple sweet potato". There is also a white variety making up the last 1%.

Spain and Latin America

The Spanish took the Taino name batata directly, and also combined it with the Quechua word for potato, papa, to create the word patata for the common potato. In Mexico and Central America, the sweet potato is called by the Nahuatl-derived name camote. In Peru, the Quechua name for a type of sweet potato is kumar, strikingly similar to the Polynesian name kumara.

In South America, Peruvian sweet potato remnants dating as far back as 8000 BC have been found.

In Uruguay, the sweet potato is referred to as el boñiato.

For other languages' native words for sweet potato, see the Wiktionary entry for "sweet potato"

References

• Abidin, P.E. 2004. Sweetpotato breeding for northeastern Uganda: Farmer varieties, farmer-participatory selection, and stability of performance. PhD Thesis, Wageningen University, The Netherlands, 152 pp. ISBN 90-8504-033-7.
• Ahn, P.M., 1993, "Tropical soils and fertilizer use", Intermediate Trop. Agric. Series. Longman Sci. and Tech. Ltd. UK.
• Austin, D.F. 1988. The taxonomy, evolution and genetic diversity of sweetpotatoes and related wild species. In: P. Gregory (ed.). Exploration, maintenance, and utilization of sweetpotato genetic resources, pp. 27–60. CIP, Lima, Peru.
• Edmond, J. B., Ammerman, G. R. 1971. Sweet Potatoes: Production, Processing, Marketing. [Major Feed and Food Crops in Agriculture and Food Series.] Westport, Connecticut: The Avi Publishing Company.
• Hartemink, A.E., S. Poloma, M. Maino, K.S. Powell, J. Egenae & J. N. Sullivan, (2000). Yield decline of sweet potato in the humid lowlands of Papua New Guinea. Agriculture, Ecosystems and Environment 79 (2-3), 259-269.
• Purseglove, J.W. 1991. Tropical crops. Dicotyledons. Longman Scientific and Technical. John Wiley and Sons, Inc. NY. USA.
• Verrill, A.H., Foods America Gave the World, 1937, Boston: L.C. Page & Co.
• Woolfe, J.A., 1992, "Sweetpotato: an untapped food resource", Cambridge Univ. Press and the International Potato Center (CIP). Cambridge, UK.
• Zhang, D.P., M. Ghislain, Z. Huamán, J.C. Cervantes and E.E. Carey 1998. AFLP assessment of sweetpotato genetic diversity in four tropical American regions. CIP Program Report 1997-1998, pp. 303–310.

External links

• Sweet Potatoes
• BBC: "The mystery of the sweet potato"
• Consultative Group on International Agricultural Research
• Food and Agricultural Organization of the United Nations
• FAO Leaflet No. 13 - 1990 - Sweet Potato
• Japanese Society of Root and Tuber Crops
• World's Healthiest Foods: Benefits of Sweet Potatoes
• Sweet Potato Nutrition Information from USDA SR22 database