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Cyperus esculentus (or chufa sedge, nut grass, yellow nutsedge, tigernut sedge, or earth almond) is a crop of the family sedge native to warm temperate to subtropical regions of the Northern Hemisphere. It can be found wild, as a weed or as a crop. It has been cultivated since the fourth millenium bc in Egypt, and for several centuries in Southern Europe. Nowadays it is often cultivated for its edible tubers (tigernuts), mainly in Spain for the preparation of the milky beverage Horchata de chufa. But in many countries C. esculentus is considered a weed and it is underutilized.

Taxonomy
There are several varieties: The most important cultivated species is Cyperus esculentus var. sativus Boeckl, also called Chufa.
 * Cyperus esculentus var. esculentus - Mediterranean region east to India
 * Cyperus esculentus var. hermannii - Florida
 * Cyperus esculentus var. leptostachyus - United States
 * Cyperus esculentus var. macrostachyus - United States
 * Cyperus esculentus var. sativus - Asia, cultivated origin

History
Zohary and Hopf consider this tuber "ranks among the oldest cultivated plants in Ancient Egypt." Although noting, "Chufa was no doubt an important food element in ancient Egypt during dynastic times, its cultivation in ancient times seems to have remained (totally or almost totally) an Egyptian specialty." Its dry tubers have been found in tombs from predynastic times about 6000 years ago. In those times, C. esculentus tubers were consumed either boiled in beer, roasted or as sweets made of ground tubers with honey. The tubers were also used medicinally, taken orally, as an ointment, or as an enema, and used in fumigants to sweeten the smell of homes or clothing. There are almost no contemporary records of this plant in other parts of the old World. Presently, they are cultivated mainly, at least for extended and common commercial purposes, in Spain, where they were introduced by Arabs, almost exclusively in the Valencia region. They are found extensively in California and were grown by the Paiute in Owens Valley.

Tigernut is also cultivated in countries like Chile, Brasil, USA,Ghana, Nigeria, Burkina Faso, Northern Cameroon and Mali, where they are used primarily as animal feed or uncooked as a side dish.

Biology
It is an annual or perennial plant, growing to 90 cm tall, with solitary stems growing from a tuber. The plant is reproduced by seeds, creeping rhizomes and tubers. The stems are triangular in section and bear slender leaves 3–10 mm wide. The spikelets of the plant are distinctive, with a cluster of flat, oval seeds surrounded by four hanging, leaf-like bracts positioned 90 degrees from each other. They are 5 to 30 mm long and linear to narrowly elliptic with pointed tips and 8 to 35 florets. The colour varies between straw – colored to gold – brown. They can produce up to 2420 seeds per plant. The plant foliage is very tough and fibrous and is often mistaken for a grass. The roots are an extensive and complex system of fine, fibrous roots and scaly rhizomes with small hard, spherical tubers and basal bulbs attached. The tubers are between 0.3 – 1.9 cm in diameter and the colours varies between yellow, brown and black. One plant can produce several hundred to several thousand tubers during a single growing season. With cool temperatures foliage, roots, rhizomes and basal bulbs die. But the tubers survive and resprout the following spring when soil temperatures remain above 6°C. They can resprout up to several years later. When the tubers germinate, many rhizomes are initiated and end in a basal bulb near the soil surface. These basal bulbs initiate the stems and leaves above ground, and fibrous roots underground. C. esculentus is wind pollinated and requires cross pollination as it is self–incompatible.

Climate requirements
For the tigernut cultivation, amild climate is needed. Tigernut cultivation needs a mild climate. Low temperature, shadow and light intensity can inhibit flowering. Tuber initiation is inhibited by high levels of nitrogen, long photoperiods and high levels of gibberellic acid. Flower initiation occurs under photoperiods of 12 – 14 hours per day.

Soil requirements
Tubers can develop in soil depths of around 30 cm, but most occur in the top or upper part. They tolerate many soil conditions including periods of drought and flooding and survive soil temperatures around -5°C. They grow best on sandy, moist soils which contents and a pH between 5.0 – 7.5. They do not tolerate salinity.

Cultivation Management
Planting is normally done on flat soils where ridges to favour the coming irrigations have previously been done. The separation between ridges is approximately 60 cm and seeds are planted manually. Distances between seeds may vary from 15 to 20 cm and seeding depth is around 8 cm. The normal ratio of tigernuts used as seeds for planting is around 200/300 Kg tubers/ha. They are planted between april and may and must have to be irrigated every week until they are harvested in november and december. Tubers develop about 6 – 8 weeks after seedling emergence and grow quickly during july and august. The maturing is around 90 - 110 days. The average yield can approach between 10 and 19 t/ha. Weeds need to be removed weekly during the growing stage, as they could cause a reduction on tigernut size. The fields must have to be fertilized before planting by using natural fertilizers such as manure or compost. Thus the soil will recuperate its nutrients.

Harvest and Drying process
Harvest usually occurs in november or december and the leaves are scorched during the harvest. With a combine harvester, the tigernut is pulled out of the ground. Immediately after harvesting, the tigernuts are washed with water in order to remove sand and small stones. The drying occurs usually in the sun and can take up to three months. The temperatures and humidity levels have to be monitored very carefully during this period. The tigernuts have to be turned every day to ensure uniform drying. The drying process ensures a longer shelf - live. This prevents rot or other bacterial infections, securing quality and high nutrition levels. Disadvantages in the drying process are shrinkage, skin wrinkler and hard nut texture by dehydration.

Storage
Tigernut loses a considerable amount of water during drying and storage. The starch content of the tigernut tubers decreases and the reducing sugar (invert sugar) content increases during storage. Tigernut can be stored dry and rehydrated by soaking without losing the crisp texture. Soaking is usually an overnight operation and is important in the process for some foods such as legumes, grains and some vegetables. Since it reduces the time necessary to reach the required texture during cooking. A common characteristic of dried tigernut is a hard texture and low moisture content. Therefore, soaking is indispensable to render them edible with ease and to ensure acceptable sensory quality.

Nutritional value
Despite its name, tigernut is a tuber. However, its chemical composition shares characteristics with tubers and with nuts. It has been reported to be a “health” food, since its consumption can help prevent heart disease and thrombosis and is said to activate blood circulation and reduce the risk of colon cancer. This tuber is rich in energy content (starch, fat, sugar, and protein), minerals (mainly phosphorus and potassium), and vitamins E and C thus making this tuber also suitable for diabetics. Tigernut tubers contain almost twice the quantity of starch as potato or sweet potato tubers. The oil of the tuber was found to contain 18% saturated (palmitic acid and stearic acid) and 82% unsaturated (oleic acid and linoleic acid) fatty acids. The moderately high content of phytosterols further enriches the quality and value of tigernut oil as a food source.

According to the Consejo Regulador de Chufa de Valencia (Regulating Council for Valencia's Tigernuts), the nutritional composition/100 ml of the famous milky spanish beverage horchata de chufas is as follows: energy content around 66 kcal, proteins around 0.5 g, carbohydrates over 10 g with starch at least 1.9 g, fats at least 2 g.

Uses
Dried tigernut has a smooth tender, sweet and nutty taste. It can be consumed raw, roasted, dried, baked or as tigernut milk or oil.

Use as food
The tubers are edible, with a slightly sweet, nutty flavour, compared to the more bitter-tasting tuber of the related Cyperus rotundus (purple nutsedge). They are quite hard and are generally soaked in water before they can be eaten, thus making them much softer and giving them a better texture.

They have various uses; in particular, they are used in Spain to make horchata. “Horchata” is a nonalcoholic beverage of milky appearance derived from the tubers of the tigernut plant mixed with sugar and water. It has a great economic impact in the Valencian region of Spain. Flour of roasted tigernut is sometimes added to biscuits and other bakery products as well as in making oil, soap, and starch extracts. It is also used for the production of honey, nougat, jam, beer, and as a flavoring agent in ice cream and in the preparation of kunnu (a local beverage in Nigeria). Kunnu is a nonalcoholic beverage prepared mainly from cereals (such as millet or sorghum) by heating and mixing with spices (dandelion, alligator pepper, ginger, licorice) and sugar. To make up for the poor nutritional value of kunnu prepared from cereals, tigernut was found to be a good substitute for cereal grains. Tigernuts oil can be used naturally with salads or for deep frying. It is considered as high quality oil. Tigernut “milk” has been tried as an alternative source of milk in fermented products, such as yogurt production, and other fermented products common in some African countries and can thus be useful replacing milk in the diet of people intolerant to lactose to a certain extent.

Use as oil
There is a global search for alternative sources of fuel which could be cheaper, safer and more importantly, environmentally friendly in comparision with widely used burning fuels. Since the tubers of C. esulentus contain 20-36% oil, it has been suggested as potential oil crop for the production of biodiesel.

Use in medicine and cosmetic industry
As a source of oils, the tubers were used in pharmacy under the Latin name bulbuli thrasi beginning no later than the end of 18th century. In ayurvedic medicine tigernuts are used in the treatment of flatulence, diarrhoea, dysentery, debility and indigestion. Tigernut oil can be used in the cosmetic industry. As it is antidioxide (because of its high content in vitamin E) it helps slow down the ageing of the body cells. It favours the elasticity of the skin and reduces skin wrinkles.

Use as fishing bait
The boiled nuts are used in the UK as a bait for carp, and have a reputation for success. The nuts have to be prepared in a prescribed manner to prevent harm to the fish. The nuts are soaked in water for 24 hours and then boiled for 20 minutes or longer until fully expanded. Some anglers then leave the boiled nuts to ferment for 24–48 hours, which can enhance their effectiveness. If the nuts are not properly prepared, however, they can be extremely toxic to the carp. This was originally thought to have been the cause of death of Benson, a very large and very famous carp. The 54-lb. fish was found floating dead in a fishing lake, with a bag of unprepared tigernuts lying nearby, empty, on the shore. An examination of the fish by a taxidermist concluded tigernut poisoning was not, in the end, the cause of death.

Appearance as an invasive weed
C.esculentus is known as one of the world’s worst weeds. It is a weed for over 21 crops in more than 30 countries around the world. The plant is extremely difficult to remove completely from lawns and gardens, where it is considered an intrusive weed. This is due to the plant having a stratified and layered root system, with tubers and roots being interconnected to a depth of 36 cm or more. The tubers are connected by fragile roots that are prone to snapping when pulled, making the root system difficult to remove intact. Intermediate rhizomes can potentially reach a length of 60 cm. The plant can quickly regenerate if a single tuber is left in place. In its competition for light, water and nutrients it can reduce crop yields and compromise quality. It can develop into a dense colony of around 3 diameters. Patch boundaries can increase by more than one meter per year. Tubers and seed disperse with agricultural activities, soil movement or by water and wind. They are often known as a contaminant in crop seeds. When plants are small they are hard to distinguish from other weeds such as Dactylis glomerata and Elytrigia repens. Thus it is hard to discover in an early stage and therefore hard to counteract. Once it is detected, many options for combating this weed, such as mechanical, by hand, grazing, damping and herbicides were used. Up to now, nobody found the ultimate solution.

Similar native or non-native species that can confuse identification

 * Sedges (Cyperus) have grass-like leaves and resemble each other in the appearance. They can mainly be distinguished from grasses by their triangular stems.


 * Purple nutsedge (C. rotundus) is another weedy sedge that is similar to the yellow nutsedge (C. esculentus). These two sedges are difficult to distinguish from each other and can be found growing on the same site. Some differences are the purple spikelets and the tubers formed by C.rotondus are often multiple instead of just one at the tip. In addition the tubers have a bitter taste instead of the mild almond - like flavour of C.esculentus.