Geography and distribution
The exact origin of Curcuma longa is not known, but it is thought to originate from South or Southeast Asia, most probably from Vietnam, China or western India.
It is only known as a domesticated plant and not found in the wild.
India is the world’s largest producer, consumer and exporter of turmeric. Turmeric is also cultivated extensively in Bangladesh, China, Thailand, Cambodia, Malaysia, Indonesia and the Philippines.
Pressed and dried specimen of Curcuma longa from Kew’s Herbarium.
Overview: An upright, perennial herb to about 1 m tall. The rhizome (underground stem) is thick and ringed with the bases of old leaves. Turmeric only reproduces via its rhizomes.
Leaves: Large, oblong, up to 1 m long, dark green on upper surface, pale green beneath. Each leafy shoot (pseudostem) bearing 8–12 leaves.
Flowers: Yellow-white, borne on a spike-like stalk 10–15 cm long. Flowers are sterile and do not produce viable seed.
Seeds: Small, ovoid, brown. Not viable.
History of turmeric
Turmeric has been used in India for at least 2,500 years. It was recorded in China by 700 AD, East Africa by 800 AD and West Africa by 1200. It was introduced to Jamaica in the 18th century. Today, turmeric is widely cultivated throughout the tropics.
Turmeric was probably cultivated at first as a dye and then became valued as a condiment as well as for cosmetic purposes. In the 13th century Marco Polo wrote of this spice, marvelling at a vegetable that exhibited qualities so similar to saffron.
Familiar to the contemporary world as a prime component of curry powder, the orange-yellow rhizome's striking colour lent it a special aura in ancient India. It has always been considered an auspicious material in the subcontinent, both amongst the Aryan cultures (mostly northern) and the Dravidian cultures (mostly southern), and its value may extend far in history to the beliefs of ancient indigenous peoples. Turmeric's common name in the north, haldi, derives from the Sanskrit haridra, and in the south it is called manjal, a word that is frequently used in ancient Tamil literature.
Turmeric has a long history of medicinal use in South Asia, cited in Sanskrit medical treatises and widely used in Ayurvedic and Unani systems. Susruta's Ayurvedic compendium, dating to 250 BC, recommends an ointment containing turmeric to relieve the effects of poisoned food.
Powdered rhizomes of turmeric, from West Bengal in 1886 (EBC 40530).
Turmeric rhizomes are used as a bright yellow-orange culinary spice. Turmeric has been known as poor man's saffron because it offers a less expensive alternative yellow colouring, but the flavour it gives to food is different from true saffron, which comes from a species of Crocus (Iridaceae).
The rhizomes can be cured for use as a spice by boiling and steaming. They can also be boiled in water, dried, peeled and then ground. Turmeric is an important yellow food dye and is added to many Indian dishes including curries. It is also added to pickles and can be used instead of saffron to add colour and flavour to rice.
Turmeric is a main ingredient of curry powder. The rhizomes are cooked, dried and then ground to produce the strongly coloured, aromatic powder.
Ground rhizomes are used to make turmeric oil that is used in the industrial production of flavouring for curries. Turmeric was often hung in kitchens as a good luck charm, and a small rhizome was sometimes tied to the pots in the kitchen for luck.
In Europe and the USA, turmeric is widely used as a colouring agent in processed foods, sauces, pharmaceuticals, confectionery and textile dyes.
Turmeric rhizomes yield a bright yellow dye that is used as a colouring for foods, textiles, paints and even people! Its primary use is in crafts as a fabric dye.
To prepare the yellow dye, the dried or fresh rhizomes are ground to a paste with water. The resulting dye has always been popular during the Hindu festival Holi, which people celebrate by covering themselves with bright dyes. Now synthetic dyes tend to be used instead, but these can be harmful to the skin. Making natural dyes from plants like turmeric may be safer, although this cannot always be assumed to be true.
Few people still use traditional dyeing techniques in South Asia, but turmeric dye gives a yellow colouring to silk, cotton and wool. The yarn or fabric is dipped into the liquid, or the dye can be painted directly onto fabric.
Another ingredient called alum might also be added. Alum works as a mordant to help the dye bond with the fabric. Even with the use of alum, turmeric dye tends to fade over time. Various shades of yellow can be made, depending upon which other ingredients are used and how much turmeric is added.
The colour of turmeric can vary depending on whether the liquid it is mixed with is alkali or acid. In an alkali solution, it will turn red, but if acid is added to neutralise the alkali then the colour will change to yellow. This can be seen in traditional dyeing techniques where acid might be added at various stages. For one technique in Calcutta, turmeric and Fuller's earth (a clay that removes impurities) was used. This makes an alkali solution, so acidic lime juice was added to neutralise it. Other acids that were used include sour milk, dried mango in water or tamarind water.
Turmeric is also mixed with other dyes to make different colours. Traditionally when dyeing silk yarn, the yarn would first be dyed with turmeric to give a richer colour. Orange colours can be made in different ways using yellow turmeric paste, red pigment from safflowers (Carthamus tinctorius) and acidic mango rind in water. To make green, cloth can be dyed yellow with turmeric and then blue with indigo (Indigofera tinctoria) or vice versa.
Turmeric is also used to make a yellow paint for various folk painting traditions in Madhya Pradesh.
Turmeric has been used for many conditions in traditional medicine in India, Pakistan and Bangladesh. The rhizome is the part that is most widely used. It can be prepared in various ways and is reputed to alleviate asthma and coughs. Many of its traditional uses are supported by scientific evidence.
Hot water extracts of the dried rhizome have been taken orally in Ayurvedic medicine to reduce inflammation. Turmeric is also regarded as a 'rasayana' herb, which is a branch of Ayurvedic medicine and is used to counteract ageing processes.
In Unani medicine, turmeric has been used for conditions such as liver obstruction and jaundice and has been applied externally for ulcers and inflammation. Roasted turmeric has been used as an ingredient of a preparation used to treat dysentery. Turmeric has also been used in tooth powder or paste.
A hot water extract of the dried rhizome taken orally was reputed to slow lactation, regulate fat metabolism, help symptoms of diabetes, diarrhoea and liver diseases, and as a tonic calm the stomach. The fresh juice taken regularly on an empty stomach has been used to prevent stomach disorders. A hot water extract of the dried rhizome was reputed to have an abortion-promoting effect when taken orally or in the form of a pessary (when inserted into the vagina).
Externally, the dried rhizome has been applied to fresh wounds and insect stings and to help the healing process in chickenpox and smallpox. Turmeric was reputed to improve complexion of the skin and has been applied externally to remove hair, act as a tonic and alleviate itching. Inhalation of turmeric smoke is reputed to relieve hiccups.
Turmeric rhizomes have also been mixed with other plants to produce traditional remedies for a range of conditions including tonsillitis, headaches, wounds, snake bites, stings, sprains and fractured bones.
Turmeric is not widely used in Western medicine, but has been investigated as a treatment for some conditions. Studies show that the rhizomes contain compounds that may have therapeutic effects, which appear to support some of its uses in traditional medicine.
Turmeric has been shown to have anti-bacterial, anti-fungal, antioxidant and anti-inflammatory effects, to which can be added possible anti-ulcer, wound-healing, liver-protective and anti-cancer properties.
It contains yellow pigments called curcuminoids. One example of a curcuminoid is curcumin. Turmeric and curcumin are being investigated for any beneficial effects they might have on conditions such as cancer, dementia and irritable bowel syndrome and for potential cholesterol-lowering effects.
Some studies suggest that components of the essential oil, such as ar-tumerone, have anti-snake venom activity. The essential oil is also reported to have some insect repellent and insecticidal activity.
Cultural/ spiritual uses
Yellow and yellow-orange are colours that have sacred and auspicious connotations on the Indian subcontinent. Turmeric is important in Hindu and Buddhist ceremonies.
Turmeric is associated with fertility and prosperity and considered to bring good luck if applied to a bride's face and body, as part of the ritual purification before a wedding. Turmeric roots may be given as a present on special occasions, such as a visit to a pregnant woman. Turmeric powder is also sprinkled on sacred images. The use of turmeric is prohibited in a house of mourning.
Yellow and orange are both special colours in Hinduism, yellow being associated with Vishnu, and as the colour of the space between chastity and sensuality. Orange signifies sacrifice, renunciation and courage. Originally associated with the sun as part of solar symbolism, the colours were absorbed into the mythology of Hinduism.
Chakras in Hindu belief are mystical centres of orientation. Orange represents the sacral chakra, and yellow represents the solar plexus chakra. This yogic concept is of the inner cosmology of a being discovered through meditative practice. It is best described in the tantras or texts important in Tantric Hinduism and Vajrayana Buddhism. In Buddhism yellow is the colour of the Bodhisattva Ratnasambhava.
Extracts have been added to creams as a colouring agent, and traditionally women would rub turmeric into their cheeks to produce a golden glow. One of the main yellow pigments in turmeric is curcumin (described above under Western medicine).
In Hindu wedding ceremonies, brides would rub turmeric over their bodies. Newborn babies had turmeric rubbed on their forehead for good luck, and they would be given a turmeric necklace to wear to keep away evil spirits.
In India pieces of the rhizomes are added to water to make an infusion used in baths. It is reported that washing in turmeric improves skin tone and reduces hair growth.
An unusual use for turmeric is in the chemistry laboratory. Turmeric goes dark red in the presence of alkaline (basic) substances, such as baking powder. Strips of paper soaked in turmeric can therefore be used as an indicator.
Turmeric is used in the laboratory alongside litmus paper, which turns blue in the presence of bases and red in the presence of acids.
Production & trade
Illustration of Curcuma longa by Franz Eugen Kohler, from Kohler's Medicinal Plants, 1887.
Key producers of turmeric include India, Pakistan and Bangladesh. India is the biggest producer, supplying some 20,000 t each year (94% of the world's demand). It enters the international market in the form of dried whole rhizomes or as ground rhizomes. The major importers are Iran, Sri Lanka and Middle Eastern and North African countries.
Turmeric is cultivated commercially as an annual crop, by planting small rhizomes or pieces of rhizome on flat soil or in furrows between ridges. The growing plants require heavy application of manure to get the best yield.
Turmeric is ready for harvesting 7 to 10 months after planting, when the lower leaves turn yellow. Harvesting is carried out by digging up the rhizomes. Leafy tops are then cut off and the roots and adhering earth are removed. Rhizomes are then washed. Some of these are retained for replanting as a future crop. The remainder are processed into turmeric.
To develop the yellow colour and characteristic aroma, cleaned rhizomes are cooked in boiling water for an hour under slightly alkaline conditions. The cooked rhizomes are then dried, either artificially or in the sun, for 6 to 8 days. Dried rhizomes are polished to smooth their exterior and to improve the colour. They are sold in this form or ground into a powder.
Adulteration and substitutes
In India, the deliberate contamination and bulking out of turmeric is a serious problem in local markets. On an international scale, the problem may not be so serious, but closely related species are frequently substituted for true turmeric. Fortunately, chemical analysis can to some extent establish how pure a product is.
Ground turmeric is the most vulnerable product, particularly in local markets. Here, it is not uncommon to find turmeric powder adulterated with lead chromate, yellow earth, sand or even cheap talc.
In the international market, concern over possible adulteration is associated mainly with the mixing of related Curcuma species containing similar pigments. Species that have been used as a substitute include C. xanthorrhiza, C. aromatica and C. zedoaria.
In Asian producing countries, these three species are used as a source of starch and dyes and in folk medicine as a substitute for true turmeric. It is often difficult to identify these species by microscopic examination of the powder. However, adulteration of true turmeric by C. aromatica and C. zedoaria can be detected by chemical methods.
Turmeric is a low-growing tropical herbaceous plant, which forms many long thin rhizomes. Turmeric can only be grown indoors in temperate regions and is a little tricky to at first, but once the dormancy of the rhizome has been broken it is easy to grow as a houseplant. Plants grown this way will not yield much useful turmeric, although the leaves can be used for flavouring.
Perennial. Only suitable for growing indoors or in a heated greenhouse in temperate regions. Minimum temperature 18°C.
Fresh, plump, juicy looking rhizomes should be selected from raw turmeric sold for food. Rhizomes with a little tooth-like bud on one side should be chosen. They should be laid tooth side up in a seed tray containing a mixture of seed compost and grit, just covering the rhizomes. The tray should be placed in a clear plastic bag, and the bag sealed and kept warm, preferably with bottom heat, at 20°C, for at least three weeks. When shoots emerge, the bag should be removed and the tray kept damp in a warm light place but not in direct sunlight.
The rhizomes should be potted on as soon as the shoots are 5 cm high, into shallow 15 cm pots. They should be kept damp and warm, in a slightly shaded position and fed weekly during the growing season with general-purpose liquid fertiliser. In dry weather plants will benefit from being lightly misted daily with rainwater.
During autumn, watering should be reduced, and plants should be kept fairly dry over winter, when they will need more light. Draughty locations should be avoided.
Red spider mite can be an occasional problem in older plants: regular misting and keeping leaves well-washed will reduce this.
Asian and Caribbean shops often sell fresh turmeric, although the quality is variable: sometimes if it has been airfreighted in cold temperatures the rhizomes fail to develop shoots, or they may have been treated by dormancy-inducing chemicals.
Turmeric plants are available from a number of nurseries.
If the roots are cut the yellow colour will stain fingers or cloth indelibly, and contact may cause an allergic skin reaction in some people.
This species at Kew
Curcuma longa rhizomes in Kew’s Economic Botany Collection (EBC 37181).
Curcuma longa can be seen growing in Kew’s Palm House.
Dried and spirit-preserved specimens of Curcuma longa are held in Kew’s Herbarium, where they are available to researchers by appointment.
Specimens of Curcuma longa, including leaves, wood, fruit slices, rhizomes, powder and oil, are held in Kew’s Economic Botany Collection.