Zingiber officinale (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit; 2, leaf; 3, inflorescence; 4, flower

Zingiber officinale Roscoe

Protologue: Trans. Linn. Soc. London 8: 348 (1807).

Family: Zingiberaceae

Chromosome number: 2n = 22; tetraploids with 2n = 44 have been chemically induced

Synonyms

• Amomum zingiber L. (1753)

Vernacular names

• Ginger, common ginger (En)

• Gingembre (Fr)

• Indonesia: jahe, jae, lia

• Malaysia: haliya, jahi, atuja

• Papua New Guinea: kawawar, kawawari

• Philippines: luya (Tagalog), baseng (Ilocano), laya (Bicol)

• Burma (Myanmar): gyin

• Cambodia: khnhei, khnhei phlung

• Laos: khi:ng

• Thailand: khing, khing-daeng

• Vietnam: gừng, sinh khương

Origin and geographic distribution

Ginger has been grown in tropical Asia since ancient times. Wild forms of ginger have not been found and its origin is uncertain, although it is thought to come from India. It was brought to Europe and East Africa by Arab traders from India. Together with pepper, ginger was one of the most commonly traded spices during the 13th-14th Centuries. From East Africa, the Portuguese brought ginger to West Africa and other regions of the tropics during the 16th Century. At about the same period the Spanish introduced ginger into Jamaica, which still produces high quality ginger. At present, ginger is cultivated throughout the humid tropics.

Uses

Ginger is widely used as a spice, with its three main products being fresh ("green”) ginger, dried whole or powdered ginger, and preserved ginger. Fresh ginger is prepared from immature or mature rhizomes, the more pungent and aromatic dried ginger from mature rhizomes, and preserved ginger from immature rhizomes. The dried and preserved products are the major forms of internationally traded ginger, whereas fresh ginger is the major form of ginger consumed in the producing regions.

Fresh ginger is widely used in cooking in South-East Asia, as a flavouring or vegetable, and young rhizomes and stem parts are sometimes eaten raw, e.g. as "lalab”. Fresh ginger is also used to make ginger ale and other drinks. Ground dried ginger is applied worldwide for domestic culinary purposes, and also extensively in the flavouring of processed foods, especially in bakery products and desserts. Preserved ginger is used for domestic culinary purposes and in the production of processed foods such as jams, marmalades, cakes and confectioneries.

The fresh and dried rhizomes yield an essential oil ("ginger oil”) and oleoresin ("ginger extract”). Ginger oil has the aroma and flavour of the spice, but lacks pungency. It is used for flavouring beverages, in confectionery, and in cosmetics, perfumes and pharmaceuticals. Ginger oleoresin has the aroma, flavour and pungency of the spice itself. It is used for flavouring beverages and for similar purposes as the ground spice. It is seldom applied in cosmetics and perfumes because of its poor solubility in alcohol, but is used more often in pharmaceuticals. In the United States the regulatory status "generally recognized as safe” has been accorded to ginger (GRAS 2520), ginger oil (GRAS 2522) and ginger extract/oleoresin (GRAS 2521/2523).

Ginger has been used medicinally in Asia since ancient times, e.g. in China and India. It is still widely used in folk medicine, especially as a carminative, stimulant of the gastro-intestinal tract, rubefacient and counter-irritant. In Asia, the rhizome is also considered to have diaphoretic, diuretic, anti-inflammatory, anti-emetic and sialagogic properties, and it is used as an emmenagogue, abortifacient and vermifuge, whereas it also had a reputation as an aphrodisiac. Rhizome products are applied against a wide range of ailments, including nausea, diarrhoea, dysentery, dyspepsia, flatulence and other gastro-intestinal problems, fever, cough, colds, congestion of the chest, pleurisy, cramps and dropsy. Rhizome juice is used against migraine, catarrh, colic and to relieve menstrual cramps. Crushed rhizomes are applied externally against headache, toothache, rheumatism, intestinal problems, itch, boils and swellings. Various lotions, decoctions or poultices are rubbed on the body after childbirth, applied to swellings and bruises, used against rheumatism and to make baths against fever. In Malaysia, leaves are eaten against stomachache and rheumatism, pounded leaves are used externally for poulticing to treat headache, leaf juice is applied externally against ague in children, and young shoots may be used for lotions against rheumatism. In the Philippines, ginger tea is traditionally drunk to prevent hoarseness. Ginger is also applied as an antidote against snake poison in Indonesia, and fish and crab poison in China.

Ginger products, mainly the oleoresin, are official in several European pharmacopoeias and are used as ingredients in digestive, laxative, antitussive, carminative, antiacid and anti-emetic preparations.

Production and international trade

The bulk of the production of ginger is consumed locally in the producing countries, mainly as fresh ginger. In the 1980s, world production was estimated at about 100 000 t per year, of which about 25 000 t were exported, mainly by India (15 000 t). Other sources estimated annual world production of ginger in the early 1980s at 300 000 t, growing steadily to 500 000 t in 1990 and 600 000 t in 1998, with India, China, Indonesia and Nigeria being the main producers. In South-East Asia large amounts are also produced in the Philippines and Thailand. World production of ginger oil in the 1980s was estimated at 30 t annually, of which 20 t were exported, mainly by India (6-12 t) and China, the main markets being the United States, the European Union and Japan. The world production of ginger oleoresin was in the 1980s about 150 t annually, with the major producers being the United States, India and Singapore.

Properties

Dried ginger rhizomes contain per 100 g edible portion: water 10 g, protein 10-20 g, fat 10 g, carbohydrates 40-60 g, fibre 2-10 g and ash 6 g. A high fibre content is undesirable in rhizomes to be used as a spice.

The constituents responsible for the pungent taste are non-volatile phenols, the so-called gingerols, shogaols (dehydration products of gingerols), paradols and zingerone (a degradation product of gingerols), with [6]-gingerol being the most important. Freshly prepared dried rhizomes contain 1-2% gingerols.

The odour and much of the flavour is determined by the constituents of the pale yellow to orange-yellow essential oil, which has a rich, warm, spicy, somewhat lemony odour and a warm, spicy, aromatic taste. The essential-oil content of the rhizomes is usually 1-3% for the major types of commercial dried ginger. Though essential-oil yields above 3% are exceptional, yields up to 6% have been obtained from selected strains at experimental stations. The essential oil is a complex mixture of terpenes and non-terpenoid compounds. Compounds usually detected are α-zingiberene, β-zingiberene, ar-curcumene, β-sesquiphellandrene, α-farnesene and β-bisabolene (sesquiterpene hydrocarbons), and neral and geranial (oxygenated monoterpenes). On drying of the rhizomes, the monoterpene content of the oil decreases and the sesquiterpene content increases.

Ginger oleoresin contains pungent principles (gingerols and shogaols) as well as essential oil, together with fatty oil, fatty acids, resins and carbohydrates. It is a dark amber to dark brown viscous liquid, with an aromatic, warm, spicy, sweet odour, and a pungent, warm and biting taste. Extraction of the dried spice with organic solvents yields 3.5-10% oleoresin, containing 15-30% volatile compounds.

The types of ginger entering the world market are identified by their origin of production. Each type possesses a characteristic aroma and flavour mainly influenced by cultivar, ecological conditions and the production and post-harvest practices employed. Major ginger types come from Jamaica, Nigeria, Sierra Leone, India, Australia and China. Jamaican ginger is highly reputed because of its good appearance and delicate aroma and flavour. Cochin ginger from southern India is of comparable quality. Nigerian ginger has a coarser flavour and aroma, with pronounced camphoraceous notes; its high oil content and strong pungency makes it in demand for oil distillation and oleoresin extraction, as is the case with Sierra Leone ginger. Indian ginger has a lemon-like flavour and aroma, is more starchy, rather pungent, and sought after by ginger beer manufacturers. Chinese ginger has been the standard for ginger preserved in syrup. Most gingers are suitable for oleoresin production, but Jamaican ginger oleoresin is preferred by soft-drink manufacturers and African ginger oleoresin by the meat industry.

With regard to the medicinal properties, ginger exhibits antispasmodic and anti-inflammatory activity, helps reduce cholesterol, lower blood pressure and shrink liver tumour in test animals. In humans rhizome powder is effective against nausea, e.g. post-operative nausea, motion sickness and morning sickness. The principles responsible for this anti-emetic activity might be [6]-, [8]- and [10]-shogaols and [6]-, [8]- and [10]-gingerols. Ethanolic rhizome extracts have shown inhibition of skin tumour promotion in mice. Zingiberene, β-sesquiphellandrene, ar-curcumene and [6]-shogaol show anti-ulcer principles. Furthermore, [6]-gingerol has been shown to be a cholagogue after intraperitoneal administration in rats, and [8]-gingerol to have hepatoprotective activity, as it prevents the toxic effects of carbon tetrachloride in rat hepatocytes.

Ginger oil has considerable antifungal and antibacterial activity, and is used as a seed dressing in India. Meat cooked with fresh rhizomes becomes more tender due to the action of the proteolytic enzyme zingibain.

A monograph on the physiological properties of ginger oil has been published by the Research Institute for Fragrance Materials (RIFM) and by the European Scientific Cooperative on Phytotherapy (ESCOM).

Composition

Ginger oil (from India) (Source: Lawrence, 1988.)

• 30.0% zingiberene
• 9.0% β-sesquiphellandrene
• 8.0% camphene
• 8.0% ar-curcumene
• 7.0% cis-γ-bisabolene
• 6.0% β-bisabolene
• 4.2% β-phellandrene
• 3.1% limonene
• 2.5% α-pinene
• 2.0% citronellol
• 1.4% α-terpinyl acetate
• 1.0% 1,8-cineole
• 0.9% myrcene
• 0.9% geranial
• 0.8% nerolidol (unknown isomer)
• 0.6% linalool
• 0.6% β-eudesmol
• 0.5% neral
• 0.5% germacrene D
• 0.5% germacrene B
• 0.4% β-pinene
• 0.4% citronellal
• 0.4% citronellyl acetate
• 0.4% zingiberenol
• 0.4% trans-β-sesquiphellandrol
• 0.3% α-phellandrene
• 0.3% cis-sesquisabinene hydrate
• 0.2% elemol
• 0.2% phellandral
• 0.2% 6-methyl-5-hepten-2-one
• 0.2% rosefuran
• 0.1% α-thujene
• 0.1% sabinene
• 0.1% para-cymene
• 0.1% γ-terpinene
• 0.1% borneol
• 0.1% α-terpineol
• 0.1% β-caryophyllene
• 0.1% fenchyl acetate
• 0.1% cis-sabinene hydrate
• 0.1% perillene
• 0.1% isoborneol
• 0.1% α-eudesmol
• 0.1% 2-hexanone
• 0.1% (--)-isopulegol
• 0.1% 2-nonanone
• 0.1% 2-heptanone
• 0.1% cubebol
• 0.1% carvotanacetone
• 0.1% δ-3-carene
• 0.1% α-terpinene
• 0.1% (Z)-β-ocimene
• 0.1% (E)-β-ocimene
• 0.1% terpinolene
• 93.0% total

Ginger oil (from China) (Source: Vernin & Parkanyi, 1994.)

• 38.1% zingiberene
• 17.1% ar-curcumene
• 7.2% β-sesquiphellandrene
• 5.2% β-bisabolene
• 4.7% camphene
• 2.5% β-phellandrene
• 2.2% borneol
• 2.1% 1,8-cineole
• 1.3% α-pinene
• 1.2% β-elemene
• 1.0% limonene
• 0.8% α-terpineol
• 0.7% geraniol
• 0.6% myrcene
• 0.5% β-caryophyllene
• 0.4% nerolidol (unknown isomer)
• 0.4% 6-methyl-5-hepten-2-one
• 0.3% zingiberenol
• 0.2% cis-sesquisabinene hydrate
• 0.2% β-pinene
• 0.2% terpinolene
• 0.2% α-phellandrene
• 0.1% trans-β-sesquiphellandrol
• 0.1% 2-undecanone
• 0.1% sabinene
• 0.1% para-cymene
• trace 2-heptanol
• trace 2-nonanone
• trace α-copaene
• 87.0% total

Ginger oil (from Malaysia) (Source: Ibrahim, H. & Zakaria, M.B., 1987.)

• 65.0% sesquiterpene hydrocarbons
• 5.1% bornyl acetate
• 4.6% camphene
• 2.7% limonene
• 2.5% linalyl acetate
• 2.2% α-pinene
• 2.0% 1,8-cineole
• 1.2% β-bisabolene
• 1.1% linalool
• 1.0% ar-curcumene
• 0.4% β-copaene
• 0.4% β-pinene
• 0.4% camphor
• 0.4% α-humulene
• 0.3% terpinen-4-ol
• 0.3% β-farnesene
• 0.2% neral
• 0.2% β-caryophyllene
• 0.2% β-elemene
• 0.2% α-guaiene
• 0.2% para-cymene
• 90.8% total

Adulterations and substitutes

Several Zingiber species produce a spice or an essential oil used as adulterants of or substitutes for Z. officinale, e.g. Z. spectabile Griffith, Z. montanum (Koenig) Dietrich, Z. mioga (Thunb.) Roscoe and Z. zerumbet (L.) J.E. Smith.

Ginger oil is sometimes adulterated with monoterpene hydrocarbons.

Description

• Erect, slender, perennial herb usually grown as an annual, with a thickened, fleshy, subterranean rhizome and with one or more aerial leafy stems, up to 1.25 m tall. Rhizome robust, fleshy, up to 2 cm thick, growing horizontally underground but at shallow depth, irregularly branched but normally only in the vertical plane, covered with deciduous, thin scales which leave ring-like scars; epidermis corky, pale yellow to reddish, irregularly wrinkled in the dried rhizome; flesh pale yellow, aromatic; on dried rhizomes scars of leafy stems visible as shallow cup-like holes. Stem erect, unbranched, mainly formed by the leaf sheaths, pale green, often reddish at base; scales covering the lower part oblong, about 6 cm × 1 cm, scarcely white-pilose outside, with prominent parallel veins and scarious margins.
• Leaves distichous; sheath prominently veined, densely appressed pilose, especially so in the upper part, with white, scarious, glabrous margins; ligule up to 5 mm long, bilobed, glabrous to sparsely pilose, scarious; blade linear to lanceolate, up to 30 cm × 2 cm, acuminate at apex, finely parallel-veined, glabrous above, scarcely pilose below, light to dark green.
• Inflorescence arises direct from rhizome, spiciform, 15-30 cm long; scape slender, 10-20 cm long, below the spike covered with scales as on the leafy stem bases, the upper ones sometimes with short leafy tips; spike ovoid to narrow ellipsoidal, 4-7 cm × 1.5-2.5 cm, light green; bracts appressed, ovate to elliptical, 2-3 cm × 1.5-2 cm, yellow-green, margin scarious, incurved, the lower ones with slender whitish acute tips, glabrous, finely parallel-lined; in the axil of each bract one flower may be produced.
• Flowers fragile, short-lived, surrounded by a spatha-like bracteole; bracteole narrower and slightly longer than the bract, usually persisting and enclosing the fruit; calyx tubular-spathaceous, 10-12 mm long, whitish; corolla tubular, pale yellow, widening at top into 3 lobes, tube 18-25 mm long, dorsal lobe long ovate, 15-25 mm × 7-8 mm, with beak-like rounded apex curved over the anther, ventral lobes oblong, 13-15 mm × 2-3 mm, apex rounded, 3-veined, strongly recurved; labellum about circular in outline, 12-15 mm in diameter, tubular at base (tube 3-4 mm), 3-lobed above; central lobe obovate, 12 mm × 9 mm, side lobes elliptical, 5 mm × 3.5 mm; labellum pale yellow outside, inside dark purple or red at top and at margins, mixed with yellowish spots, scattered pilose at throat; filament about 1.5 mm long, anther 2-celled, ellipsoidal, 7-9 mm × 3 mm, pale yellow, connectivum prolonged into a slender, curved, purple, beak-like appendage 7 mm long, enclosing the upper part of the style; ovary globose, 2 mm in diameter, 3-locular; style filiform, 3.5 cm long, white, slightly recurved and widening at top, ending in a funnel-shaped white stigma which is ringed with stiff hairs around its upper margin; 2-3 fleshy, sublinear, white nectaries, 5 mm long, are situated against the style on top of the ovary.
• Fruit a thin-walled capsule, 3-valved, red. Seed small, arillate, black.

Growth and development

The first shoots of ginger appear 10-15 days after planting the rhizomes, and new shoots appear continuously until about 4 weeks after planting. Each shoot has about 8-12 leaves.

Flowering is cultivar-dependent. Some cultivars flower rarely, others regularly, especially when grown undisturbed as perennials. In Malaysia ginger flowers only rarely. Ginger fruits are seldom produced.

Ginger rhizomes normally only branch in the vertical plane, so they are flat on the sides and stand upright in the soil. They have a main axis, with at least one side axis to the left and the right, with these side axes again forming 2 side axes, etc. Only some of the side axes develop aboveground shoots.

Other botanical information

Various ginger types have been characterized in Malaysia, e.g. the "haliya betai”, the true ginger possessing pale-coloured rhizomes and the "haliya bara” and "haliya indang” with very pungent reddish rhizomes used primarily in medicine. Taxonomically, the two main groups can be named: Z. officinale cv. group Officinale, which is cultivated throughout the tropics, and Z. officinale cv. group Rubrum ("haliya padi”), grown on a small scale in South-East Asia for medicinal use and as a spice. The latter differs from the former by having smaller, red-coloured rhizomes with a stronger and more pungent odour, the red colouring of the basal parts of leafy stems and petioles, larger leaves, and by the presence of a larger, scarlet-red mottled labellum. In Indonesia, three types of ginger have been distinguished: (1) "jahe gajah”, "jahe badak” or "jahe putih besar”; (2) "jahe merah” or "jahe sunti”; (3) "jahe putih kecil” or "jahe emprit”. Their rhizomes differ in shape, colour, aroma and chemical composition, and all types can be considered as cultivars.

Ecology

Ginger is grown in the tropics from sea-level up to 1500 m altitude, but is mostly found at low altitudes. The crop prefers warm, sunny conditions, and though it may benefit from shade during hot periods, especially when young, shading is generally considered unnecessary. The optimum rainfall is 2500-3000 mm, well-distributed over the year. Below 2000 mm, supplementary irrigation is necessary, but ginger seldom succeeds as an irrigated crop in dry areas, because the required humidity cannot be maintained profitably. Ginger is very sensitive to waterlogging.

The preferred soils are medium loams with an adequate supply of organic matter, but ginger is grown on a wide range of soils with a pH of 6.0-7.0. As it is an exhaustive crop, the soil fertility must be high or manure should be applied.

Propagation and planting

Ginger is propagated vegetatively by pieces of rhizome called seed pieces or sets. They are normally produced by cutting rhizomes into 3-6 cm long pieces of 30-60 g, with at least one growing point or bud. Medium to large-sized seed pieces produce more vigorous plantlets and higher yields than small ones. To prevent diseases, seed pieces may be dipped in a fungicide solution and air-dried prior to planting. Seed pieces can be pre-germinated to obtain uniform plants, reduce the number of missing hills in the field and allow for once-over harvesting. Pre-germination may be promoted by placing the sets 2.5 cm apart on raised beds, covered with compost, sawdust or manure or both and kept moist. The sets are ready for transplanting after 3-5 weeks or when the sprouts are 1-2 cm long.

In vitro micropropagation of ginger from shoot tips, meristems or rhizome sections is possible. A suitable growth medium for shoot multiplication is a modified Murashige-Skoog medium, supplemented with 2-3 mg/l of 6-benzylaminopurine. Through in vitro propagation, it is possible to obtain large quantities of disease- and pest-free planting material, but little is known about the performance of micropropagated ginger in the field. Micropropagated plants in an Indian study needed 10 months to reach the same yield and oleoresin levels as conventionally propagated ginger after 8 months. Under field conditions in Queensland, growth and yield of micropropagated plants of the first generation ex vitro were inferior to those of plants derived from seedpieces, but by the second generation, the differences had disappeared. Micropropagation is already used in the Australian ginger industry for rapid multiplication of promising new cultivars, which are then propagated by more conventional methods.

Before planting ginger, the field should be thoroughly prepared to a fine tilth, free of weeds, roots and residues of previous crops. Normally, ginger is planted in rows, with 25-30(-50) cm between rows and 15-35 cm within the row. In the Philippines, the recommended planting distance is 50-70 cm between rows and 30 cm within the row. The normal planting depth is 5-12 cm, with one seedpiece per hole. In the fully mechanized estates in Queensland, 8-10 t of sets are needed to plant 1 ha: under less intensive conditions in India and Sri Lanka 1.5-4 t/ha are needed.

At planting time the soil must be moist and not dry out once the sets are planted. The preferred soil temperature at planting is 25°C and should not exceed 30°C. Planting in the Philippines takes place in May. Recommended planting time is March-April in India, and September in Queensland.

It is recommended to practise rotation and to grow ginger only once in 3-4 years, to reduce the incidence of pests and soilborne diseases. Ginger is often found in intercropping systems. It is often the first crop on land taken into cultivation.

In vitro production of active compounds

The essential oil in ginger rhizomes of plantlets, produced in vitro from shoot-tips on different growth media, has been reported to contain the same constituents as the oil of the original rhizome, but the quantities of these constituents varied with basal medium composition and the amount of growth regulators added.

Husbandry

For optimal yields and high quality production it is essential to weed ginger. Manual weeding is common, and any rhizomes that have become exposed are covered at the same time. Manual and mechanical weeding should be shallow, to avoid damaging to the rhizomes.

Mulching may be practised to conserve soil moisture and reduce soil temperature. Materials used for mulching include coconut fronds, sawdust, rice husks or straw, sugar cane trash and sheet polythene.

Normally, 100 kg/ha of N is required, of which at least one third should be applied at planting, and the remainder in 1-3 top dressings. Phosphate should generally be applied in similar amounts as nitrogen, preferably at planting. Potassium is normally applied at planting, but can also be given in several applications. Fertilizers are sometimes applied in the form of specifically manufactured "ginger mixtures” (e.g. 8-8-16 in India, 13-13-21 in Fiji and 12-14-10 in Australia). In the Philippines 50 t fresh rhizomes removed about 247 kg N, 71 kg P₂O₅ and 100 kg K₂O per ha from a loamy soil. It was therefore recommended that for soils of low fertility 250 kg N, 100 kg P2O5 and 100 kg K₂O per ha should be applied at 4 different times during the growing season: 100 kg N and the total amount of P and K just before or at planting, and the remaining N in equal side dressings at 60, 90 and 120 days after planting.

Diseases and pests

In general, diseases are more damaging in ginger than pests, so disease prevention or control is an essential component of commercial ginger growing. The most important diseases are rhizome rots, often caused by Pythium spp., Fusarium spp. and Rosellinia spp. The main symptom is degeneration of rhizomes into a black, putrefying mass, whereas aboveground the leaf tips, sheaths, margins, and gradually whole leaves turn yellow, followed by desiccation and death. Another widespread and serious disease is bacterial wilt, caused by Pseudomonas solanacearum, which occurs for instance in Indonesia, Malaysia, the Philippines and Thailand. The symptoms include progressive yellowing and wilting from the lower leaves to the whole plant, with badly affected stems and rhizomes yielding a milky exudate when cut. Leaf spots caused by Colletotrichum spp., Helminthosporum spp., Cercospora spp. and Septoria spp. are also common.

Most insect pests are only of local importance. However, foliage pests may become damaging in a specific location or season. The most important foliage pest in Asia, especially India, is the shoot borer Dichocrocis punctiferalis. In the Philippines the shoot borer Ostrinia furnacalis is an important insect pest. Ginger is also attacked by nematodes (Meloidogyne spp.), inducing the formation of galls or swellings on the roots. Severe infestations may lead to the death of the crop.

Control measures for the above diseases and pests include choosing a well-drained site for ginger cultivation, practising crop rotation and selecting healthy rhizomes and treating them with fungicides before planting.

Harvesting

Timing of harvesting of ginger rhizomes depends on their intended use, as the relative content (on a dry weight basis) of essential oil, pungent constituents and fibre increases with age of the crop. The content of essential oil and the pungent principles of the rhizomes reaches a maximum about 9 months after planting, decreasing later on, whereas the fibre content continues to increase. When intended for consumption as a fresh vegetable (green ginger), rhizomes may be harvested about 5 months after planting. For the production of preserved ginger, they are usually harvested 5-7 months after planting, before they are fully mature and while still tender, succulent and mild in pungency, and with low fibre content. For dried ginger, mature rhizomes that have developed a full aroma, flavour and pungency are used. These are harvested 8-9 months after planting, when leaves begin to yellow and stems start to lodge. Harvesting is accomplished either by hand with a spade, hoe or digging fork, or by mechanical diggers. Harvesting should be done very carefully, to minimize damage to the rhizomes.

Yield

Generally, it can be assumed that ginger rhizomes lose about 75-80% of their weight during drying. Yields of dried rhizomes from smallholdings are usually below 3 t/ha, compared with 10-15 t/ha obtained on commercial farms in Australia. In Africa and the Caribbean, yields are seldom higher than 2 t/ha. In the Philippines, the average commercial yield of fresh ginger is 6-7 t/ha.

Handling after harvest

To prepare dried ginger, fresh rhizomes are washed and soil particles, roots and shoots are removed. Rhizomes are then killed by immersion in boiling water for ten minutes, or by peeling, scraping or slicing, and then dried. Rhizomes with the peel either carefully scraped off ("uncoated” or "white” ginger) or retained ("coated” or "black” ginger) are usually sun-dried for several days to yield the dried ginger of commerce. Uncoated ginger is sometimes treated with lime to improve its white colour and reduce insect attack. Dried rhizomes can be pulverized to produce ground ginger. In Australia, mechanical washing and drying are practised.

Ginger oil and oleoresin can be obtained from fresh or dried rhizomes. Ginger oil is obtained by steam distillation, oleoresin by extraction with organic solvents such as acetone, alcohol or ether. Both coated and uncoated ginger can be used for oil distillation and oleoresin extraction, but coated rhizomes are preferred. Oil yields from coated rhizomes are higher than from uncoated ones, as the epidermal tissue is rich in oil-containing cells. The presence of pungent compounds responsible for the taste of ginger oil can be substantially reduced by poor post-harvest handling or improper distillation.

Ginger rhizomes are often heavily contaminated with microorganisms that can be treated with ethylene oxide or gamma irradiation to avoid health problems. In most importing countries, dried ginger has to meet strict quality and cleanliness criteria, commonly based on the American Spice Trade Association (ASTA) specifications.

Rhizomes to be used as planting material can be stored in many ways. A simple method is to leave a part of the field unharvested, cut the foliage, cover the field with mulch and dig up the rhizomes when needed. Other methods are pit storage, used e.g. in India, where mature rhizomes are treated with a fungicide, shade-dried and placed in pits, which are then covered, and storage in smoke houses. Cold storage is not recommended, because rhizome viability is gradually reduced and may become zero after short periods below 0°C.

Genetic resources

There are many locally important ginger cultivars. More than 400 ginger accessions are maintained at the Indian Institute for Spices Research in Calicut, Kerala, India, and new collections are added from time to time. In Indonesia, 45 ginger accessions collected from all over the country are being maintained at the Research Institute for Spices and Medicinal Crops in Bogor.

Breeding

Breeding of ginger has been severely hampered by poor flowering and seed set. Moreover, cultivars are rather uniform because of vegetative propagation. Hence most of the crop improvement programmes are confined to the evaluation and selection of the naturally occurring clonal variation and the introduction of cultivars from abroad. In India, work is also being done on in vitro selection for resistance to rhizome rot and bacterial wilt.

Prospects

Ginger is a popular spice, and its consumption will probably increase. However, further increases in yield and production are hampered by the major diseases (rhizome rot and bacterial wilt) for which more effective control measures need to be developed. Improving seed set is important to facilitate breeding work. Locally, as in the Philippines, the current high price of fresh ginger on the local market may provide an incentive for farmers to venture into ginger production. However, it is often difficult to obtain large quantities of planting material, and to overcome disease and post-harvest problems.

Literature

• Aycardo, H.B., 1979. Production for fresh market and processing. In: Bautista, O.K. & Aycardo, H.B. (Editors): Ginger: production, handling, processing, marketing. Department of Horticulture, College of Agriculture, University of the Philippines at Los Baños, the Philippines. pp. 1-23.

• Lawrence, B.M., 1997. Progress in essential oils. Perfumer and Flavorist 22(5): 71-83.

• Dake, G.N., 1995. Diseases of ginger (Zingiber officinale Rosc.) and their management. Journal of Spices and Aromatic Crops 4: 40-48.

• Leung, A.Y. & Foster, S., 1996. Encyclopedia of common natural ingredients used in food, drugs and cosmetics. 2nd edition. John Wiley & Sons, New York, United States. pp. 271-274.

• Nayar, N.M. & Ravindran, P.N., 1995. Herb spices. In: Smartt, J. & Simmonds, N.W. (Editors): Evolution of crop plants. 2nd edition. Longman Scientific and Technical, Harlow, United Kingdom. pp. 491-494.

• Perry, L.M., 1980. Medicinal plants of East and Southeast Asia. Attributed properties and uses. The MIT Press, Cambridge, Massachusetts, United States. p. 443.

• Sakamura, F. & Suga, 1989. Zingiber officinale Roscoe (ginger): in vitro propagation and the production of volatile constituents. In: Bajaj, Y.P.S. (Editor): Biotechnology in agriculture and forestry. Vol. 7. Medicinal and aromatic plants 2. Springer Verlag, Berlin, Germany. pp. 524-538.

• Smith, M.K. & Hamill, S.D., 1996. Field evaluation of micropropagated and conventionally propagated ginger in subtropical Queensland. Australian Journal of Experimental Agriculture 36: 347-354.

• Theilade, I., 1996. Revision of the genus Zingiber in Peninsular Malaysia. The Gardens' Bulletin Singapore: 48(1-2): 207-236.

• Weiss, E.A., 1997. Essential oil crops. CAB International, Wallingford, Oxon, United Kingdom. pp. 539-567.

Sources of illustrations

Purseglove, J.W., Brown, E.G., Green, C.L. & Robbins, S.R.J., 1981. Spices. Vol. 2. Longman, Harlow, Essex, United Kingdom. Fig. 8.1, p. 451. Redrawn and adapted by P. Verheij-Hayes.

Authors

• H. Sutarno, E.A. Hadad & M. Brink