Green Gold of The East: A light Review of Cloves
There has not been any definite date on when actually human first consumes cloves but for the record, the history of cloves usage can be traced back as far as 220 – 206 BC. In Han period, the great Emperor of China recommended every court official to chew on cloves before consulting with or addressing the Emperor to make sure that his breath was clean (http://drclarkia.com/cloves.asp). Cloves were imported into Alexandria as early as 176. By the 4th century they were well known in the Mediterranean and by the 8th century they were sold so expensively in Europe (Purseglove, 1968). Traditional herbal books claimed that a man could regain potency by drinking sweet milk that was garnished with three grams of crushed cloves (Swahn, 1991).
In 335, Constantine the Great sent 45 kilograms of cloves to Saint Sylvester I, neatly packed in jars. One could only speculate on the meaning of the gift as “odor of holiness” and few centuries after wards, clove became a blessing of medicine.
During the ninth century at the wealthy monastery of Sankt Gallen in Switzerland, monks sprinkled cloves on their fasting – fish. In 973, an Arab traveler, Ibn Jaqub found the burghers of Mainz seasoning their meals with cloves. Saint Hildegard discussed cloves in her book about medicinal plants during the twelfth century.
By then, clove had long been a source of joy to spice traders ranging from Italians in Genoa and Venice to their Arab suppliers in Alexandria and the Levant and beyond. The tree of cloves would be planted in some part of the world for trading and exchange commodities.
riginally, clove trees are native to spice islands of “Molucca” as such Ternate, Tidore, Mutir, Makyan, and Bachian, where wild clove trees can be found. In fact, Francisco Serrao reached the Moluccas in 1511 and settled in the clove island of Ternate. More expeditions to the island were established after wards. The Portuguese were quick to out - compete the Arab spice merchants and establish their own monopoly using fortified trading posts, treaties with island rulers and naval bases. Their policy was simple: all spice should be sent to Lisbon in Portuguese ship and sold from there at solid profit. They screwed up the prices and executed any foreigners who traded with clove and nutmeg in Moluccas (Swahn, 1991).
However, in the late sixteenth century Portugal was conquered by Spain and Dutch drove out Portuguese from Moluccas and then a new imperialism based on cloves was started in the Island. Cornelius van Houten returned in 1597 to Amsterdam with huge cargo of spices and more than twenty ships full of cloves arrived in the following year. The new empire did not bring any better social welfare for the natives when dealing with demand of cloves worldwide. In fact, the Dutch only allowed certain areas for growing the clove trees while plantation sites cultivating clove trees but considered difficult to control were burnt down. At least 60,000 natives were killed during acquisition of clove plantation in Molucca (Swahn, 1991).
Despite of the imposed restriction by Dutch, Piere Poivre managed to smuggle sixty clove plants with fast sail through the isle of Jibby of the Moluccas in 1773 to Mauritius. Two of the stolen trees bore fruit in 1775. Plants were taken to Cayenne about 1789 from whence they were introduced into Dominica, Matinique and other West Indian islands. Smith sent a total 55,265 plants to Penang in 1802 through By the East India Company and in the 1820’s extensive clove plantations were made in Penang, Singapore and Malacca but they were not successful. British introduced the clove plants to some extent in Sri Lanka, India, and Tahiti after wards (Kochar, S. L., 1981). At the same token Sultan Said bin Sultan forced plantation owners to plant cloves under threat of confiscation of their land and more of the area of Zanzibar and Pemba was planted with cloves by 1820’s (Purseglove, 1968).
Vernacular names: clou de girofle (Fr), cengkeh (Ind.), klabong pako (The Phil.), lay-hnyin (Bur.), khan phluu (Camb.), dinh huwowng (Viet.), do:k chan (Laos), kruidnagel (Dutch), nelke (German), lavang (Gujarati), ding xiang (Chinese), etc.
Synonym of Syzygium aromaticum (L.) Merrill & Perry is Caryophyllus aromaticus L., Eugenia caryophyllata Thunb, Eugenia aromatica O.K., Jambosa caryophyllus NDZ; 2n=22.
Clove belongs to the family Myrtaceae. Myrtaceae comprise 129 genera with about 4600 species worldwide, most of them shrubs with simple and leathery leaves. There are a number of economically important Myrtaceae due to their abundant secretary cavities or oil glands that contain essential oils with strong fragrances, which can be used in several ways. A well-known example is pimentum (Pimenta dioica). The family is said to be taxonomically complicated.
There has been a controversy over taxonomy of Syzygium aromaticum between the old world and the new worlds. Clove was originally named Caryophyllus aromaticus by Linnaeus but later transferred to the genus Eugenia L. by Thunberg. Today most taxonomists agree that the species is better placed in Syzygium Gaertner. A number of characters in flower and fruit distinguish the exclusively old-World genus Syzygium from Eugenia, which mainly encompasses new world taxa. .
Close relatives of the Clove are Syzygium polyanthum (Wight) Walpers, widely distributed in South-east Asia and also a source of spice, as well as Syzygium cumini (L.) Sheels, S. Jambos (L.) Alston and S. Malaccense (L.) Merr. & Perry. Their fruits are also edible.
Cloves tree thrives best with insular maritime climates in the tropics at low altitudes. Continuously humid climates are not so suitable. In the original habitat in Moluccas, where the trees are semi-wild, annual rainfall is 218 – 355 cm and temperatures 24 – 33C. Drier weather is desirable for harvesting and drying the crop. The best solids for cloves are deep, sandy, red and acid-loams. Good deep drainage is essential and water logging is fatal (Murty, and Subrahmanyam, 1989).
The tree is slender and can reach up to 15 m tall, conical when young, later becoming cylindrical, in cultivation usually smaller and branched from the base. Roots form an extensive dense mat close to the surface. The primary tap - root usually remains short but it produces 2 – 3 primary sinkers which reach a depth of about 3 m. Horizontal lateral roots grow to a length of about 10 m and produce a surface plate of feeding roots and occasionally send out secondary sinkers to the lower levels. The bark is grayish smooth and the wood of stem is hard but brittle (Purseglove, 1968). The leaves are shiny dark green (sometimes reddish), opposite and decussate persistent, minutely puntated, elliptical in shape, 6 – 13 cm x 3 – 6 cm and aromatic (De Guzman and Simonsma, 1999).
eedlings are raised immediately after harvesting because the seed may lose its viability within few weeks. Hulled washed seeds produce better seedlings than un-hulled seeds. Propagation is usually carried out in shaded nurseries and then transplanted into the field (Kochar, 1981). Due to low merismetic activity, clove plants are notoriously difficult to propagate vegetatively (Purseglove, 1968). The young plants grow slowly and juvenile phase lasts about 4 years. Clove yields increase until the tree is about 20 years and it will be productive until 80 years. The crop cycle starts with a major flush as soon as the rainy season has settled in. Minor flushes of leafy shoots occur at irregular intervals but bearing trees stop flushing before harvest and resumes after harvest. Flushing is usually encouraged by the loss of branches due to harvesting but root pruning and growth retardants can suppress it. The shoot-growth pattern in the course of the years governs flowering. Flowers are hermaphrodite and usually cross-pollinated by bees.
he inflorescences emerge from the green terminal buds a few weeks after the leaves of the flush have turned green. The inflorescences expand in a series of well-defined stages. First a trident is formed. Thereafter, the inflorescence branches further, largely in multiple of three until the proliferation of the inflorescence is complete. The extent of branching varies and strongly affects the size of the crop. In the penultimate stages, each flower primordium assumes the typical clove shape. Reversal of floral primordial into leaf primordial some times occurs during the early stages. It takes 6 – 8 months before the flower buds are ready for harvest. The crop is harvested when the flower buds are fully-grown and green or beginning to turn red but before they open (Cobley and Steele, 1976). If the tree is not harvested the fruit matures three months later (De Guzman and Simonsma, 1999).
Macroscopical and Microscopical Characters of Cloves.
Figure 1. Clove bud
he name “clove” ultimately derives from Latin “clavus”, which means nail because of shape resemblances. The word made its way to English via Old French “clou”. Cloves are 10 – 17 mm long (Fig. 1). The stalk of the clove consists of a cylindrical hypanthium or swelling of the tours above which is a bi-locular ovary containing numerous ovules attached to placentae. The head consists of four slightly projecting calyx teeth; four membranous imbricated petals and numerous incurved stamens surrounding a large style (Fig. 2. E). Cloves have a strong fragrant and spicy odor and a pungent, aromatic taste. When indented with fingernail, they readily exude oil (Trease and Evans, 1983).
Figure 2. A, Penang clove; B, Zanzibar Clove; C, fruit; D,stalk, E, clove cut longitudinally; F, transverse section of Hyphantium; G, portion of anthers; H, Surface view petals; a, stamens; ae, aerenchyma; al, anthers love; c, columnella; cr, cluster crystal of calcium oxalate; e, epidermis; h, hyphanthium; o, ovules; og, oil gland; p, imbricated
he hypanthium in the region below ovary shows in transverse section a heavy cuticularized epidermis (Fig. 2F) in which occur stomata, slightly raised above the surface and showing well-defined sub-stomata spaces. Within this is a zone of roughly and radially arranged parenchymatous cells containing schizolysigenous oil glands arranged in two or three more or less intermixed layers. The oil glands are ellipsoidal in shape, with the long axis radial and show an epithelium composed or two or three layers of flattened cells. The contents of the oil glands are soluble in alcohol and are blackened by treatment with alcoholic ferric chloride. Cluster crystals of calcium oxalate occur in many parenchymatous cells. The sepals and petals show simplified leaf structure. The mesophyll parenchyma contains calcium oxalate and embeds numerous oil glands. The epidermis of petals is devoid of stomata and is composed of very irregular cells. The stamens are composed of filament, connective and anthers. The fibrous layer of the anther wall is composed of cells showing spiral bands of lignified thickening (Trease and Evans, 1983).
Clove contains a volatile oil, 14 to 20%; gallotannic acid, 10 to 30%; oleanolic acid, vannilin, eugenin and other extraneous materials associated with dried plant products (Robbers et al., 1996).
Most of the volatile oil of the cloves is in the form of eugenol (4-allyl-2-methoxyphenol). Eugenol is prepared from clove oil by shaking with 10% solution of sodium hydroxide to form sodium eugenolate. The mixture was washed with ether, and the sodium eugenolate is then decomposed with sulfuric acid. The eugenol is separated by steam distillation. It is a colorless or pale yellow, thin liquid that has a strongly aromatic odor of clove and a pungent spicy taste. Further eugenol can be converted into vanillin for other flavorings.
In practice, leaves, stems and buds can be used as source of volatile oil. Nevertheless, buds contain the highest percentage followed by stems and leaves. Boiling the benzene-insoluble extract of clove buds results in caryophyllene (Rogers, 1966).
Most essential oils are obtained from the plant materials by a process of known as steam distillation. Essential oils contain substances with boiling points up to 200C or higher. In the presence of steam or boiling water, however, these substances are volatilized at a temperature close to 100C at atmospheric pressure. The mixture of hot vapors will if allowed to pass through a cooling system, condense to form a liquid in which the oil and water comprise two distinct layers. Most (but not all) essentials oils are lighter than water Ames and Mathews, 1968).
Cloves Usages: Before, Current and Future
Clove is considered to be the most fragrant of all aromatic spices. Gustatory and sensory experts have described it to be “exquisitely scented, exhaling perfume rare and delicious”. The aroma of ground cloves has been characterized as being spicy, peppery, sweet, fruity, phenolic, woody and musty. The flavor has similarly characterized as warm, spicy, fruity, astringent, slightly bitter with a warm numbing effect (Farell, 1990).
Curry powder, which is an essential spice for Indian diets, is mixed ingredients containing clove. Curry will be tasted differently without clove. In Asia, it is still a practice to chew betel quid as stimulant. The betel quid is made of chopped areca nut mixed with lime, folded in a leaf of betel pepper and flavored and fastened with clove. People in the west usually use cloves for mixing ingredients, tomato and other sauces, for seasoning sausages, apple pudding and tarts, for decorating and improving flavor of hams, four sousing herrings and other fish and being stuck in oranges to make pomanders (Purseglove, 1968). Some other typical uses are baked apple dishes, pastry spice, cakes, cookies, fruit soups, pickles, preserves, spicy sweet syrups, sausages, hamburger, pork shoulder roast, stews, sweet rolls and spicy vegetables (Farell, 1990).
Kretek cigarettes are composed of one third of shredded cloves and two thirds of shredded tobacco leaves. The cigarettes were identified as “kretek cigarettes” because they are giving out cracking sounds when being smoked. Nevertheless, the cigarettes become strong, pungent and aromatic. These cigarettes are favored in Asian societies that are the biggest market of the cigarettes.
Moreover, steam distilled of clove oil has also been used in cosmetics, bathing soaps, and detergents. As a flavor, clove oils have been used to make semi synthetic vanillin that is the widest applied flavor at the moment.
Although mainly known as a spice for flavoring dishes and bakery nowadays, clove was mainly used as a medicine where it was indigenous. Rumphius in the 18th century was probably the first to describe clove and its usages from the island of Ambon. He mentioned it to be used for smoking and medical purposes, e.g. for stomach disorders. In a much later account on clove from South-East Asia the following actions have been attributed to the flower-bud and the fruit by local healers: carminative, vermifuge, emmenagogue, tonic, stomachic, anti-emetic, anti-nauseant, febrifuge and, when applied locally, analgesic and anti-rheumatic. Moreover, sore throat, whooping cough, morning sickness and muscular cramps can be cured by consuming cloves in different form (http://www.emrc.org/clove.html).
It has been reported that Chinese were only allowed to approach the emperor with some clove-buds in the mouth in order to mask halitosis due to teeth decay. Traditional Chinese physicians have used clove to treat indigestion, diarrhea, intestinal worm infection as well as painful bruises. The same was true for the traditional Indian, the Ayurvedic medicine.
When clove became better known in Europe around the 4th century A.D., it also attracted the attention of medieval healers, who used it in several ways, e.g. to treat gouty conditions. Whereas for a long period of time the buds or fruits were used entirely or fragmented, American physicians were the first to use extracted clove oil from the buds in their medications.
A number of more than 30 constituents of clove oil have in the meantime been characterized, but the following three account for most of it: Eugenol (80-95%), eugenyl acetate (1-5%) and beta caryophyllene (4-12%).
The effects of these compounds have been increasingly investigated in recent years in order to understand the effects of traditional medicines and to find newer perspectives of treatment.
Clove was considered to be panacea for mouth and tooth-problems. It still has some role in dental medicine and oral hygiene. Some of the beneficial effects in acute inflammation seem to be due to the high anesthetic capacity of beta-caryophyllene. On the other hand there is clear evidence that many ingredients of clove exhibite antibacterial activity against important oral pathogens (Cai and Wu, 1996) and may therefore be an important prophylactic. A fascinating new medical aspect is the inhibitory effect of Acetyl- eugenyl on platelet aggregation.(Srivastava, 1991). Platelet aggregation and clot-formation are a serious problem in atherosclerotic heart vessels and cause hearth infection. So far this information comes only from in vitro research.
Hot water extract of Syzygium aromaticum when administered to in vitro showed anti-cytomegalovirus (CMV) activity. When orally administered to mice the activity of cytomegalovirus was also suppressed in the lungs (Yukawa et al., 1996).
Another area of ongoing studies is concerned with the anti-viral properties of clove extracts, against Herpes. Administration of combined both acyclovir and extract of S. aromaticum showed strong combined therapeutic anti-HSV-1 activity in mice and especially reduction of virus yield in the brain (Kurokawa, et al., 1995).
In terms of anti-fungal activity, growth of three toxigenic strains of Aspergilli cultured on ground clove (1.5 g) and sterile water for 30 days was completely inhibited. Ground clove (0.1% w/v) in rice powder and corn steep liquor medium completely inhibited mycelium growth and afla-toxin production of A. flavus after an incubation periods of six days. 200 – 250 ppm of eugenol in potato dextrose agar inhibited the growth and toxin production of Aspergilus parasiticus (http://www.fao.org/docrep/x2230e/x2230e15.htm).
Toxicity of Clove Oil
It is important also to notice that although clove oils have been claimed to bring medicinal benefits, lay people are advised not to consume clove oils blindly for any purposes. Administration of both clove oils and eugenol orally has an LD50 of 3720 and 500 mg, respectively (http://www.fao.org/docrep/x2230e/x2230e15.htm). Therefore, the administration should be limited.
Production and International Trade
Generally for Asia, Pemba and Zanzibar, cloves are considered very important for the economy of the countries. Clove consumption varies from country to country and hence so is the demand. An average Indonesian burns up to about 151 grams of clove per year; an Italian needs only one gram annually to season pasta; Other westerners including American, however, consume about 7 – 9 grams per year for marinades, beverages and so on. According to the global spice market, the worldwide demand for cloves were only 2% of the total and was still far behind capsicum and pepper which were accounted for 25% and 17%, respectively (www.intracen.org/mds/sectors/spices/rep1.pdf). The main reason for this is that clove is a very strong spice and hence only little is needed for consumption to have sufficient effect.
Moreover, in order to have a commercial value, cloves have to meet an international quality standard as it can be seen in the table 1. The Moisture, ash and extraneous content should not be higher than specified in table 1, while the volatile oil should be at least the same as or higher than specified on table.
Table 1. Specification of Marketable Clove products
Extraneous Matter (%w/w)
Moisture Content (%w/w)
Total Ash (% dry basis)
Volatile oil (%, ml/100g; dry basis)
Source: De Guzman and Simonsma, 1999.
The unit price for imported clove has been steady if not increased since 1994. From 1994 to 1998, the average unit price was 0.964 US $/Kg. European Union, USA and Japan have remained the largest importer of cloves while Indonesia, India, China, Malaysia and Brazil are top 5 of clove suppliers in a decreasing order (www.intracen.org/mds/sectors/spices/rep1.pdf). The UNTAC/WTO reported that clove production in Madagascar, Zanzibar and Pemba has been declining due to climate instability.
Threats to the Clove Plantation
Apart from reaching a bearing age and being replaced by the new types of economical valuable plants, clove tree is also under threat for survival from pathogens.
In India it was reported that clove tree was infected by Corynespora. The pathogen was responsible for the development of a leaf spot disease. Infection started on the lamina as minute, oval to sub-circular, reddish brown spots. Gradually the spots increased in size, became irregular in shape and reached a diameter up to 3 cm. Later, the center turned dull-white and was surrounded by a reddish brown margin. The central core of the lesion became thin, papery and necrotic on which clumps of conidiophores bearing conidia appeared as minute black spot (Saiki and Sarbhoy, 1981).
Zanzibar reported three different types of diseases affecting clove plantations. Fungus Valsa eugenia caused blocking of the vessels by tyloses of the tree and eventually died with dead leaves retained on the tree. Cryptosporella eugeniae, however, was a virus causing conspicuous red-brown staining of the wood and readily observable fructifications and then sudden death of the tree. Finally, both Saissetiea eugeniae (termites) and Oecopphylla smaragdina (red tree ants) caused considerable damages to clove trees (Purseglove, 1968).
Moreover, mass decline of cloves in Sumatra between 1968 and 1976 was reported due to Phytophthora cinnamony and Rickettsia like bacterium (RLB). Both pathogens were stem borers. They were discolored bands in the woods. The treatment of the tree with broad spectrum and specific pesticides and fumigation were inconclusive in controlling the diseases. However, farmers were encouraged to carefully plant clove trees together with other types. Until the new selection of cultivars were found, if the diseases kept occurring the land would had to be planted with totally different crops (Bennet et al., 1979).
Recent publication reported that Sumatran disease constantly kills up to 10% of mature trees each year in part of Sumatra and West Java, with an estimated annual crops loss of $US 25 million. Moreover, Psedomonas syzygii, Phyllosticta syzygium and Guigordia hevea have been identified as pathogens for clove trees and caused vascular discoloration and root decay and leaf blister blight, respectively (Guzman and Simonsma, 1999).
Historically, clove trading has been around long enough and it affects welfare of so many people world wide including small plantation holders, industrialists, economist and bureaucrats of many countries. For countries of Indonesia, Zanzibar, Madagascar, China, Malaysia, Tanzania, cloves is inevitably important for the economy of their country. One can only be skeptical that kretek cigarette is one of the most highly taxable product made partly of clove buds and stems.
The demand for cloves for foods, flavoring agents for cigarettes and other domestic/household products and industrial purposes has been stable if not inclined throughout the year and hence cloves will always occupy a segment of spice market.
Sustainable supply of cloves should be ensured, however, by healthy clove plantations. In order to have a healthy clove plantation, clove trees have to be placed in ecologically balanced environment where both the wild species and selected superior cultivars of Syzygium aromaticum are let live and can grow naturally. That way, plant pathogens are limited and under control. Also the use of herbicide, pesticide, and insecticide can only be afforded into a bare minimum. By doing so, plant – plant – human – animal interactions can be facilitated for much improved evolution.
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Created by Tumbur and Rainer (Economy Botany, Leiden 2001)