Eucalyptus oils are obtained by distillation of the leaves ofEucalyptusand have aromas characteristic of the particular species used.
The oils are classified in the trade into three broad types accordingto their composition and main end-use: medicinal, perfumery and industrial.Of these, the most important in terms of volume of production and tradeis the medicinal type, characterised by a high cineole content in the oil.This, and the perfumery type, are discussed below. The so-called industrialoil, produced fromE. dives, now has a very small and diminishingmarket and is not discussed further.
The medicinal type of oil may be sold as such, neat, in pharmacies andother retail outlets or in the form of sprays, lozenges, cough sweets andointments or in formulation with other oils. It is used as an inhalantor chest rub to ease breathing difficulties, as a mouthwash in water torefresh or ease the throat, and as a skin rub to provide relief from achesand pains. Anti-plaque solutions in dental hygiene are a recent application.Although employed for medicinal purposes, the pleasant flavour and fragranceproperties of cineole-rich eucalyptus oils play an important role in theiracceptance and utilization on such a large scale. Eucalyptus oil is alsoused as a general disinfectant, cleaner and deodorizer about the house.
Of the two principal perfumery oils, that fromEucalyptus citriodorais produced in the greatest volume. It differs from the medicinal oilsin containing citrinellal, rather than cineole, as the major constituent.The oil is employed in whole form for fragrance purposes, usually in thelower cost soaps, perfumes and disinfectants, but also as a source of citrinellalfor the chemical industry. The citrinellal obtained by fractionation ofthe crude oil may be used as such as an aroma chemical or converted toother derivatives intended for fragrance use.
The only other perfumery oil produced in any quantity is that fromE.staigeriana. No single chemical predominates in the oil and it is usedin whole form for perfumery purposes. It has a lemon-type character.
World production and trade in eucalyptus oils is dominated by the People'sRepublic of China, which is the largest producer of both cineole-rich medicinaloils (about 70 percent of world output and trade) and perfumery oil (fromE.citriodora). It is not possible to quantify accurately total worlddemand for eucalyptus oils. The weakness of production statistics and ofdomestic consumption statistics in the producing country markets, especiallyfor such a large producer and consumer as the People's Republic of China,makes published trade statistics of limited value for analytical purposes.Furthermore, several importing countries such as Portugal, Spain and Australiaare also producers and processors of eucalyptus oils and re-export muchof what they import.
Notwithstanding these difficulties, total world production of medicinaltype eucalyptus oil in 1991 has been estimated at around 3000 tonnes, ofwhich approximately 2000 tonnes were exported (COPPEN and HONE, 1992).Production and exports ofE. citriodora oil, the main perfumeryoil, for 1991 are estimated at about 1500 tonnes and 500 tonnes, respectively.
Globally, the European Community is the largest importer of eucalyptusoils and recorded imports for the period 1984-90 are shown in Table 7.
It should be noted that medicinal and perfumery oils are not distinguishedin trade statistics.
Within Europe, France, Germany and the UK are the major markets foreucalyptus oil-based products. In 1990 their combined imports amountedto 1840 tonnes.
Imports into the United States, the largest single country market foreucalyptus oils (excluding the People's Republic of China and those countrieswhich re-export much of their imports after further processing), are shownin Table 8.
Changes and disruptions in Chinese patterns of trade and domestic usageof eucalyptus oils since 1989 have caused a fall in domestic offtake andan expansion of exports, the latter driven by a desire to earn foreignexchange. Although increasing, the world market for eucalyptus oil is notgrowing rapidly, and with no major new uses for it which could absorb largevolumes, opportunities for new producers are likely to rest mainly withmeeting local or regional needs rather than trying to compete in the widerinternational market.
The main producers and suppliers of cineole-type (medicinal) eucalyptusoil to the world market are shown in Table 9, together with estimates oftheir production and exports in 1991.
Under intense price pressure from Chinese oil, primary production inPortugal and Spain has decreased in recent years although both countriesremain significant exporters of eucalyptus oil products. The balance ofthe starting oil is imported, chiefly from the People's Republic of China.
Southern Africa is a major producing region for eucalyptus oil, mostof it from South Africa but a significant proportion from Swaziland. InSouth America, Chile and Brazil are the major producers, with smaller amountscoming from Bolivia, Uruguay and Paraguay.
Australia, the home ofEucalyptus and eucalyptus oil production,has declined in importance since its heyday in the 1940s. However, in theface of increasing production elsewhere in the world, the introductionof mechanized harvesting (see below) has enabled the Australian industryto become more efficient and it remains an important supplier of refinedand finished eucalyptus oil products (based partly on its own productionand partly on imports of crude or partially refined oil).
Production ofE. citriodora oil is also dominated by the People'sRepublic of China. In 1991 it is estimated that she accounted for approximatelytwo thirds, 1000 tonnes, of total production, of which, perhaps, 400 tonneswere exported. Brazil (500 tonnes) and India (50 tonnes) are the only otherproducers of this type of oil, with Brazil exporting about half of herproduction. Brazil is the only supplier to the world market ofE. staigerianaoil; production is of the order of 60 tonnes pa.
The value of eucalyptus oil for medicinal purposes lies in its cineolecontent, which largely determines, also, the price that it fetches. Nationaland international standards exist which specify the minimum cineole contentexpected of such oils and this is normally 70 percent (m/m). The intrinsiccomposition of the oil is largely determined by the species ofEucalyptusthat is distilled and for a few species (such asE. polybractea)the crude oil from the primary distillation of the leaves easily exceedsthis minimum requirement. For most eucalypts which are exploited, however,the crude oil has to be rectified to increase its cineole content. Theseoils then enter international trade. Chinese oil, for example, is commonlytraded as "eucalyptus oil 80 percent", referring to the fact that it containsat least 80 percent cineole.
Cineole-rich oils used strictly for medicinal purposes must satisfynational or international pharmacopoeia and this may introduce furtherrequirements for compliance, although this will be a task for the rectifierof the oil rather than the primary producer. CrudeE. smithii oil,for example, suffers from the disadvantage of containing a few percentof isovaleraldehyde and this adversely affects its odour. In order to meetpharmacopoeia standards the aldehyde content must be reduced by rectification.
For the perfumery oils, aroma characteristics are important but it isleft to the subjective assessment of the prospective buyer to decide whetherthe oil is acceptable in this respect. Published standards exist forE.citriodora oil and these usually specify that the aldehyde contentcalculated as citrinellal should not be less than 70 percent.
Price trends of both cineole-rich and perfumery oils have been greatlyinfluenced by the ample supplies of Chinese oils on the market in recentyears and the price at which they have been offered. In early 1994 theprice of standard grade Chinese 80 percent eucalyptus oil had fallen belowUS$3/kg from the US$6/kg level in 1989. Prices for cineole-rich oil ofPortuguese/Spanish origin are US$2-3 higher than Chinese prices becauseof the preference by end-users for these traditional sources. A new producerof eucalyptus oil, however, would need to compete, at least in the firstinstance, with Chinese oil.
It is possible that the next few years will see reduced Chinese exportsand a slow recovery in demand and prices, though eucalyptus oil will remainone of the lower priced essential oils.
Until the recent fall in prices, ChineseE. citriodora oil waslower priced than cineole-rich oil of Chinese origin. The situation hasnow reversed and in early 1994E. citriodora oil was being offeredby London dealers at US$3.35/kg.
Several hundreds of species ofEucalyptus have been shown to containvolatile oil, though probably fewer than 20 of these have ever been exploitedcommercially for oil production. Today, fewer than a dozen species areutilized in different parts of the world, of which six account for thegreater part of world production of eucalyptus oils.
Those species currently exploited, and the countries in which they areutilized, are listed below. (The use of parentheses indicates a minor producer.)Other species that have been used in the past includeE. cinerea(medicinal),E. cneorifolia (medicinal) andE. macarthurii(perfumery).
| Medicinal | |
| Eucalyptus globulus Labill. (Tasmanian blue gum) | People's Republic of China, Portugal, Spain, India, Brazil, Chile, (Bolivia, Uruguay, Paraguay) |
| E. smithii R. Baker (gully gum) | South Africa, Swaziland, (Zimbabwe) |
| E. polybractea R. Baker(syn. E. fruticetorumF. Muell. ex Miq.) (blue mallee) | Australia |
| E. exserta F. Muell. (Queensland peppermint) | People's Republic of China |
| E. radiata Sieber ex DC. (syn. E. australiana, E. radiata var. australiana) (narrow-leavedpeppermint) | (South Africa, Australia) |
| E. dives Schauer (cineole variant) (broad-leaved peppermint) | (Australia) |
| E. camaldulensis Dehnh. (syn. E. rostrata Schldl.) (river red gum) | (Nepal) |
| Perfumery | |
| E. citriodora Hook. (lemon-scented gum) | People's Republic of China, Brazil, India |
| E. staigeriana F. Muell. ex Bailey (lemon-scented ironbark) | Brazil |
Eucalypts vary in form from low shrubs and multi-stemmed trees less than10 m in height ("mallees") to large single-stemmed trees more than 60 mtall. The production of lignotubers is a characteristic of many speciesand this generally makes them respond to coppicing. On the death of theplant stem, either through fire or by cutting, dormant vegetative budswhich have been present in a tuberous mass at the base of the tree developand produce new stems. The ability to growEucalyptus under a coppicesystem of management is central to the economic production of oil.
The genusEucalyptus is native to Australia and some islandsto the north of it and consists of over 500 species of trees. These growunder a wide range of climatic and edaphic conditions in their naturalhabitat and is one reason for the successful introduction ofEucalyptusinto so many other countries in the world. Together withPinus,the two genera account for the larger part of exotic plantations in theAmericas, Europe, Africa and Asia.
Like pines, eucalypts are grown for timber or pulp but their fast-growingnature also makes them ideally suited as a fuelwood crop. In some casesthe favoured species for wood production (such asE. saligna andE.grandis, orE. tereticornis in India) are not suitable for oil.In other instances they are, and leaf oil may be obtained as a secondaryproduct from the plantings (as is the case forE. globulus plantedfor pulp in Portugal,E. citriodora grown for charcoal productionin Brazil andE. smithii utilized for mining timber in South Africa).
When leaf oil is to be a product of new eucalypt plantings the choice ofspecies will depend on the particular environmental conditions that prevailat the intended site. Although most species ofEucalyptus providean oil on distillation, its economic recovery requires the oil to be ofgood quality (at least 60-65 percent cineole in the case of a medicinal-typeoil) and produced in high yields. In practical terms, therefore, the choiceis likely to fall on one of the species already utilized (and listed above).
In Swaziland and South Africa,E. smithii has been found to growparticularly well under local conditions, producing large amounts of leafbiomass, and this has led to it being preferred for oil production overother species. In the same regionE. radiata, although it yieldsless biomass, gives a similar recovery of oil on a per hectare basis asE.smithii. Its better aroma characteristics, however, make it a specieswith much potential and it may in the future be more widely planted thanit is at present.
In Australia, the reduced level of oil production compared with 50 yearsago is a result of the inevitable rise in labour costs associated withsuch production rather than a loss of the trees themselves. In any case,as has been indicated, most eucalypts respond to coppicing and cuttingback of the natural stands is soon followed by the emergence of coppiceregrowth.
Eucalyptus leaf destined for oil production is obtained commercially byone of three methods:
- recovery of "waste" leaf from felled trees which have beengrown
primarily for their wood;
- short-rotation harvesting of plantations established specificallyfor
oil production. Under such a system of coppicing, plants are allowed
to grow for no more than about 20 months before cutting;
- regular harvesting of wild stands (peculiar to Australia).
In most cases, the branches trimmed from the stems of eucalypts that arefelled for timber, pulp or fuelwood production are left in the field aswaste or burnt; this also includes the shoots and side stems derived frompruning operations. Those countries which possess large areas of an oil-yieldingspecies are able to make use of this "waste" resource to produce oil. Thisis the case for the People's Republic of China, Portugal and Spain whichrecover oil fromE. globulus. The foliage should not be left onthe ground too long before transportation to the distillery or there isa risk of losing volatile oil.
Although the raw material itself (the foliage) may have very littlecost associated with it, any prospective producer of eucalyptus oil whois contemplating the utilization of "waste" leaf should ensure that thelogistics of collection are adequately considered. Labour and transportcosts are not insignificant.
Those species ofEucalyptus which respond well to coppicing maybe grown specifically for oil on a short-rotation cycle. In Swaziland,where oil is obtained fromE. smithii, the first cut is made 20-24months after planting. Subsequent cuts of the coppice regrowth are madeat approximately 16-month intervals, at which time the plants are 5-6 mtall. Harvesting may continue for many years and in Swaziland some areasofE. smithii are still being harvested after 20 years or more.
In Brazil, one producer of oils fromE. citriodora, E. globulusandE. staigeriana adopts a slightly different system of harvesting.Eighteen months after planting, the smaller branches are cut from the stem.This process is repeated every 6 months or so until the branches are toohigh to be reached (a period of about 3 years). The stem is then cut atabout knee height and two or three stems are allowed to grow over a periodof about 12 months, when the harvesting cycle is repeated.
The distillery is usually located within a reasonable distance of wherethe eucalypts are growing and foliage from the harvesting operation isdistilled either the same day or the following day.
The multi-stemmed, shrubby nature of coppicedE. polybractea offersan alternative means of leaf collection that is not labour intensive: mechanicalharvesting. This system of harvesting was developed in Australia as a meansof reducing labour costs and is used to harvest natural stands ofE.polybractea. The frequency of harvesting is between 18 months and 24months, at which time the shrubs are about 1 m high.
On a more limited scale in Australia,E. polybractea has beenplanted as a crop for oil production. The first harvest is usually madeafter 3 years with subsequent harvesting at 18-month intervals.
An additional advantage of the mechanical harvesting system is thatthe mobile "bin" into which the cut foliage is blown functions not onlyas a means of transporting it back to the distillery, but as a distillationvessel. By such means, double handling by way of unloading and reloadingof the leaf into a separate vessel is avoided. A steam line is simply connectedto the bottom of the bin, and a cover with a hole in the centre which allowsexit of the oil/water vapours during distillation is placed over the top.The vapours are led away through a flexible hose and then condensed andseparated in the normal manner.
Yields of oil from leaf vary somewhat between species but on a commercialscale are of the order of 1 percent on a "fresh" basis. (Note that "leaf"in this context includes the woody material of the branches which containslittle or no oil.) Of more relevance to the economics of production isthe yield of oil per hectare and this is dependent on the biomass productionas well as the oil yield from the leaf. Production fromE. smithiiin Swaziland yields approximately 15 tonnes/ha of leaf, corresponding toabout 150 litres/ha of oil.
The dependence of oil quality on species has already been referred to.There may also be marked differences in oil yield and quality within aspecies according to the provenance origin of the seed.E. camaldulensis,for example, has a very wide distribution in Australia, but only certainnorthern Queensland provenances (Petford, in particular) yield an oil whichmakes the species attractive as a source of medicinal oil. In extreme casesin their natural habitat, even trees within the same provenance may produceoils which are quite different to each other.E. dives is a well-knownexample and it is possible to obtain seed from cineole and piperitone variants.
Further small yield and compositional differences may arise from theuse of juvenile rather than adult leaf for distillation, though it is notgenerally practicable to attempt to separate different types of leaf ina commercial operation.
The enhancement of cineole content of the crude oil by a process of rectificationentails carrying out a fractional distillation under reduced pressure.Small producers of eucalyptus oils, for whom it is not economic to investin the equipment needed to do this, sell their crude oil to other, largerproducers or to rectifiers who are not, themselves, producers of crudeoil. An annual oil production of the order of 40-50 tonnes is the minimumscale of operation that would make rectification a viable option for aproducer.
Essentially pure cineole, termed "eucalyptol", is traded and used bysome end-users, and commands a higher price than the lower grades, butit is necessary to prepare this in a second step after rectification. Thecineole-rich fraction is frozen at -300?C to -400?C for up to 24 hoursand the recovered mixture, which contains unfrozen impurities (principallylimonene), is centrifuged. The liquid portion is thus removed and the frozenpart warmed to furnish eucalyptol.
Apart from any primary utilization of the stem wood if the oil is producedfrom "waste" leaf, it is still possible to make use of both spent leaf(that is, the material remaining after distillation of the oil) and secondarybiomass, even from operations involving short-rotation coppicing, and thisaspect should always be considered by a prospective new producer of eucalyptusoil.
Small coppice stems from which the foliage is trimmed for distillationcan be used as fuel, either for the boiler providing steam at the distilleryor for sale to others. Spent leaf can also be used as a boiler fuel althoughonly a portion of the total available will probably be consumed in thisway. The remainder may be returned to the fields to serve as a fertilizer(or a mulch if conditions require it) or it may be converted to compostand sold to provide an additional source of income.
Although present prices of eucalyptus oils are the lowest they have beenin recent years, this is not atypical of the fluctuations that occur inthe essential oil market and they may be expected, in due course, to recover.The advantage ofEucalyptus over most other essential oil-bearingtree crops is that it offers the possibility of genuine multipurpose utilization.Moreover, the trees can be grown on a large, plantation scale or on anindividual or communal woodlot system. The rapid growth of the trees meansthat income can be derived from sales of the stems for poles, fuelwoodor other purpose within a fairly short time (7-10 years) during which periodleaf can also be harvested for oil production.
A number of socio-economic studies have been published describing theexperiences of smallholder or cooperative groups who have includedEucalyptusspecies amongst the trees planted. In Africa,E. camaldulensis isoften planted, either alone or withAcacia, Gmelina or some otherspecies, usually as a source of poles and fuelwood, though they may alsoserve as shelterbelts and windbreaks. Utilization of waste leaf from PetfordE.camaldulensis for simultaneous oil production is therefore an optionbut more research is needed to examine the likely economic returns to thefarmer. In Kenya, and elsewhere, the supposed disadvantages of growingeucalypts (high water and nutrient consumption) have not been borne outin practice. Adverse effects of woodlots on neighbouring crops can be minimisedby careful consideration of positioning.
The intrinsic variability ofEucalyptus germplasm sources has alreadybeen discussed. The advantages to be gained from giving adequate attentionto selection of seed for planting cannot be over-emphasized. Over-hastyplanting of a species or provenance which is unsuited to local conditions,or does not produce an oil of acceptable quality or yield, will resultin failure.
Despite the large store of knowledge that is available on the cultivationof eucalypts for wood and pulp, further research is needed to maximizethe returns on eucalypts planted (solely or partly) for the productionof oil:
- Determination of biomass production. While information is often availableon the yields of oil to be expected from the leaf of particular speciesofEucalyptus, much less is known about the amount of leaf producedin the field, with which meaningful estimates can be made of productivity,i.e. oil yield per hectare per year. Specific areas requiring researchinclude the effects of spacing, fertilizer application and frequency andheight of coppicing on biomass/oil yields.
- Investigation of nutrient recycling. In cases where eucalypts aregrown specifically for oil on a short rotation, the long-term effects ofcontinued removal of biomass and possible nutrient depletion of the soilneed to be studied.
- Socio-economic studies of the effects of including oil productionin smallholder/cooperative ventures involving multipurpose eucalypts andwoodlots. To date, most work has related to wood use only.
- Some species deserve particular attention. In Africa and Asia,E.camaldulensis has great potential as a source of fuelwood/poles andoil. In Africa,E. smithii andE. radiata are high oil yielders.In very dry areasE. polybractea may have potential although itwould not be suitable for timber production.
BOLAND, D.J., BROPHY, J.J. and HOUSE, A.P.N. (eds) (1991)EucalyptusLeaf Oils.Use, Chemistry, Distillation and Marketing. 252 pp. Melbourne/Sydney:Inkata Press.
BOOTH, T.H. (1992) Where in the world? New climatic analysis methodsto assist species and provenance selection for trials.Unasylva,42(165), 51-57.
BROOKER, M.I.H. and KLEINIG, D.A. (1990)Field Guide to Eucalypts,Vols. 1 and 2. Melbourne/Sydney: Inkata Press.
CALDER, I. (1990) Eucalyptus not the villain after all.Overseas,No. 4, p 6. Wallingford, UK: Institute of Hydrology.
CONROY, C. (1992) Can eucalypts be appropriate for poor farmers?AppropriateTechnology, 19(1), 22-25.
COPPEN, J.J.W. and DYER, L.R. (1993)Eucalyptus and its Leaf Oils.An Indexed Bibliography. 205 pp. Chatham, UK: Natural Resources Institute.
COPPEN, J.J.W. and HONE, G.A. (1992)Eucalyptus Oils. A Review ofProduction and Markets. NRI Bulletin 56. 45 pp. Chatham, UK: NaturalResources Institute.
FAO (1979)Eucalypts for Planting. FAO Forestry Series No. 11.677 pp. Rome: FAO.
FAO (1988)The Eucalypt Dilemma. 26 pp. Rome: FAO.
GUSTAVSSON, S. and KIMEU, P. (1992)Socio-economic Evaluation ofEucalyptus Growing on Small-scale Farms in Vihiga Division, Kakamega District,Kenya: a Minor Field Study. International Rural Development CentrePublication No. 210. 41 pp. Swedish University of Agricultural Sciences.
HERGERT, H.J. and UIBRIG, H. (1991) Economics of a pole and fuelwoodproduction project in the Hararghe highlands, eastern Ethiopia. InProceedingsof the First International Symposium on Horticultural Economics in DevelopingCountries, Alemaya, Ethiopia, 16-23 July, 1989. Acta Horticulturae(270), 373-379.
ISO (1974) Oil ofEucalyptus citriodora.International StandardISO 3044-1974 (E). 2 pp. International Organization for Standardization.
ISO (1974) Oil of Australian Eucalyptus, 80 to 85 percent cineole content.International Standard ISO 3065-1974 (E). 2 pp.International Organizationfor Standardization.
ISO (1980) Oil ofEucalyptus globulus. International StandardISO 770-1980 (E). 2 pp.International Organization for Standardization.
ISO (1983) Rectified oil ofEucalyptus globulus Labillardière,Portugal.International Standard ISO 4732-1983 (E). 2 pp. InternationalOrganization for Standardization.
NEIL, P.E. (1987)Notes on Potential Multipurpose and Community ForestTree Species. Forest Research Report, Vanuatu, No. 11/87. 2 pp.
OSEMEOBO, G.J. (1989) An impact and performance evaluation of smallholderparticipation in tree planting, Nigeria.Agricultural Systems, 29(2),117-135.
PENFOLD, A.R. and WILLIS, J.L. (1961) Essential oils. pp. 245-281. InTheEucalypts. 551 pp. London: Leonard Hill.
POORE, M.E.D. and FRIES, C. (1985)The Ecological Effects of Eucalyptus.FAO Forestry Paper No. 59. 87 pp. Rome: FAO.
TURNBULL, J.W. (1991) Future use of Eucalyptus: opportunitiesand problems. pp. 2-27. InProceedings of IUFRO Symposium on IntensiveForestry: The Role of Eucalypts, Durban, 2-6 September, 1991. Vol.1. 595 pp. Pretoria: Southern African Institute of Forestry.
WHITE, K.J. (1988)Eucalyptus on small farms. pp. 86-96. InProceedingsof an International Workshop on Multipurpose Tree Species for Small-farmUse, Pattaya, Thailand, 2-5 November, 1987.
N.6 : Eucalyptus leaves awaiting distillation. Eucalyptus globulus,showingjuvenile
and adult leaves, Portugal [ J. Coppen, NRI ]
N 7 : Harvesting Eucalyptus smithii, Swaziland. First cut about 24months [ J. Coppen, NRI ]
N 8 : Eucalyptus leaves being loaded into stills for distillation.Eucalyptus smithii,
Swaziland [ J. Coppen, NRI ]
N 9 : Regularly coppiced natural stands of Eucalyptus polybractea
awaiting harvesting, Australia [ J. Coppen, NRI ]
Table 7
Imports of eucalyptus oil into the European Community, and sources,1984-90
(tonnes)
| Total | |||||||
| Of which from: | |||||||
| China | |||||||
| Portugal | |||||||
| Spain | |||||||
| Brazil | |||||||
| South Africa | |||||||
| Others | |||||||
Table 8
Imports of eucalyptus oil into the United States, 1984-90
(tonnes)
| Total |
| Total | ||
| Of which: | ||
| China, People's Rep. of | ||
| Portugal | ||
| India | ||
| South Africa | ||
| Australia | ||
| Swaziland | ||
| Chile | ||
| Spain | ||
| Others | ||
