Oliven

Oliven
Nomenklatur
Olea europaea
Populærnavn
oliven, oliventre
Hører til
oliventrær, oljetrefamilien, Lamiales
Økologi
Habitat:		terrestrisk
Utbredelse:		opprinnelig fra områder øst i Middelhavet

Oliven (Olea europaea) er en art av små trær i oljetrefamilien, som har sin opprinnelse fra kyststrøkene i de østlige deler av Middelhavet, fra Libanon til kysten av Lilleasia og de nordlige deler av Iran. Olivenfrukten, som kommer fra denne arten, er et av middelhavslandenes viktigste landbruksprodukter, da det brukes til å lage olivenolje.

Beskrivelse

Olivenen er et eviggrønt tre eller busk fra områder rundt Middelhavet, Asia og deler av Afrika. Det er forholdsvis kort og tykt, og oppnår sjelden en høyde på over 8–15 meter.

De sølvgrønne bladene har avlang form, med en normallengde på 4–10 cm og bredde på 1–3 cm. Trestammen er vanligvis krokete og bøyd.

Blomstene er små og hvite med firekløyvet beger og krone, samt to pollenbærere og tolappet stigma. De kommer normalt frem på fjorårets tre, i klaser som springer ut fra bladakselen.

Frukten er en liten steinfrukt med 1–2.5 cm lengde og nokså tynt fruktkjøtt. Den blir normalt større ved dyrking i drivhus enn ved tradisjonell dyrking. Oliven høstes ved grønnstadiet eller etterlates for å modne til en rik purpurfarge (svart oliven). Hermetisert svart oliven kan inneholde kjemikalier som gir dem en kunstig svart farge.

Historie

Se også olivenoljens historie

Olivenen er en av de mest omtalte plantene i skriftlig tid. I poeten Homer sitt episke dikt Odysseen, kryper Odyssevs under to olivenknopper som vokser fra en enkeltstamme. Den romerske poeten Horats nevner den også i forbindelse med sitt eget kosthold, som han beskriver som meget enkelt: "For min del gir oliven, endivier og kattoster meg næring." Lord Monboddo beskrev oliven i 1779 som en av de mest foretrukne matvarene i oldtiden, og omtalte den også som en av de mest perfekte.

Gamle trær

Plinius den eldre talte om et hellig gresk oliventre som var over 1600 år gammelt. Det hevdes at flere av trærne i Getsemanehagen (fra hebraisk «gat shemanim», som betyr «oljepresse») i Jerusalem kan dateres til Jesu tid. Det antas også at noen italienske oliventrær kan dateres til romertiden, selv om det er vanskelig å identifisere stamtrær i antikke kilder.

Derimot har det blitt antydet at alderen på et oliventre i Kreta er over 2,000 år gammelt, på grunnlag av en treringdatering. I Istria i Kroatia, på øya Brijuni, står et velkjent oliventre som etter beregningene skal være omtrent 1,600 år gammelt. Det er fortsatt fruktbart (omtrent 30 kg per år), og brukes til å lage høykvalitets olivenolje. Oliventreet er et av symbolene for den greske gudinne Athene, og nevnes hyppig både i Bibelen og Koranen.

Dyrkning og bruk

Se også Oliven (frukt)

Et eksempel på svart oliven.

Olivenen har blitt dyrket siden oldtiden som en kilde til olivenolje og fint treverk, samt oliven til konsum. Den naturlig bitre frukten blir normalt gjæret eller behandlet med lut eller saltlake for å gjøre den mer velsmakende.

Grønn oliven og svart oliven blir lagt i en slags natriumhydroksid og skylt grundig i vann for å fjerne det bitre karbohydratet oleuropein.

Grønn oliven gjæres før de blir pakket inn i en lakefylt innpakning. Amerikansk svart oliven («California») blir ikke gjæret, noe som er grunnen til at de smaker mildere enn grønne olivener.

Det er ikke kjent når olivener først ble dyrket for høsting. Et av de første bevisene for utnyttelse av oliven kommer fra kobberalderen på det arkeologiske stedet Teleilat Ghassul, som i dag er det moderne Jordan.

Planten blir ofte nevnt i Bibelen, Koranen og av de første kjente poetene. Bønder i oldtiden trodde at oliventrær ikke ville gro skikkelig dersom de ble plantet langt unna sjøen; Theofrastos angir 300 stadia (55.6 km) om grensen. Nyere erfaringer støtter ikke alltid denne påstanden, for selv om kysten foretrekkes har det i lang tid blitt dyrket på innlandet i områder med passende klima, spesielt i det sørvestlige Middelhavet (Iberia og det nordvestlige Afrika) hvor vintrene er mildere.

Olivenplantasje i Andalucía, Spania.

Oliven blir nå dyrket i mange av verdens regioner, slik som Sør-Afrika, Australia, New Zealand, Middelhavslandene og California. Omfattende forskning har konkludert med at det oppnås helsefordeler av å konsumere olivener og olivenolje.

Oliventreet avgir blader, frukt og olje. Olivenblader brukes i medisinske teer.

Underarter

Det finnes minst fem naturlige underarter av Olea europaea i verden:

• europaea (Europa)
• cuspidata (fra Eritrea og Etiopia sørover mot Øst-Afrika, også i Iran til Kina)
• guanchica (Kanariøyene)
• maroccana (Marokko)
• laperrinei (Algerie, Sudan, Niger)

Kultivarer

Lite oliventre

Stort oliventre

Løvblad

Stammen

Olivenblomster

En ung olivenplante som spirer fra et frø

Fil:Olivodom.jpg Storslagent tre i Puglia (Sør-Italia)

Det eksisterer tusenvis av kultivarer av oliventreet. Bare i Italia finnes det minst 300 kjente, selv om bare noen få av dem dyrkes i stort omfang. De vanligste italienske versjonene er Leccino, Frantoio og Carolea. Ingen av disse kan med sikkerhet gjenkjennes med urgamle beskrivelser, men det er ikke usannsynlig at noen av de smalbladede kultivarene kan ha sitt opphav i den licinianske olivenen. Iberisk oliven blir normalt saltet og spist, ofte etter å ha blitt uthulet, fylt (med syltet pimiento, løk eller annen garnityr) og lagt i glass fylt med lake.

Since many cultivars are self sterile or nearly so, they are generally planted in pairs with a single primary cultivar and a secondary cultivar selected for its ability to fertilize the primary one, for example, 'Frantoio' and 'Leccino'. In recent times, efforts have been directed at producing hybrid cultivars with qualities such as resistance to disease, quick growth and larger or more consistent crops.

Some particularly important cultivars of olive include:

• 'Manzanillo', a large, rounded-oval fruit, with purple-green skin. Rich taste and thick pulp. A prolific bearer, grown around the world.
• 'Frantoio' and 'Leccino'. These cultivars are the principal participants in Italian olive oils from Tuscany. Leccino has a mild sweet flavour while Frantoio is fruity with a stronger aftertaste. Due to their highly valued flavour, these cultivars have been migrated and are now grown in other countries.
• 'Arbequina' is a small, brown olive grown in Catalonia, Spain. As well as being used as a table olive, its oil is highly valued.
• 'Empeltre' is a medium sized, black olive grown in Spain. They are used both as a table olive and to produce a high quality olive oil.
• 'Kalamata' is a large, black olive, named after the city of Kalamata, Greece, used as a table olive. These olives are of a smooth and meatlike taste.
• 'Koroneiki' originates from the southern Peloponese, around Kalamata and Mani in Greece. This small olive, though difficult to cultivate, has a high oil yield and produces olive oil of exceptional quality.
• 'Pecholine' or 'picholine' originated in the south of France. It is green, medium size, and elongated. Their flavour is mild and nutty.
• 'Lucques' originated in the south of France (Aude département). They are green, of a large size, and elongated. The stone has an arcuated shape. Their flavour is mild and nutty.
• 'Souri' (Syrian) originated in Lebanon and is widespread in the Levant. It has a high oil yield and exceptionally aromatic flavour.
• 'Nabali' is a Palestinian cultivar also known locally as 'Baladi', which along with 'Souri' and 'Malissi' are considered to produce among the highest quality olive oil in the world.
• 'Barnea' is a modern cultivar bred in Israel to be disease resistant and to produce a generous crop. It is used both for oil and for table olives. The oil has a strong flavour with a hint of green leaf. Barnea is widely grown in Israel and in the southern hemisphere, particularly in Australia and New Zealand.
• 'Maalot' is another modern, disease-resistant, Eastern Mediterranean cultivar derived from the North African 'Chemlali' cultivar. The olive is medium sized, round, has a fruity flavour and is used almost exclusively for oil production.
• 'Mission' originated on the California Missions and is now grown throughout the state. They are black and generally used for table consumption.

Growth and propagation

Olive trees show a marked preference for calcareous soils, flourishing best on limestone slopes and crags, and coastal climate conditions. They tolerate drought well, thanks to their sturdy and extensive root system. Olive trees can be exceptionally long-lived, up to several centuries, and can remain productive for as long, provided they are pruned correctly and regularly.

The olive tree grows very slowly, but over many years the trunk can attain a considerable diameter. A. P. de Candolle recorded one exceeding 10 m in girth. They can possibly reach great age and the trees rarely exceed 15 m in height, and are generally confined to much more limited dimensions by frequent pruning. The yellow or light greenish-brown wood is often finely veined with a darker tint; being very hard and close-grained, it is valued by woodworkers.

The olive is propagated in various ways, but cuttings or layers are generally preferred; the tree roots easily in favourable soil and throws up suckers from the stump when cut down. However, yields from trees grown from suckers or seeds are poor; it must be budded or grafted onto other specimens to do well (Lewington and Parker, 114). Branches of various thickness are cut into lengths of about 1 m and, planted deeply in manured ground, soon vegetate; shorter pieces are sometimes laid horizontally in shallow trenches, when, covered with a few centimetres of soil, they rapidly throw up sucker-like shoots. In Greece, grafting the cultivated tree on the wild form is a common practice. In Italy, embryonic buds, which form small swellings on the stems, are carefully excised and planted beneath the surface, where they grow readily, their buds soon forming a vigorous shoot.

Occasionally the larger boughs are marched, and young trees thus soon obtained. The olive is also sometimes raised from seed, the oily pericarp being first softened by slight rotting, or soaking in hot water or in an alkaline solution, to facilitate germination.

Where the olive is carefully cultivated, as in Languedoc and Provence, the trees are regularly pruned. The pruning preserves the flower-bearing shoots of the preceding year, while keeping the tree low enough to allow the easy gathering of the fruit. The spaces between the trees are regularly fertilized. The crop from old trees is sometimes enormous, but they seldom bear well two years in succession, and in many instances a large harvest can only be reckoned upon every sixth or seventh season.

A calcareous soil, however dry or poor, seems best adapted to its healthy development, though the tree will grow in any light soil, and even on clay if well drained; but, as remarked by Pliny, the plant is more liable to disease on rich soils, and the oil is inferior to the produce of the poorer and more rocky ground.

Fruit harvest and processing

Most olives today are harvested by shaking the boughs or the whole tree. Another method involves standing on a ladder and "milking" the olives into a sack tied around the harvester's waist. Using olives found lying on the ground can result in poor quality oil. In southern Europe the olive harvest is in the winter months, continuing for several weeks, but the time varies in each country, and also with the season and the kinds cultivated. A device called the oli-net wraps around the trunk of the tree and opens to form an umbrella like catcher to catch fruit that is picked. Workers can then harvest the fruit without the weight of the load around their neck. Another device, the oliviera, is an electronic tool that connects to a battery. The oliviera has large tongs that are spun around quickly, removing fruit from the tree. This method is used for olive oil variety olives. Table olive varieties are more difficult to harvest, as workers must take caution not to damage the fruit in any way. Picking baskets that hang around the worker's neck are used.

The amount of oil contained in the fruit differs greatly in the various cultivars; the pericarp is usually 60–70% oil. Typical yields are 1.5-2.2 kg of oil per tree per year.

Traditional fermentation

Olives freshly picked from the tree contain phenolic compounds and a unique glycoside, oleuropein, which makes the fruit unpalatable for immediate consumption. There are many ways of processing olives for table use. Traditional methods use the natural microflora on the fruit and procedures which select for those that bring about fermentation of the fruit. This fermentation leads to three important outcomes: the leaching out and breakdown of oleuropein and phenolic compounds; the creation of lactic acid, which is a natural preservative; and a complex of flavoursome fermentation products. The result is a product which will store with or without refrigeration.

One basic fermentation method is to get food grade containers, which may include plastic containers from companies which trade in olives and preserved vine leaves. Many bakeries also recycle food grade plastic containers which are well sized for olive fermentation; they are 10 to 20 litres in capacity. Freshly picked olives are often sold at markets in 10 kg trays. Olives should be selected for their firmness if green and general good condition. Olives can be used green, ripe green (which is a yellower shade of green, or green with hints of color), through to full purple black ripeness. The olives are soaked in water to wash them, and drained. 7 litres (which is 7 kg) of room temperature water is added to the fermentation container, and 800 g of sea salt, and one cup (300g) of white vinegar (white wine or cider vinegar). The salt is dissolved to create a 10% solution (the 800 g of salt is in an 8 kg mixture of salt and water and vinegar). Each olive is given a single deep slit with a small knife (if small), or up to three slits per fruit (if large, eg 60 fruit per kg). If 10 kg of olives are added to the 10% salt solution, the ultimate salinity after some weeks will be around 5 to 6% once the water in the olives moves into solution and the salt moves into the olives. The olives are weighed down with an inert object such as a plate so they are fully immersed and lightly sealed in their container. The light sealing is to allow the gases of fermentation to escape. It is also possible to make a plastic bag partially filled with water, and lay this over the top as a venting lid which also provides a good seal. The exclusion of oxygen is useful but not as critical as when grapes are fermented to produce wine. The olives can be tasted at any time as the bitter compounds are not poisonous, and oleuropein is a useful antioxidant in the human diet.

The olives are edible within 2 weeks to a month, but can be left to cure for up to three months. Green olives will usually be firmer in texture after curing than black olives. Olives can be flavored by soaking them in various marinades, or removing the pit and stuffing them. Herbs, spices, olive oil, feta, capsicum (pimento), chili, lemon zest, lemon juice, garlic cloves, wine, vinegar, juniper berries, and anchovies are popular flavorings. Sometimes the olives are lightly cracked with a hammer or a stone to trigger fermentation. This method of curing adds a slightly bitter taste.

Pests and diseases

A fungus Cycloconium oleaginum can infect the trees for several successive seasons, causing great damage to plantations. A species of bacterium, Pseudomonas savastanoi pv. oleae induces tumour growth in the shoots, and certain lepidopterous caterpillars feed on the leaves and flowers, while the main damage is made by the olive-fly attacks to the fruit. In France and north-central Italy olives suffer occasionally from frost. Gales and long-continued rains during the gathering season also cause damage. Another pest which spreads through olive trees is the black scale bug. Black scale is a small black beetle that resembles a small black spot. They attach themselves firmly to olive trees and reduce the quality of the fruit. The main predator of black scale is wasps.

Economy

Olive output in 2005

Production

Olive is the most extensively cultivated fruit crop in the world. Its cultivation areas has tripled in the past 44 years, passing from 2.6 to 8.5 million of hectares.

The first ten countries of production, as per FAO, all located in the Mediterranean region, represent together 95% of the world production of olives.

Main countries of production (Year 2003)

Rank	Country/Region	Production (in tons)	Cultivated area (in hectares)	Yield (q/Ha)
—	World	17,317,089	8,597,064	20.1
1	Spain	6,160,100	2,400,000	25.7
2	Italy	3,149,830	1,140,685	27.6
3	Greece	2,400,000	765,000	31.4
4	Turkey	1,800,000	594,000	30.3
5	Syria	998,988	498,981	20.0
6	Tunisia	500,000	1,500,000	3.3
7	Morocco	470,000	550,000	8.5
8	Egypt	318,339	49,888	63.8
9	Algeria	300,000	178,000	16.9
10	Portugal	280,000	430,000	6.5
11	Lebanon	180,000	230,000	4.5

Olive as an invasive weed

Since its first domestication, Olea europaea has been spreading back to the wild from planted groves. Its original wild populations in southern Europe have been largely swamped by feral plants.

In some other parts of the world where it has been introduced, most notably South Australia, the Olive has become a major woody weed that displaces native vegetation. Its seeds are spread by the introduced Red Fox and by many bird species including the European Starling and the native Emu into woodlands where they germinate and eventually form a dense canopy that prevents regeneration of native trees.

References

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