The Olive (Olea europaea) is a species of small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean region, from Lebanon, Syria and the maritime parts of Asia Minor and northern Iran at the south end of the Caspian Sea. Its fruit, the olive, is of major agricultural importance in the Mediterranean region as the source of olive oil.
The fruit is a small drupe 1–2.5 cm long, thinner-fleshed and smaller in wild plants than in orchard cultivars. Olives are harvested at the green stage or left to ripen to a rich purple colour (black olive). Canned black olives may contain chemicals that turn them black artificially.
The leafy branches of the olive tree, olive leaf as a symbol of abundance, glory and peace, were used to crown the victors of friendly games and bloody war. As emblems of benediction and purification, they were also ritually offered to deities and powerful figures: some were even found in Tutankhamen's tomb.
Olive oil has long been considered sacred; it was used to anoint kings and athletes in ancient Greece. It was burnt in the sacred lamps of temples as well as being the "eternal flame" of the original Olympic Games. Victors in these games were crowned with its leaves. Today it is still used in many religious ceremonies.
Pliny the Elder told of a sacred Greek olive tree that was 1600 years old. Several trees in the Garden of Gethsemane (from the Hebrew words "gat shemanim" or olive press) in Jerusalem are claimed to date back to the time of Jesus. Some Italian olive trees are believed to date back to Roman times, although identifying progenitor trees in ancient sources is difficult.
However, the age of an olive tree in Crete, claimed to be over 2,000 years old, has been determined on the basis of tree ring analysis. Another, on the island of Brijuni (Brioni), Istria in Croatia, a well-known olive tree has been calculated to be about 1,600 years old. It still gives fruit (about 30 kg per year), which is made into top quality olive oil.
A tree located in Santu Baltolu di Carana in Sardinia, Italy, named with respect as the Ozzastru by the inhabitants of the region, is claimed to be 3000 to 4000 years old according to different studies. In the same natural garden, a few other millenary trees can be admired.
The olive tree has been cultivated since ancient times as a source of olive oil, fine wood, olive leaf, and olives for consumption. The naturally bitter fruit is typically subjected to fermentation or cured with lye or brine to make it more palatable.
Green olives and black olives are washed thoroughly in water to remove oleuropein, a bitter carbohydrate. Sometimes they are also soaked in a solution of food grade sodium hydroxide in order to accelerate the process.
Green olives are allowed to ferment before being packed in a brine solution. American black ("California") olives are not fermented, which is why they taste milder than green olives.
It is not known when olives were first cultivated for harvest. Among the earliest evidence for the domestication of olives comes from the Chalcolithic Period archaeological site of Teleilat Ghassul in what is today modern Jordan.
The plant and its products are frequently referred to in the Bible, the Book of Mormon, the Qur'an, and by the earliest recorded poets. Farmers in ancient times believed olive trees would not grow well if planted more than a short distance from the sea; Theophrastus gives 300 stadia (55.6 km) as the limit. Modern experience does not always confirm this, and, though showing a preference for the coast, it has long been grown further inland in some areas with suitable climates, particularly in the southwestern Mediterranean (Iberia, northwest Africa) where winters are mild.
Olives are now cultivated in many regions of the world with Mediterranean climates, such as South Africa, Chile, Australia, Mediterranean Basin, Israel, Palestinian Territories and California and in areas with temperate climates such as New Zealand, under irrigation in the Cuyo region in Argentina which has a desert climate. They are also grown in the Córdoba Province, Argentina, which has a temperate climate with rainy summers and dry winters (Cwa); the climate in Argentina changes the external characteristics of the plant but the fruit keeps its original characteristics . Considerable research supports the health-giving benefits of consuming olives, olive leaf and olive oil (see external links below for research results).
The olive tree provides leaves, fruit and oil. Olive leaves are used in medicinal teas.
There are thousands of cultivars of the olive. In Italy alone at least three hundred cultivars have been enumerated, but only a few are grown to a large extent. The main Italian cultivars are 'Leccino', 'Frantoio' and 'Carolea'. None of these can be safely identified with ancient descriptions, though it is not unlikely that some of the narrow-leaved cultivars most esteemed may be descendants of the Licinian olive. The Iberian olives are usually cured and eaten, often after being pitted, stuffed (with pickled pimento, anchovies, or other fillings) and packed in brine in jars or tins.
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:
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. 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.
In general, a temperature below 14 °F (-10 °C) may cause considerable injury to a mature tree, but (with the exception of juvenile trees) a temperature of 16 °F (-9 °C) will normally cause no harm.
In southern Europe the olive harvest is in winter, 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; 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 olives used for oil. Table olive varieties are more difficult to harvest, as workers must take care not to damage the fruit; 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.
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.
A pest which spreads through olive trees is the black scale bug, a small black beetle that resembles a small black spot. They attach themselves firmly to olive trees and reduce the quality of the fruit; their main predators are wasps. The curculio beetle eats the edges of leaves, leaving sawtooth damage.
Rabbits eat the bark of olive trees and can do considerable damage, especially to young trees. If the bark is removed around the entire circumference of a tree it is likely to die.
In France and north-central Italy olives suffer occasionally from frost. Gales and long-continued rains during the gathering season also cause damage.
The ten largest producing countries, according to FAO, are all located in the Mediterranean region and produce 95% of the world's olives.
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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. In South Australia 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.