The olive is one of the earliest plants cited in recorded literature. Horace mentions it in reference to his own diet, which he describes as very simple: “Me pascunt olivae, me cichorea, me malvae”. Pliny the Elder told of a sacred Greek olive tree that was 1600 years old, while others claim that some of the specimens in the Garden of Gethsemane date back to the time of Christ. Some Italian olive trees have been credited with an antiquity reaching back to the Roman empire such as the Linza olive plants cited before bishop Ludovico de Pennis’ pastorale visit to Alliste on 11 May 1452; but the age of such ancient trees is doubtful during growth, and their identity with old descriptions still more difficult to establish. Lord Monboddo comments on the olive in 1779 as one of the foods preferred by the ancients and as one of the most perfect foods.
The olive has been used since ancient times for the making of olive oil and for eating of the fruit, which, being bitter in its natural state, are typically subjected to fermentation or cured with lye or brine to be made more palatable.
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 and by the earliest poets. The ancient agriculturists believed that the Olive would not succeed 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 (Syria, Iberia, northwest Africa) where winters are less severe.
Muhammad also mentions that the tree is blessed and recommends consumption and anointment of olive oil.
Olives are now culivated in many regions of the world such as Australia, New Zealand, and California. Considerable research has been done to support the health benefits of eating olives and olive oil.
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. Lax practices such as using olives 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.
The amount of oil contained in the fruit differs much in the various sorts; the pericarp usually yields from 60 to 70%.