The fruit of the olive tree

A. Olive trees (Olea europaea), which are widely distributed across the Mediterranean region, Africa and Asia, have long represented wealth, abundance, power and peace.

The olive has been a symbol of the Mediterranean since time immemorial and has a reputation for long life, nourishment and its ability to thrive in tough conditions. There are claims of 1600-year-old trees still producing fruit.

B. The tree's primary product, olive oil, is revered throughout the world for its distinctive flavour. Homer called it 'liquid gold'. In Ancient Greece athletes rubbed olive oil over their bodies and winning competitors received no trophies or medals - instead the symbol of supreme honour was the olive wreath placed on their heads.

C. Olea europaea is an evergreen shrub or tree, which grows up to 15m tall. It is slow to mature but can live for hundreds of years. The leaves are borne in opposite pairs. The leaves are evergreen, 3 to 9cm long, elliptic, and silvery in appearance. The flowers are borne in axillary clusters, with a four-lobed calyx, and a four-lobed corolla. The two stamens (male parts) project beyond the mouth of the flower. The fruit has a hard endocarp (the olive stone), which is surrounded by a fleshy, edible mesocarp.

D. Grown in the Mediterranean for over 5000 years, the olive has shaped the landscape and culture of the region: 00% of all olives are produced in the Mediterranean. It is the region's most versatile and valuable crop with the fruit, oil and leaves having been used for food. fuel, medicine and embalming.

E. The birth of olive-farming is shrouded in the mists of time. Discoveries of olive stones at archaeological sites in the Middle East show at least 20 000 years of use and by 5000 years ago olives had been taken into cultivation and spread throughout the Levant. Domestication may have taken place in the eastern Mediterranean region, or in the region of the Nile Delta where the climate of the time would have been more suitable for cultivation. Today, there are thought to be around 1000 million olive trees in the world.

F. The harvesting of the olives occurs in autumn. If they are to become table olives, they are soaked in water for five days to extract the bitter phenolic compounds such asoleuropein. The fruit is then cured in brine for around four weeks. Green olives are unripe, whereas black olives are ripe and less bitter. Olives are eaten as snacks or appetisers with a variety of accompaniments, and are a key ingredient of Mediterranean cooking.

G. The oil is obtained from the fruit shortly after harvesting. The fruit is cleaned and processed into a paste from which the oil is extracted. Olive oil is classified according to the production method and the oleic acid content. A refined olive oil is obtained with the use of heat or solvent extraction and requires further processing to yield edible oil (it contains up to 3.3% oleic acid). The leftover cake is used as a source of inedible industrial-grade oil (containing more than 3.3% oleic acid), and is also used in livestock feed and compost.

H. The oil is used for food, cooking and for a multitude of therapeutic purposes. The safe dosage for adults is two tablespoons (28g) of olive oil per day. Evidence suggests that people whose diets include olive oil have a reduced risk of developing certain cancers. Likewise, a diet rich in olive oil (and low in saturated fats) is associated with reduced risk of cardiovascular disease, high cholesterol levels and high blood pressure.

I. The beneficial qualities of olive oil have been attributed to the fatty-acid composition and the presence of phenolic compounds, which seem to have antioxidant, vasodilating, anti platelet and anti-inflammatory effects. At the Botanical Gardens in Kew in London, investigations are being carried out on how the waste products of olive oil production could be used as sources of compounds for medicines to treat cardiovascular disease.

J. In the Aitxsretum Nursery at Kew young olive plants are grown from seed. It has been noted that germination is spasmodic, taking from a few weeks to a few months. The compost used as a growing medium is an open, gritty, free-draining mix. The seedlings are pricked out into 'air pots'. Air pots prevent the plants from becoming pot-bound by encouraging the roots to grow outwards rather than spiralling. Planting out into the required position in the garden can be carried out straight from the air pot. The glasshouse zone in which the seedlings are grown is kept at a minimum temperature of 5‘C. Only natural light is provided. The young plants are well watered and not allowed to dry out.