Cultivation and uses

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. Green olives and black olives are soaked in a solution of sodium hydroxide and then washed thoroughly in water to remove oleuropein, a naturally bitter carbohydrate.

Subspecies

There are at least five natural subspecies distributed over a wide range:

Cultivars

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 that are 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, onion, or other garnishes) and jarred in fresh brine.

Growth and propagation

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.

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.

Traditional Fermentation of Table Olives

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. Olives are often sold at markets in 10kg 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 colour), through to full purple black ripeness. The olives are soaked in water to wash them, and drained. About 7 litres of room temperature water is added to the fermentation container, and 800g 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 800g of salt is in a 8kg mixture of salt and water and vinegar). Each olive is given a single deep slit with a small knife if they are small, or up to three slits per fruit if they are 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. Oleuropein is a useful antioxident in the human diet. The olives become reasonably acceptable after 2 weeks to a month, and may develop full maturity in three months. This is happening in winter as they are harvested in autumn. Green olives should be firm in texture once fermented and black olives will be softer. Olives produced in this way will normally be safe and delicious as is. Should you want to present your olives with other flavours they can be marinated in, or stuffed with, a great variety of herbs, spices, and flavours such as additional olive oil, fetta, capsicum (pimento), chili, lemon zest, lemon juice, garlic, wines, vinegars, and anchovies. This method has many variations and may include longer washes in water, up to a week, and multiple changes of salt solution.

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. savastanoi 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.

Economy

Production

The first ten countries of production, all located in the mediterranean region, represent together 95 % of the world production of olives.

References

See also

• Phytonutrient
• Polyphenol antioxidant