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Olive Tree




The origin and expansion of the olive tree

  The origin of the olive tree is lost in time, coinciding and mingling with the expansion of the Mediterranean civilisations which for centuries governed the destiny of mankind and left their imprint on Western culture.

Olive leaf fossils have been found in Pliocene deposits at Mongardino in Italy. Fossilised remains have been discovered in strata from the Upper Paleolithic at the Relilai snail hatchery in North Africa, and pieces of wild olive trees and stones have been uncovered in excavations of the Chalcolithic period and the Bronze Age in Spain. The existence of the olive tree therefore dates back to the twelfth millennium BC.

The wild olive tree originated in Asia Minor where it is extremely abundant and grows in thick forests. It appears to have spread from Syria to Greece via Anatolia (De Candolle, 1883) although other hypotheses point to lower Egypt, Nubia, Ethiopia, the Atlas Mountains or certain areas of Europe as its source area. Caruso for that reason believed it to be indigenous to the entire Mediterranean Basin and considers Asia Minor to have been the birthplace of the cultivated olive some six millennia ago. The Assyrians and Babylonians were the only ancient civilisations in the area who were not familiar with the olive tree.

Taking the area that extends from the southern Caucasus to the Iranian plateau and the Mediterranean coasts of Syria and Palestine (Acerbo) to be the original home of the olive tree, its cultivation developed considerably in these last two regions, spreading from there to the island of Cyprus and on towards Anatolia or from the island of Crete towards Egypt.

In the 16th century BC the Phoenicians started disseminating the olive throughout the Greek isles, later introducing it to the Greek mainland between the 14th and 12th centuries BC where its cultivation increased and gained great importance in the 4th century BC when Solon issued decrees regulating olive planting.

From the 6th century BC onwards, the olive spread throughout the Mediterranean countries reaching Tripoli, Tunis and the island of Sicily. From there, it moved to southern Italy. Presto, however, maintained that the olive tree in Italy dates back to three centuries before the fall of Troy (1200 BC). Another Roman annalist (Penestrello) defends the traditional view that the first olive tree was brought to Italy during the reign of Lucius Tarquinius Priscus the Elder (616 - 578 BC), possibly from Tripoli or Gabes (Tunisia). Cultivation moved upwards from south to north, from Calabria to Liguria. When the Romans arrived in North Africa, the Berbers knew how to graft wild olives and had really developed its cultivation throughout the territories they occupied.

The Romans continued the expansion of the olive tree to the countries bordering the Mediterranean, using it as a peaceful weapon in their conquests to settle the people. It was introduced in Marseilles around 600 BC and spread from there to the whole of Gaul. The olive tree made its appearance in Sardinia in Roman times, while in Corsica it is said to have been brought by the Genoese after the fall of the Roman Empire.

Olive growing was introduced into Spain during the maritime domination of the Phoenicians (1050 BC) but did not develop to a noteworthy extent until the arrival of Scipio (212 BC) and Roman rule (45 BC). After the third Punic War, olives occupied a large stretch of the Baetica valley and spread towards the central and Mediterranean coastal areas of the Iberian Penisula including Portugal. The Arabs brought their varieties with them to the south of Spain and influenced the spread of cultivation so much that the Spanish words for olive (aceituna), oil (aceite), and wild olive tree (acebuche) and the Portuguese words for olive (azeitona) and for olive oil (azeite), have Arabic roots.

With the discovery of America (1492) olive farming spread beyond its Mediterranean confines. The first olive trees were carried from Seville to the West Indies and later to the American Continent. By 1560 olive groves were being cultivated in Mexico, then later in Peru, California, Chile and Argentina, where one of the plants brought over during the Conquest - the old Arauco olive tree - lives to this day.

In more modern times the olive tree has continued to spread outside the Mediterranean and today is farmed in places as far removed from its origins as southern Africa, Australia, Japan and China. As Duhamel said, "the Mediterranean ends where the olive tree no longer grows", which can be capped by saying that "There where the sun permits, the olive tree takes root and gains ground".


About olives


The olive fruit is a drupe. It has a bitter component (oleuropein), a low sugar content (2.6-6%) compared with other drupes (12% or more) and a high oil content (12-30%) depending on the time of year and variety.

These characteristics make it a fruit that cannot be consumed directly from the tree and it has to undergo a series of processes that differ considerably from region to region, and which also depend on variety. Some olives are, however, an exception to this rule because as they ripen they sweeten right on the tree, in most cases this is due to fermentation. One case in point is the Thrubolea variety in Greece.

Oleuropein, which is distinctive to the olive, has to be removed as it has a strong bitter taste: it is not, however, pernicious to health. Depending on local methods and customs, the fruit is generally treated in sodium or potassium hydroxide, brine or successively rinsed in water.




SIZE: The olive's suitability for table consumption is a function of its size, which is important to presentation. Olives between 3 and 5 g are considered medium-sized, while those weighing over 5 g are large.

SHAPE: Fruits that are more or less spherical in shape usually sell best, although some elongated ones also find favour.

STONE: The stone should come away easily from the flesh and a flesh:stone ratio of 5 to 1 is acceptable; the higher this ratio the better the commercial value of the olives.

SKIN: The skin of the fruit should be fine, yet elastic and resistant to blows and to the action of alkalis and brine.

SUGAR CONTENT: A high sugar content in the flesh is an asset. The lowest acceptable level is 4%, especially in olives that undergo fermentation.

OIL CONTENT: Oil content should be as low as possible because in many cases it impairs the keeping properties and consistency of the processed fruit. Only in certain types of black olives is a medium to high oil content desirable.


Green olives


Green olives are obtained from olives harvested during the ripening cycle when they have reached normal size, but prior to colour change. They are usually hand picked when there is a slight change in hue from leaf-green to a slightly yellowish green and when the flesh begins to change consistency but before it turns soft. Colour change should not have begun. Trials have been run to machine harvest table olives, but owing to the high percentage of bruised fruit they had to be immersed in a diluted alkaline solution while still in the orchard.


Recently harvested, the olives are taken to the plant for processing on the same day if possible.

How are they processed?

Green olives are processed in two principal ways: with fermentation (Spanish type) and without fermentation (Picholine or American type).


Spanish or Sevillian style

The olives are treated in a diluted lye solution (sodium hydroxide) to eliminate and transform the oleuropein and sugars, to form organic acids that aid in subsequent fermentation, and to increase the permeability of the fruit. The lye concentrations vary from 2% to 3.5%, depending on the ripeness of the olives, the temperature, the variety and the quality of the water. The treatment is performed in containers of varying sizes in which the solution completely covers the fruit. The olives remain in this solution until the lye has penetrated two thirds of the way through the flesh. The lye is then replaced by water, which removes any remaining residue and the process is repeated. Lengthy washing properly eliminates soda particles but also washes away soluble sugars which are necessary for subsequent fermentation.

Fermentation is carried out in suitable containers in which the olives are covered with brine. Traditionally, this was done in wooden casks. More recently, larger containers have come into use that are inert on the inside. The brine causes the release of the fruit cell juices, forming a culture medium suitable for fermentation. Brine concentrations are 9-10% to begin with, but rapidly drop to 5% owing to the olive's higher content of interchangeable water.

At first Gram-negative bacteria multiply, but after a week and a half they disappear. They are a consequence of contamination produced in the plant installations, and in the atmosphere and brine and can be avoided by stepping up hygiene measures. At a pH level of 6 and upwards, lactobacilli develop massively until the Gram-negatives disappear and the brine attains a pH of 4.5. There is a predominance of Lactobacillus plantarum which produces lactic acid from glucose almost by itself. When the fermentable matter is spent, acid formation ceases. Yeasts appear together with the lactobacilli. Fermentative yeasts do not cause deterioration but oxidant yeasts consume lactic acid and raise the pH level and may therefore jeopardise the process.

Under certain conditions normal fermentation processes can be altered by the presence of undesirable microorganisms which can transmit poor organoleptic properties to the olives or impair their keeping properties. Gas pocket fermentation is caused by the Gram-negative bacilli in the first stage of fermentation, but can be controlled by intensifying hygiene precautions when the olives are delivered to the plant, as well as during lye treatment and washing. If gas pockets still appear in spite of these measures, the pH level can be lowered to 4 by adding an acid. Butyric fermentation is well controlled by ensuring the proper pH level. Putrid fermentation is caused by poorly-kept containers and bad water. Lastly, there is a type of deterioration known by its Spanish name of "zapatería" (cobbler's) which produces an unpleasant taste and odour at the end of the fermentation process, often coinciding with rising temperatures in the spring or early summer. It is produced by bacteria belonging to the Clostridium and Propioni-bacterium genus. The right combination of brine concentration and pH level (5% salt and 4.5 pH) helps to control fermentation processes.

When properly fermented, olives keep for a long time. If they are in casks, the brine level must be topped up. At the time of shipment, the olives have to be classified for the first or second time as the case may be. The original brine is replaced and the olives are packed in barrels and tin or glass containers. Sometimes they are stoned (pitted) or stuffed with anchovies, pimento, etc.

The most commonly used varieties are Manzanillo, Gordal and Moroccan Picholine

Picholine style

Olives belonging to the Picholine variety from Languedoc and Lucques in southern France are prepared in this manner, as are other varieties from Morocco and Algeria.

The bitterness of the olives is removed by treating them in a 3-3.5º B lye solution in which they are left for 8 to 72 hours until the lye has penetrated three-quarters of the way through the flesh. They are rinsed several times over the next day or two, and then placed in a 5/6% brine solution for two days. A second 7% brine solution is prepared, and acidity is corrected with citric acid (pH 4.5). After 8-10 days they are ready to be eaten and retain their intense green colour. Sometimes the consignment has to be postponed, and it is necessary to store the olives. This is easy, as long as temperatures do not rise. The olives can stay in an 8% brine solution until spring, but then it has to be raised to 10%. In larger installations they can be kept in cold storage, at a temperature of between 5º and 7º C, in a 3% brine solution.

Before shipment, the olives are washed repeatedly, sorted and packed in suitable containers in 5º or 6ºB brine.


Semi-ripe olives


These are obtained from olives that are picked when their colour is starting to change. They are harvested before complete maturity, when the flesh is quite firm and the oil is not completely formed. The process of darkening this fruit is typical in California where olives suitable for processing as green olives are selected as they enter the factory. They are placed in brine solutions of between 2.5 and 10%, in inverse relationship to fruit size, and are protected from the air.


How are they processed?

The olives are firstly placed in large concrete tanks in a 2% lye solution. When being prepared for the market, they are placed in containers with a low lye concentration, and rinsed with water and compressed air.

Repeated treatments with diluted lyes, each followed by aeration, facilitate penetration to the stone. Next, the olives are washed to eliminate lye residue and to reduce the pH level to close to neutral. 0.1% ferrous gluconate solutions are often applied to further darken the fruit. After again putting the olives in brine for several days, they are ready to be packed in internally-varnished cans. It is usual to sterilise these by heat treatment, controlling the temperature and pressure, in order to ensure preservation.


Ripe olives


These are olives that are harvested when the fruit is close to being fully ripe, once it has attained the colour and oil content corresponding to each particular variety

There are numerous preparations, using all types of olives, according to local tastes. Those in greatest commercial use are outlined below.


Black olives in brine

These are typical in eastern Mediterranean countries. In Greece they use the Conservolea variety, with some 200 olives per kilo. In Turkey they use the Gemlik variety. The fruits are handpicked when they are black, but before they are overripe and shrivelled from frost. They have to be transported as quickly as possible to the processing plant where they are sorted, washed and immersed in a brine solution at a concentration of 8-10%.

Large-scale plants use big 10-20 tonne vats, whilst small scale processors still use wooden vats. At the start of fermentation, the olives must be kept from contact with air, so the vats are covered and made airtight. The brine stimulates the microbial fermentation activity and reduces the bitterness of the oleuropein. The brine concentration drops to 6%, so it is necessary to increment it to 8% or even 10%. This is done by mixing the solution with the olives by means of a pump, which improves circulation. When the bitterness has been sufficiently weakened -this varies widely- the fruit can be sold. The colour fades during the process and can be corrected by aerating the olives for two or three days, although sometimes they are treated with 0.1% ferrous gluconate to make them darker. Finally, the olives are selected and packed in internally-varnished barrels or cans which are filled with fresh brine at 8%. They are popular on the market due to their slightly bitter taste and aroma.

These are also packed in vinegar (25% of the volume of the brine) and even undergo heat treatment; a few grams of oil are then added to each can to form a surface layer. This type of preparation is used for the Greek Kalamata variety. These are elongated, medium-sized olives which are slit laterally before being put into cans.


Black olives in dry salt

Also of Greek origin, these are prepared using overripe olives of the Megaritiki variety. They are vigorously washed and placed in baskets with alternating layers of dry salt equivalent to 15% of the weight of the olives. The result is an olive that is salty, not very bitter, that looks like a raisin and is for local consumption.

Finally, a mention should also be given to the numerous styles of table olive preparations in the different olive-growing regions. Some examples are olives treated solely with water to sweeten them prior to crushing or splitting, which facilitates washing. In many cases, before being eaten the olives are seasoned with herbs, pieces of orange, lemon, garlic, paprika, oregano, etc. Until the turn of this century, the table olive market was local, but since then it has expanded to non-producing areas where table olives have become popular. This is particularly true of the Spanish, Greek and Californian types.




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