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.
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
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
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
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
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.
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.
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
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
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
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.
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
SKIN: The skin of the fruit should be fine, yet elastic
and resistant to blows and to the action of alkalis and brine.
CONTENT: A high sugar content in the flesh is an asset. The lowest
acceptable level is 4%, especially in olives that undergo
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 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
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 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
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.
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.
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,
The most commonly used varieties are Manzanillo, Gordal and Moroccan
Olives belonging to the Picholine variety from Languedoc and Lucques in
southern France are prepared in this manner, as are other varieties from Morocco
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.
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
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.
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%.
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
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