PLANT OF THE WEEK

Dr. T. Ombrello - UCC Biology Department

THE OLIVE

Common name:            Olive

Scientific  name:          Olea europaea

Explanation of scientific name:       

Olea           - the classical Latin name for this tree

europaea  - of Europe

The value of the olive tree has been recognized since ancient times.  For thousands of years its fruits have been utilized for food and as a source of an oil that is not only edible but has been used in lamps, religious ceremonies, medicine, cosmetics, and a variety of industrial applications.

Mankind’s fascination with this species is evidenced by its appearance in writings and archaeological excavations.  Exactly when it was first cultivated is unknown, but olive pits have been found at several archaeological sites north of the Dead Sea in Israel dating to 3700 BC.  Archaeologists have also identified its use on Crete since 3000 BC, and the Egyptians are known to have cultivated the tree in the seventeenth century BC.

Historically, the olive has been recognized as a symbol of peace and the beginning of new life and hope, as expressed in the biblical story of the flood.

                        “And the dove came back to him in the evening and lo, in her mouth a freshly plucked olive leaf; so Noah knew that the waters had subsided from the earth.”  (Genesis 8:11)

The olive tree was so highly regarded that in the Bible’s parable of the trees, the other trees of the world appealed to it to reign over them.

                        “The trees once went forth to anoint a king over them; and they said to the olive tree, ‘Reign over us’.  But the olive tree said to them, ‘Shall I leave my fatness, by which gods and men are honoured, and go to sway over the trees?’”  (Judges 9:8-9)

Homer, Herodotus and Virgil all wrote about the olive, and Plato, Aristotle, Phidias, Praxiteles, Scipio of Africa, Caesar, Christ and the Apostles all flavored their food with olive oil.

In Greece the olive tree was sacred to the goddess Athena and she presented olive branches to the winners of contests for the city of Athens.  Distinguished Greek citizens, and especially successful Olympic participants, were honored with crowns of olives.

In Roman times, kings were anointed with olive oil.  Olive wood could only be used for altars of the gods, and it was forbidden to burn olive wood for “profane” purposes.  A Roman holding out an olive branch was making overtures for peace.

The olive tree is the only member of the olive family of plants (Oleaceae) that is used for food.  The family, however, encompasses a number of species with which most people are familiar.  For example, lilac, forsythia, jasmine, osmanthus, ash and privet are all close olive relatives.

Native to the Mediterranean region, the cultivated olive is a small tree (to 25 feet in height) with narrow, silver-gray colored leaves 1 – 3 inches in length.  The tree’s small white flowers are fragrant, and develop into ½ - 1 ½ inch long green fruits that eventually turn a shiny black color when ripe.  It is a long-lived tree, producing a gnarled, irregular trunk with old age.  These aged trunks are often hollow as a result of internal decay, but they still are quite productive.  Some olive groves in Israel are probably more than 1000 years old.

The wild form of olive (Olea europaea oleaster) is believed to be the ancient ancestor of the cultivated type.  It is a bush with 4-sided thorny branches, broad leaves, and small fruits.

The olive has specific habitat requirements that must be met in order for it to thrive.  It does best on a sunny, arid site with well-drained soil and a long, hot growing season.  While temperatures below 12^oF will kill the tree, it does need some winter chilling.  A winter of 12 – 15 weeks with daily temperatures ranging from 35^oF to 60^oF fulfills its needs.  Under these conditions olives will begin production even when only several years old.  An olive grove in its prime will yield 1 – 5 tons of fruit per acre each year.  Most olive production (95%) is centered around the Mediterranean region, with Italy and Spain being the leading producers.  But olives are also grown in South Africa, Argentina, Chile, Peru, Mexico, California, Australia, and China.

The olive trees that produce fruit for direct consumption are not the same as those used for producing oil.  Those varieties grown specifically to produce “table olives” have larger fruits and firmer flesh than others.  They are picked either when they are fully ripened on the tree in the Fall (black olives), or when they are fully-grown but still green.  Freshly harvested olives are quite bitter, due to the presence of a glucoside.  The bitter flavor is partially neutralized by washing or soaking the fruits in water or in brine.  The bitterness is more completely removed by the use of a lye solution followed by a rinse in water.  The olives are then usually packed in brine or occasionally oil.  Stuffed olives are pickled green olives with the pit removed and replaced by a piece of pimento or sweet red pepper.

The extensive use of olive oil in foods is relatively new (since the 17^th century) in comparison to the fruit’s used for other purposes.  It is interesting to note that it is the only edible oil made from fruit instead of nuts or seeds.  Not counting the pit, the fruit is 20 – 30% oil.  The olive tree varieties selected for oil production must have their fruits harvested just before they are fully matured.  If the fruits are left until they mature to the point of falling from the trees, the oil produced is of inferior quality.  Historically the fruits have been thrashed from the trees, and more recently shaken from the trees by large mechanical harvesters.  Both practices result in damage to the tree, so today the most accepted method is to literally comb the fruits out of the tree into cloth or nets placed on the ground.  After harvesting, the fruits are cleaned and crushed in special oil mills (traditionally granite millstones) until reduced to an oily paste.  The paste is placed into woven mats of rush, grass or hemp and then subjected to pressing.  The mats retain the pits and pulp.  The collected fluid is centrifuged to yield the golden or greenish-golden oil.

The first pressing yields the finest oil, that can be bottled directly with no further treatment.  It is referred to as “virgin” oil.  What most people do not know, however, is that there are numerous grades of “virgin” olive oil, classified on the basis of percent acidity expressed in oleic acid.  The acidity range is from 1% – 4%. 

Extra virgin is the finest quality with a mild, delicate odor and flavor with no “bite”.  Italians describe this high quality as “ardente” (the ardent or passion of the virgin).  Oils without the virginity label, sold variously as “pure olive oil”, “olive oil” or “husk and olive oil”, are the result of second and third pressings or even chemical extraction.  Chemical extraction is used because no amount of pressing can remove more than 25% of the oil from the paste.  While the non-virgin oils may have a nutritive value equal to virgin oil, the quality is just not there.  To the olive oil connoisseur, these inferior quality oils are referred to as “lampante”, meaning suitable for an oil lamp but not for food.  These low quality oils are used for a number of other purposes, including wool combing in the textile industry, cosmetics, medicines, soaps and lubricants.  Olive oil has properties that make it different from most other oils.  It solidifies at 32^oF and spoils (becomes rancid) readily if stored in an area exposed to light.

The use of olive oil in foods in the United States is becoming more popular.  It has long been popular in other countries.  The per capita consumption of olive oil in Italy is 10 liters per year.  Prized for its rich flavor, purity, and lack of greasiness, olive oil is resistant to chemical alteration at high temperatures, and, therefore, is excellent for cooking.  Research has shown that it is among the most digestible of oils and there is an increasing body of evidence suggesting that its use reduces the incidence of coronary heart disease.