Olive History - University of Georgia
The olive, Olea europaea L., is in the title genus of the Oleaceae family. The family contains about 22 genera and 500 species, most of which are placed in the Oleoideae subfamily with olive. Olive is by far the most economically important member of the family, but several others are important ornamentals: Fraxinus (Ash), Syringa (Lilac), Ligustrum (Privet), Jasminum (Jasmine), Forsythia, Osmanthus (Fragrant olive), and Chionanthus (Fringe tree). The genus Olea contains about 20 species.
Each Mediterranean country has its own unique cultivars, and many seedling trees are cultivated. The recently published world catalog of olive varieties lists over 130 cultivars, with more than 30 cultivated in both Spain and Italy. Some orchards (groves) are hundreds of years old, making it difficult to tell what cultivars were originally planted. Different cultivars are generally used for oil (e.g., 'Picual', ‘Leccino', 'Frantoio') and table olives ('Manzanillo', 'Sevillano', 'Ascolano', 'Calamata').
In California, 'Manzanillo' (Manzanilla) and 'Sevillano' (Queen) constitute about 90% of olive production, with small amounts of 'Mission', 'Ascolano', and others. ‘Manzanillo' is by far the major cultivar, having a small fruit that lends itself to the black ripe market, but with high enough oil content (>20%) that culls can be used for making olive oil. ‘Sevillano' is 2-3 times the size of ‘Manzanillo, but has low oil content and is used only as a table olive. Both were introduced from Spain in the late 1800s. ‘Mission' was formerly the most popular cultivar in California, but small fruit size, a relatively large stone, and susceptibility to diseases and late frost led to its decline in popularity.
ORIGIN, HISTORY OF CULTIVATION
The olive originated in the eastern Mediterranean area, and has been cultivated by man since ancient times. Trees are extremely long-lived (up to 1000 yr) and tolerant of drought, salinity and almost total neglect, and so have been reliable producers of food and oil for thousands of years. Earliest references of olive oil use and international trade date to 2000-3000 BC. Oil was used for cooking as well as burning in lamps. Several references are made to olive oil lamps in the Bible and other ancient writings from Greece and Rome. The olive was spread throughout Mediterranean Europe and North Africa very early, due to its ease of vegetative propagation and cultivation in dry climates. The Romans built on earlier work on olive culture by Greeks, Arabs, and Egyptians, and refined olive oil extraction and improved cultivars used for oil. Today, the industry remains largely confined to Mediterranean countries of Europe, the middle east, and north Africa, where it began thousands of years ago.
Olives were brought to California shortly after 1769, when the first mission was founded by Franciscan padres in San Diego. The California industry began in the late 1800s as settlers planted orchards from cuttings taken from the original mission trees. By 1900, there were about ½ million trees being grown in California, largely for olive oil production. Around this time, pickling and canning procedures were developed for producing black olives, which are the primary olive product from California today. Although there is some interest in producing high quality virgin oils in California, olive oil is largely a secondary outlet for table olives unsuitable for market.
In Mediterranean or desert climates, olives are frequently used as yard trees. They have attractive, silver-green foliage, full canopies, are evergreen, and require very little water and maintenance. However, the fruits will stain sidewalks and cars (black-purple, oily stains), and the pollen is highly allergenic. Substitute cultivars that do not fruit (e.g., ‘Swan Hill', ‘Majestic Beauty', ‘Little Ollie') have been developed for landscape use.
FOLKLORE, MEDICINAL PROPERTIES, NON-FOOD USAGE
Olives were cultivated in ancient times for lamp fuel, lubrication, and dietary fat, as there were few substitutes at the time. The olive is often mentioned in mythology and the Bible. Athene, the goddess for which Athens was named, is said to have won this right by placing the world's first olive tree on the Acropolis in Athens. The olive is associated with peace and security, probably from the passage in Genesis (8:11) where the dove (another peace symbol) returns to Noah's ark with an olive branch in its beak when God had made peace with man and stopped the flood. In contrast, olives were sometimes items of aggression; Odysseus jabbed an olive branch into the Cyclops' eye to blind him and thus escape being eaten. Olive crowns were awarded to brave Roman soldiers, and olive oil was awarded to the winner in ancient athletic competition.
Olive oil is an important component of the Mediterranean diet, and in fact is included in the European food pyramid. Those eating the Mediterranean diet (rich in olive oil, fruits, vegetables, and fish) are known to have lower rates of colon, breast, and skin cancer, and coronary heart disease. The active principals in olive oil are thought to be monounsaturated fats (primarily oleic acid), squalene, and phenolic compounds that function as antioxidants in the body. Oleuropein, responsible for the bitterness of raw olives, is one of the phenolics. Other simple phenols (e.g., tyrosol) and lignans (pinoresinol) also function as antioxidants. Extra virgin oils are higher in these protective compounds that processed oils. Olive oil may act by reducing the LDL ("bad") and raising the HDL ("good") forms of cholesterol in the blood. Olive extracts have been shown to have hypoglycemic activity, and oil reduces gallstone formation by activating the secretion of bile from the pancreas. Olive oil may act as a mild laxative.
World (FAO 2002) - 15,724,187 MT or 35 billion pounds. Olives are produced in 39 countries worldwide on an area of over 20 million acres. Olive is the most extensively cultivated temperate fruit crop in the world, since its acreage has surpassed that of grape several years ago. Production has increased 44% since 1992. Average yields are 1680 lbs/acre, but range widely from 300 to over 8500. Olive oil is produced in 29 countries worldwide, and the leading producers of oil are the same as those for overall olive production. Olive oil production was 2.4 million MT in 2002. Over 75% of the world's olive oil is produced in just 3 countries - Spain, Italy, and Greece. The vast majority of the olive crop is used for oil.
Top 10 Countries
(% of world production)
1. Spain (27%)
2. Italy (20%)
3. Greece (16%)
4. Turkey (11%)
5. Syria (6%)
6. Tunisia (3%)
7. Morocco (3%)
8. Egypt (2%)
9. Algeria (2%)
10. Portugal (2%)
United States (USDA 2002) - 90,000 MT or 198 million pounds, produced on 36,000 acres, or <1% of world production. All production is in California, largely in the central valley. The industry value was $60.7 million in 2002, and has varied between $34 and $102 million over the last decade. Prices were about 30¢/lb in 2002, higher than average for the last decade. Average yields are 5700 lbs/acre, about three-fold greater than the worldwide average yield. Imports of table olives in brine were 101,321 MT in 2001, up from about 60,000 MT in 1992. Thus, the USA imports more table olives than it produces annually. Olive oil imports were 217,664 MT (68 million gallons), almost double that of a decade ago. Dried olives are also imported, but in tiny quantities by comparison (only 367 MT).
Olives are large, evergreen shrubs in their native state, but are trained as stout trees on massive trunks, especially in older plantings. Most trees have round, spreading crowns, but tall, cylindrical trees are grown in some parts of Europe. Trees in neglected groves grow almost imperceptibly slow, whereas irrigated trees in California may reach 12' in 4 years. Olives have the longest-lived trees of any fruit crop; some trees in Europe are claimed to be 1000 years old.
Leaves are small (1.5" long, 1/4-1/2" wide), linear, with entire margins and acute tips, silver-green in color, and fairly thick. Leaf arrangement is opposite, as for all members of the Oleaceae. Leaves live about 2 years. Olives are some of the longest lived trees in the world.
Small, off-white flowers are borne in racemose panicles of 15-30 flowers in axils of 1 year old wood. Most flowers are staminate by pistil abortion, leaving only 1-2 perfect flowers per inflorescence, which may set fruit. The ovary is superior, and there are 4 sepals and petals, and 2 stamens. Flowering occurs rather late relative to other tree crops, May in California.
Most olives are self-fruitful, but some cultivars bear heavier crops when cross-pollinated. Wind is the pollinator.
The fruit type is a drupe. Fruit are oblong with smooth, waxy surfaces. Color is green when immature, turning yellow-green in autumn, with red, purple, or black coloration at full maturity. Dark coloration results from anthocyanin production in the exocarp and mesocarp. A stony pit surrounds a single seed. Olives require 6-8 months for full maturation, but table olives are harvested earlier when firm, and oil olives are left on trees until oil content reaches 20-30% (early winter). Olive fruit are drupes, green when immature and turning purple or black when fully mature. Table olives are harvested when pale green or turning yellow, and oil olives are harvested later when fully ripe.
Trees produced vegetatively may flower in 2-3 years, produce significant crops in 4 years, and reach full production in about 7-8 years. Seedling trees have a long juvenile period, and take up to 10 years to reach full cropping. Olives have a tendency toward heavy alternate bearing unless they are pruned annually and thinned in the "on" year. Olives can be thinned chemically with NAA applied at about 150 ppm 2 weeks after full bloom. However, chemical thinning requires great managerial skill, is cultivar-dependent, and subject to erratic response due to weather conditions.
Soils and Climate
Olives are grown on a wide variety of soils, many too poor to support cultivation of other crops. They are tolerant of high pH, salinity, excess boron, and drought, but will die in a few weeks if flooded.
Olives are supremely adapted to Mediterranean climates, and cannot tolerate high humidity due to disease and physiological disorders. Fluctuations in humidity and temperature 1-3 months following fruit set cause a condition known as aseptic apical decay on fruits. Part of the fruit surface turns black, and the fruit usually abscises; even in Mediterranean climates, losses may reach 30%.
Chilling requirement varies among cultivars; those grown in California have relatively high requirements (1000 hr). Cultivars grown in northern Africa fruit well with only a few hundred hours of chilling. Some texts erroneously refer to the chilling requirement as "vernalization", since flowers develop during or following (as opposed to before) the cold period. However, floral induction is known to occur in November prior to flowering, so olives are chilled, not vernalized. Cold hardiness may approach 5-15°F in midwinter when fully acclimated, but foliage and fruit are damaged by frost during active growth.
The ease of vegetative propagation of the olive undoubtedly contributed to its early domestication and use by man. Worldwide, rooting of cuttings is the most popular method of olive propagation. Unusually large cuttings will root: in Spain, cuttings with diameters up to 6-12" are used to establish new plantings. They are pruned heavily and mounded with soil throughout winter, and rooting takes place prior to summer heat. More commonly, hardwood cuttings are made from 3-4 year-old wood taken in mid-winter. Leaves are striped off completely, and cuttings are rooted over the course a several months. Bottom heat and growth regulator dips improve rooting.
Softwood cuttings, or leafy stem cuttings root better and are more common than hardwood cuttings. Leafy shoots are taken from 1 to 2-yr-old wood in summer, treated with growth regulators, and stuck in well aerated media under mist for 2-3 months. A 4-5" cutting will attain a height of about 2' by the following summer and be ready to plant. Planting is often delayed until the following spring due to the hot, arid conditions of summer, and consequent poorer field survival.
Grafting and Budding
T-budding and wedge grafting are used for cultivars which root poorly or when rootstock use is warranted. T-budding is done in spring when bark is slipping on rootstocks propagated the previous year from seed or cuttings. Simple wedge or V-grafts can be made in winter or spring. Scions 2-3" long, taken from the central portion of 1-yr shoots, are grafted onto stocks.
Suckers and Ovuli.
Suckers are simply shoots that arise from the trunk or roots, and thus are similar to a naturally rooted cutting. They can be removed and planted directly if well-rooted, or treated as a softwood cutting if the root system is poor. Ovuli are masses of callus tissue that often form at the base of trunks of older trees. They produce shoots, and if mounded with soil, adventitious roots. Both are primitive methods of propagation, practiced mostly in less intensive areas.
Due to the ease of rooting, most olives are grown on their own roots, from cuttings, suckers, or ovuli. There are no particular rootstocks of worldwide importance. Cultivars that germinate well from seed, or are easily rooted are generally used as rootstocks. The cultivar 'Oblonga' is resistant to Verticillium wilt and is used in the landscape, but rarely used commercially. Rootstocks are known to affect olive yield, tree size, and fruit quality, but the effects are highly cultivar dependent. The potential for dwarfing olive by using rootstocks appears to be possible, but as yet unexploited.
Planting Design, Training, Pruning
Traditional olive groves are usually comprised of large trees, scattered at irregular distances from each other, as a result of tree mortality or grafting/rooting in-situ to fill in empty spots. There may be as few as 10 trees/acre, and usually no more than 40 trees/acre. Many are situated on steep hillsides or terraces which are unsuitable for other crops. As little as 10-15% of the land area is covered by tree canopy. Since most groves are not irrigated, wide spacing is necessary for production since trees must survive on stored soil water throughout the summer. When possible, the soil surface is cultivated to eliminate weeds. Intensive orchards are typically planted at densities of 30-40' apart in all directions, for about 40-60 trees/acre. Filler trees may be used, which initially double the tree density, removing them after 8-10 years. Super high density orchards, with hundreds of trees per acre are used to a limited extent.
Olives naturally form large shrubs, with spreading canopies similar to citrus trees. Traditionally, trees were trained to single trunks devoid of scaffolds over the lower 6 ft. This allowed grazing of animals in groves, intercropping, and ease of movement around trees by cultivation equipment and harvesting labor. Initial productivity was sacrificed by heavy pruning of young trees to form single trunks. In more intensive plantings, trees are pruned very little during the first 3 years. The objective is to develop an open canopy composed of several scaffold limbs. Young trees may be headed to promote initial branching, and shoots below 2.5 to 3' removed to allow shaker attachment for mechanical harvest. Afterwards, undesirable limbs are thinned and suckers removed from the trunk, and trees branch naturally on their own. Mature trees that are mechanically harvested are trained to fewer than 5 scaffolds to speed the harvest operation because mature trees require individual limbs to be shaken, not trunks.
Pruning is necessary to stimulate new fruiting wood for the following year's crop, decrease the tendency for alternate bearing, and help control insect and disease problems. In old, traditional groves, olive trees are sometimes burned down or severely cut back and allowed to regrow on an infrequent basis. This eliminates production for some time, but accomplishes the task of rejuvenating the trees. It is far more desirable to prune annually, but labor availability and tradition may preclude annual pruning.
Olives tend to form thick canopies of tightly bunched shoots, which limits productivity and encourages pests. Pruning cuts are designed to open the canopies to light, increasing the depth of canopy involved in fruiting and discouraging black scale infestation since these insects congregate in shaded areas. Spray penetration is also enhanced on trees with open canopies. Thinning cuts are made in dense areas, removing shoots growing downward, and long, willowy shoots that do not lend themselves to shake harvest. Time of pruning is critical; the bacterium causing olive knot disease is spread by rain and can only enter trees through wounds. Thus, unlike most fruit trees, olives are pruned in spring or summer when rain does not occur to minimize this disease. Also, pruning harder in "on" years and lighter in "off" years helps decrease the degree of alternate bearing.
HARVEST, POSTHARVEST HANDLING
Most table olives are harvested when they change from green to yellowish-green in color and are firm; this is usually mid-autumn. The mesocarp exudes a white juice when squeezed at this stage. In California, most fruit is processed into "black ripe" olives, so some red coloration is allowable at harvest. Greek-style table olives are harvested at a more mature stage, when dark red to black. Oil olives are harvested in late autumn or winter when they have turned black and reach their maximum oil content (20-30%). Delaying harvest results in poor quality oil due to loss of essential oils and aromas and increases in acidity. Delaying harvest also results in increased alternate bearing, and trees used for table olives often fluctuate in yield less than trees used for oil.
Olives are traditionally hand harvested, a process that is not only tedious and laborious, but represents the major proportion of the costs of production. Hand harvest is accomplished by three techniques: 1) collection of fallen fruit from the ground, 2) "milking", or the stripping of fruit with half open hands from limbs which falls into picking bags or onto nets below the tree, 3) beating limbs with large sticks to dislodge fruit, which is also collected on nets. Some table olives and high quality oil olives are picked individually into baskets around the picker's neck to avoid damage and subsequent quality loss. Collecting fruit which fall naturally to the ground is inexpensive, but seriously compromises oil quality. Thus, milking or beating are most commonly used.
Mechanical harvest of olives has been studied and attempted in various forms for years. It is used to a limited extent in more intensive orchards. Compared to other tree fruits that are mechanically harvested, olives are problematic. Olives require about 5 times more shaking energy than other fruits such as prunes and almonds, due to the willowy nature of the tree and the resistance to detachment of fruit. Using mechanical shakers designed for almonds in California, at best 65-80% of the fruit can be removed from the tree. The remaining fruit are either lost or must be hand harvested. Cullage can be 4 times higher with mechanical shakers. Initial costs of equipment are also high, precluding this approach for small growers.
Table olives are cleaned and transported to processing plants, where growers are paid based on fruit size, color, and total weight. The fruit are washed and may be stored temporarily before processing (see below). Raw olives are bitter due to the glucoside oleuropein in fruit, which is neutralized by soaking in 1-2% lye (sodium hydroxide) followed by thorough leaching with water to remove the lye. Black table olives are those exposed to air during this process, which allows the oxidation of phenolic compounds, yielding a black color. Green table olives are exposed to lye in the absence of aeration, and remain green. Spanish green olives are fermented in brine to which lactic acid bacteria have been added after lye is leached. A hot brine solution is added to fruit in cans or jars, and is heated to 240°F for 1 hr for pasteurization. Many canned olives are pitted prior to canning, and green olives often have pimentos (small slices of peppers) placed into pit cavities.
Oil olives are brought to mills where they are crushed whole, usually by two large, round stones rotating in opposite directions. The resulting paste is spread onto round mats of coconut fiber or nylon mesh with holes in the center. The mats are stacked onto a dowel under a hydraulic press, and the liquid (water and oil) is pressed out in a process known as "cold pressing". Alternatively, olive paste can be centrifuged to extract oil. Percolation is a process used to extract oil by submerging a metal plate in olive paste, to which oil will adhere; the plate is removed and oil drips or "percolates" from the plate into a vessel. Cold pressing is the most popular method of oil extraction. Finally, the water is separated from the expressed oil by centrifugation, and the final oil may be filtered for clarity.
Table olives are often stored in brine or acetic/lactic acid solutions prior to processing since pickling vats can process only so many tons of olives at one time. Olives can be stored for several weeks or months in brine or acid solution. Alternatively, green olives can be stored in refrigeration for 4-8 weeks, depending on temperature, before they experience chilling injury. Temperatures of 40-50°F are used. Once processed, table olives can be stored for about 2 years without loss of quality, similar to other pickled products. Olive oil can be stored many months, particularly if kept from light and heat. It may go rancid, like other vegetable oils, when exposed to oxygen.
CONTRIBUTION TO DIET
Worldwide, most olives are made into olive oil, with smaller amounts canned in a number of different styles. California production is somewhat anomalous in that the vast majority is a single product, the black-ripe canned olive.
Olive oil marketing is controlled by an international agreement, overseen by the International Olive Oil Council located in Madrid. Flavor and acidity are the primary determinants of oil quality. Official definitions of olive oil are based upon flavor, acidity, and processing methods used.
Virgin oil. This is minimally processed oil extracted by cold pressing. It has three subcategories: extra, fine, and ordinary, based largely on acidity and flavor. Extra virgin olive oil has less than 0.8% acidity (by weight from oleic acid), excellent flavor, and often comes from the first pressing of olives. Fine oil is often just termed "virgin" and has acidity of <2%. Ordinary virgin oil has acidity of up to 3.3%. Virgin oils with acidity greater than 3.3% are not used for human consumption, and are designated "lampante" meaning lamp oil.
Refined oil. This is virgin olive oil refined to remove off flavors and odors by lye or other treatments, which do not alter the glyceridic structure of the oil. It has acidity of < 0.3%.
Blended oil. This is virgin oil blended with refined oil with acidity <1%. It is labeled "pure", and constitutes the bulk of olive oil sold.
Olive-pomace oil or residue oil. Oil recovered from pressed olive paste by solvents falls into this category. It cannot be submitted to re-esterification processes or mixed with other plant oils. Olive-pomace oils are classified as "crude" or "refined", with the latter having lower acidity than the former. A third category, simply "Olive pomace oil", is a blend of refined pomace oil and virgin olive oil with acidity <1%.
Per capita consumption of olive oil varies widely by country. In Greece, over 17 liters (4.5 gallons) are consumed per person, the highest per capita rate in the world. Italians and Spaniards consume about 10 liters (2.5 gallons), but most other countries consume less than ½ a liter (1 pint) per year. Canned olive consumption is far lower, but has also increased over time. Consumption of canned olives was about 0.7 lbs/person in 1990.
REFERENCES AND FURTHER READING
Bartolini, G. And R. Petrucelli. 2002. Classification, origin, diffusion and history of the olive. FAO, Rome.
Dolamore, A. 1994. The essential olive oil companion. Interlink Books, New York.
Ferguson, L., G.S. Sibbett, and G.C. Martin (eds). 1994. Olive production manual. Univ. Calif. Div. Agric. Nat. Res., Oakland, Ca. Publ. 3353. 160 pages.
Katsoyannos, P. 1992. Olive pests and their control in the Near East. FAO Plant Prod. & Protect. Paper 115.
Knickerbocker, P. 1997. Olive oil: from tree to table. Chronicle books, San Francisco.
Lavee, S. 1985. Olea europea, pp. 423-434. In: A.H. Halevy (ed). CRC handbook of flowering, volume 3. CRC Press, Boca Raton, Fla.
Martinez-Moreno, J.M. 1975. Manual of olive oil technology. FAO, Rome.
Pansiot, F.P. 1961. Improvement in olive cultivation. FAO Agric. Studies No. 50.
Taylor, J.M. 2000. The olive in California. Ten Speed Press, Berkeley, CA.
Tellez Molina, R. (ed). 1977. Modern olive production. FAO, Rome.
Zalom, F.G., R.A. Van Steenwyk, and H.J. Burrack. 2003. Olive fruit fly. Univ. Calif. Statewide IPM Program, Pest Notes Publ. 74112.