According to the Food and Agriculture Organization, olives are the most extensively cultivated temperate fruit crop in the world; the area of olive groves exceeds that of vineyards. Around 90% of the harvest is destined for oil, with Spain, Italy, and Greece between them responsible for over 75% of world production and Syria, Turkey, and Tunisia contributing an additional 15%. Newer producers such as California, Australia, and Argentina are virtually insignificant on a global scale. World production of olive oil has expanded by about 60% over the ten years to 2004, with consumption increasing at approximately the same rate.
Andalusia in Spain is the principal olive oil-producing region in the world. Numerous varieties of the olive tree are used, but one, Picual, is by far the leader (although this fact can be obscured by the use of different names for it in some parts of the region), and accounts by itself for something like half of Spanish olive production. It takes its main name from the shape of the fruits, which have a somewhat pointed tip (pico in Spanish). The chemical composition of its oil is admirably balanced. Of the other leading varieties for oil, Hojiblanca takes its name from the whitish underside of its leaves; and is used to some extent as a table olive. Lechin de Sevilla is grown mainly in the province of Seville. Picudo, another olive with a pointy tip, yields a delicate oil with flowery and fruity attributes, unmatched for certain purposes (gazpacho, warm salads, cake-making, etc.), and has excellent aroma and flavour.
The other main producing countries have their own favourite varieties, attuned to local conditions; Koroneiko, for example, is the major one in Greece. The olive oil of Nyons in S. France, which was the first to be awarded AOC (Appellation d'Origine Contrôlée) recognition, is made from the Tanche variety. In Italy, Leccino and Frantoio are relatively common, though a range of cultivars contributes to the distinctive qualities of oil from each region. In California the Mission variety (as it is now called), was established at Spanish missions in California before 1800; it is popular both for table olives and for oil.
The olive fruit, a drupe with fleshy pulp and a high fat content (12–35%, depending on variety and degree of ripeness), contains a glucoside which makes olives, especially unripe ones, very bitter. This has to be removed from table olives in the first stage of the preserving process, but it separates naturally from the oil when olives are pressed to produce olive oil.
Olives for oil must be gathered quite ripe. In the Mediterranean the harvest comes in late autumn and winter: in Provence, for example, it begins around 15 November, well after the grape harvest. Traditional harvesting methods of hand-picking and beating still compete with mechanical tree-shakers; mechanical harvesting is more common in newer olive-growing countries. The fruit must be gathered undamaged and crushed with a minimum delay to avoid oxidation and loss of quality.
Traditional practice is to clean the olives, removing stems, twigs, and leaves, then to crush the fruit without breaking the stones, spread the resultant paste on fibrous mats, stack these on top of one another, and press. The fluid that is extracted, when allowed to settle, separates into oil and a bitter watery substance, amurca to Romans, which found numerous uses on old-fashioned olive farms.
Stone crushing mills, trapeti, powerful enough to crush the flesh effectively but sufficiently accurate in gauge not to break the olive stones, are among the most impressive examples of 2,200-year-old Roman farm technology—and some such mills are still used.
Stone mills, however, are very labour intensive and considerable care is necessary at all stages of the process. It is difficult to keep the mats (once made of esparto grass) scrupulously clean, a necessary step to avoid the possibility of off flavours. Nevertheless, this practice yields the highest percentage of oil, and traditionalists believe oil produced by this method to be the highest quality.
The modern alternative is continuous extraction, which involves the same basic steps of milling, mixing, and separating the oil from the solids but using centrifuge technology instead of pressing. A hammer mill crushes the olives to a paste which undergoes malaxation, a process of slowly mixing, usually at a slightly higher temperature (no more than 28 °C), in order to free the oil for easy extraction. Centrifugal decanters then separate the oil from the fruit/water residue (the pomace). The new oil is allowed to settle for a few months before bottling. This continuous process produces oils with different flavour characteristics; they might be more bitter and pungent because of a higher content of phenols, tocopherols, and other aroma components. On the other hand, they are more resistant to oxidation.
It is not necessary to filter olive oil before bottling, and unfiltered oil has more and better flavour than filtered oil. But it is turbid and has vegetable residue. This fondo is characteristic of the best oil and is quite harmless. It can easily be used up just by shaking the bottle a little when using the oil.
The pomace or residue left after the first, cold pressing is a dryish pulp which can subsequently be treated with heat and water or solvents to extract oil of a much lower quality which can then be blended with virgin oils to produce commercial brands which have little (if any) flavour but do have a uniform quality which, together with a lower price, is attractive to many consumers.
Olive oil is variously classified for marketing. The International Olive Oil Council, with headquarters in Madrid, has ruled that ‘Virgin’ olive oil is ‘obtained from the fruit of the olive tree solely by mechanical or other physical means, under conditions, particularly thermal conditions, that do not lead to alterations in the oil, and which has not undergone any treatment other than washing, decantation, centrifugation and filtration’. The corresponding US regulation, of 1982, defines ‘Virgin’ oil as ‘resulting from the first pressing of the olives and … suitable for human consumption without further processing’.
For European olive oils the additional classification ‘Extra Virgin’ simply indicates a low acidity, expressed as oleic acid (less than 1%), a feature which is usually desirable for flavour.
Olive oils vary in flavour according to the varieties from which they are extracted, the degree of ripeness when they are picked, and, like wine, from season to season. In general, early-picked fruit yields a more pungent and peppery oil, a result of the relatively high levels of polyphenols. As the fruit matures the concentration of polyphenols rapidly decreases, and riper olives give mellow, soft, fruity oils. Varieties like Verdale produce soft fruity oils, while Frantoio yields oils that are bitter, pungent, and fragrant.
The uses of olive oil need no explanation. Most of it is used in cooking, where it is important both for its contribution to flavour and also for its nutritional properties. It is recommended for frying because of its high smoking point and because, unless overheated, it keeps its nutritional value better than other oils. To preserve these properties, olive oil should be stored away from light and excess heat.
Olive oil has one special virtue, unique among the commonly available fats and oils. It is a predominantly monounsaturated oil, containing around 75% monounsaturated fatty acids. As a plant product, it contains no cholesterol. Virgin olive oil contains high levels of antioxidants (phenols, vitamin E), and it therefore has a beneficial effect on blood pressure and on cardiovascular disease. A diet rich in olive oil is reported to be associated with a reduced risk of certain cancers. Indeed, olive oil is considered one of the main constituents of the ‘Mediterranean diet’ whose effects on health are so widely praised.
Andrew Dalby has written essays and books about food in classical times, especially Siren Feasts, on food and gastronomy in classical Greece.
Barbara Santich is responsible for the Graduate Program in Gastronomy at the University of Adelaide and the author of six books, including The Original Mediterranean Cuisine. Her research interests focus on France and Australia.
