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As well as culinary uses, olive oil was used to illuminate Mediterranean houses until the arrival of electricity, and lubricated the machines of the industrial revolution just as it served the Romans earlier as axle grease.
Although many countries now produce olive oil, the Mediterranean is still its true home. Italy, Greece and Spain (60% of world production) are the largest producers, and oils from each of these countries have their own characteristics. Even within each country, there is a huge diversity of regional flavours and styles, and more than 80 varieties of olives are used in the production of olive oil.
Olive oils are now rated on their acidity levels. The higher the acidity level the less aromatic the oil will be and usually the less expensive.
The best oil is produced by crushing the olives to a paste between two stone wheels. The crushed olives are laid out on mats, stacked and weighted to extract the oil. The slow pressing of the olives doesn"t build up heat and is referred to as "cold pressed". Generally the lower the heat, the lower the acidity - the oil retaining its full flavour.
The oil is then separated by the use of a centifuge. This first pressing yields what is called Extra Virgin Olive Oil with an acidity level of less than 1 per cent.
The second pressing of the same olives yields Fine Virgin Olive Oil or Virgin Olive Oil with acidity levels of between 1.5 and 3%.
Oil labelled "Pure Olive Oil" is a blend of refined olive oil with small amounts of extra virgin or virgin added to give character.
"Olive Pumace Oil" is the result of treating the remaining pulp with solvents to extract any additional oils. This is the least expensive of the olive oils.
The term "Light Olive Oil" is a reference to its colour and flavour not to its caloric content. All olive oil has basically the same amount of calories.
Extra Virgin and Fine Virgin oils might be filtered or unfiltered - the latter being slightly more robust and rustic in flavour than the filtered variety.
Experts judge oils rather like wine - by colour, bouquet and taste. All three qualities depend on the ripeness of the olives when they're harvested, how they are kept and how the oil is extracted. Unlike wine, olive oil is always better in the year of its production, and the colour - ranging from pale golden yellow to deep green - generally has no bearing on the taste. Tasters sample the oil in small-lidded cups, designed to hide the colour, so it doesn't influence their decision on its taste. The flavour is described by words such as bland, fruity, grassy, hay and peppery.