Though it may seem surprising, it is not taken for granted that processing olives will always produce an oil of impeccable quality. Many factors contribute to determine the unique character of a freshly crushed olives: a torrential rain might irremediably spoil olives that only a few minutes before might have yielded a perfect product. Every grower/producer must do his utmost to get the best possible oil, watering the plants when necessary, protecting them from parasites, harvesting the olives in the best possible way and seeing that they are processed immediately thereafter.

The Classification of Olive Oils

The evaluation of the "quality" of an oil is done lot by lot, not on the output of the entire harvest. Usually the oil of a single lot is that of a single grower, or of one place of origin characterized by a particular cultivar. A sample is taken from every lot and submitted to the strictest tasting tests and chemical-physical analysis; only later will it be possible to assign it to one of the categories established by the European Community regulations. A sharp distinction is made between olive oils and pomace oils, because the two products are processed differently. After crushing the olives there remains a solid residue of pulp and pits, called pomace. The latter still contains a certain amount of oil which varies according to the processing system used. This oil is extracted with solvents, usually hexane, and with the same technology used for the production of seed oils.

Chart of the extraction process of different oils
The table shows by means of flow-charts the various phases of the extraction of an olive or a seed oil.

Among olive oils, any oil that has undergone no extraction processing other than the strictly physical-mechanical one, without using solvents or other chemical manipulation, and is not mixed with oils that are not from olives is designated "virgin olive oil".
The product from crushed olives is certainly "virgin"; but to be designated "extra virgin" it must prove to be totally free of defects under sensory analysis, and fully in accordance with the chemical-physical parameters established by international regulations.
The presence of a high level of free oleic acid is not perceptible to the palate, but is revealed by laboratory examination. The acidity to which the European Community regulations refer is a chemical parameter connected principally with the condition of the original raw material and with its processing. When olives have been processed under optimal conditions, the acidity is much lower than 0.8% (less than 0.3% in exceptional oils); but it can also reach 10% and more, when the harvesting has been carried out under poor climatic-technological conditions.
The "lampante virgin oils", so called because they were used in the past as lamp fuel, also contain many precious, natural components, beneficial for human diet and health (essential acids, vitamins, antioxidizing agents). These oils are refined to lower their free acid levels, and to remove unpleasant aroma and color characteristics without altering their chemical structure.

After refining an olive oil tastes like a practically faultless fatty substance. Before being sold to consumers it must be blended with extra virgin or virgin olive oil which contributes color and taste. The law does not set the minimum per cent of virgin or extra virgin oil to be added; usually the average amount is 5%-8%, but the best producers go as far as 30%, using only extra virgin oil, that makes their product much tastier to the palate as well as nutritionally perfect "Olio di Oliva".