The classification of the different types of olive oil is determined by quality, which can be judged by whether an oil is taken from the first or second pressing of an olive crop, the type of olive (Kalamata, from that region of Greece, is the most common, but there are others) and the stage of the olive harvest ( early, middle or late ) when the olives were harvested. Quality is judged by a scientific scale, analyzing the level of acidity, oxidization, and the presence of other (organic) elements in the olive oil.

Measuring by expert tasting, we can describe their characteristics in terms of organaleptics, that is, by the senses, notably aroma and taste. In terms of quality, all olive oils, whether they are edible or not, if they are produced by a traditional olive mill, can be categorised by three levels of quality defined by the process, extra virgin or virgin, from a first pressing of the olives, and ordinary olive oil, from a second pressing of the olives, and after each has been filtered, stored and left to settle. The third category is oils refined by other, chemical, means from the residue of these processes.

The first pressing will produce what's known as extra virgin olive oil, of a grading below 1 per cent acidity, and virgin fine olive oil, whose grading does not rise above 2 per cent. These are considered the best olive oils for human consumption, according to legislation by the European Union. This clarification is achieved during either separation or settling.

The second pressing, of the same olives, produces ordinary virgin olive oil, whose acidity must not exceed 3.3 per cent in acidity. Any oils above this level of acidity are oils not fit for immediate consumption and which will need to be blended with virgin or extra virgin oil for consumption. The oil made in this pressing, when it is processed to separate the oil from the water content, is an oil that exceeds the 3.3 per cent limit, and is called in Spanish 'lampante', lamp or clear oil, the term deriving from its use in earlier times as a fuel for oil lamps. This oil and ordinary virgin olive oil are always refined further, and in the case of ordinary virgin oil can be used to improve other oils.

All the pressing processes produce a residue, known in Spanish as 'orujo', a liquid that is further subjected to a lengthy cleaning procedure, its oil extracted by means of solvents (hexane, trichloroethylene, carbon sulphur are the most frequent), alkaline neutralization, refining, desodorization, discolouring, and filtering to obtain the oil from the orujo, which is the only olive oil that is not obtained by pressing. This type of olive is used mainly in commercial deep frying, is very good at resisting high temperatures and gives a smooth flavour of olive oil to fried foods after it has been refined.

Gradings and taste

We should remember that the grade of acidity in an olive oil refers only to the proportion of free acid fats that the oil contains, which is always expressed in terms of grades, and nothing else. The acidity level is not indicative of the overall flavour of an olive. An extra virgin olive may have a very low acidity level but still have a strong flavour. Similarly, an olive oil with a strong flavour may also be of low quality. Above all, an olive oil must be pressed at the right time to produce the best from that particular crop. The basic elements to be judged in any oil are taste, aroma and colour. In virgin and extra virgin oils, these have a range of between 5.5º and 6.5º. It also has a short shelf-life, like some wines and sherries. Within a year or year and a half, it becomes rancid.

Virgin and extra virgin olive oil: oil produced by natural means, without any contact with organic solvents and with a temperature during extraction less or equal to 35 Celsius. Suitable for consumption on production. Olive oils of this quality can carry a 'denominacion de origen' qualification.

Refined virgin olive oil: An olive oil derived from simple and clear olive oils, not suitable for immediate consumption. Obtained by refining to make it edible, but it is not normally sold to consumers.

Olive oil: A mixture of refined olive oil and virgin or extra virgin olive oil. Also not suitable for immediate consumption.

'Orujo' olive or crude olive oil: made from the 'orujo' liquid byproduct of olive oil, which requires organic solvents for extraction and therefore is also not suitable for immediate consumption.

Refined 'orujo' olive oil: Oil derived from crude 'orujo' olive oil, not suitable for immediate consumption, but not normally sold to consumers.

'Orujo' olive oil: A mix of refined orujo olive oil and virgin or extra virgin olive oil, which is sold to consumers, but is not suitable for consumption, except when used in cooking processes.

All of the oils except virgin and extra virgin are graded as suitable for immediate consumption once they have been refined and mixed, in different proportions, with virgin and/or extra virgin olive oils.

 

Colour and varieties

Even though colour does not form a part of the sensory analysis of olive oil, the tones it acquires cover a wide range of yellow or golden transparencies in appearance. These vary between a golden yellow, which generally corresponds with the very sweet oils that are produced from olives harvested late in the olive season, that is to say, past their ideal maturation date, to a colouring more yellow-green in tone, from younger olives, with a touch of bitterness to the taste, a consequence of using olives from an early harvest, before they have reached maturity. In any case, in part because some consumers will buy depending on the colour of an oil, there are olive oil producers who are prone sometimes to modify an oil’s colour to give it a colour that will make it more attractive to buyers. This practice isn't particularly important because when the discolouration of an olive oil passes a certain determined point, the olive oil will lose the vitamin A content that gives it much of its qualities. A classification of olive oils is determined by the number of varieties of olive that are used in its production. If only one type of olive is used, it is called a 'monovarietal' oil. If it is the result of a mixture of two or more olives, chosen to stabilize the qualities of both or each different olive type, that is, that they do not produce a change in qualities when one is added to another, it is spoken of in terms of the French coupage, blending or infusing, as in oenology, 'wine science', or wine culture.

Lastly, because refined oils and orujo oils are not suitable for direct consumption, this does not mean that they are unhealthy. They are simply very low quality oils that must be mixed virgin or extra virgin oil to be considered as good enough for consumption.