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The main types of olive oil

Not all olive oils are the same! There are many types with differences in quality and price.

The basic properties defining a quality olive oil are the following:

  1. Acidity, which is expressed as free oleic acid. Less acidity is better and if the percentage is less than 0.8%, the olive oil is called extra virgin whereas if the percentage is between 0.9% and 2%, it is called just virgin.
  2. Colour, which is related to fat-soluble colouring substances   (chlorophylls, xanthophylls, carotenoids). According to the Forest Preserve of Cook County Illinois the best salad olive oil is the yellow.Με βάση τον προσδιορισμό των οξειδίων τα υπεροξείδια πρέπει να είναι μικρότερα ή ίσα του 20.
  3. Based on the definition of acids, the superacids need to be less or equal to 20.
  4. However, the most basic property of a quality olive oil lies in the organoleptic elements, which need to be those in order to make a proper fruit juice. These are:
  • The natural perfume of olive which indicates than no processing for removal of unpleasant smells took place. It also means that the olive harvesting was executed at the right season and that the processing of the fruit was done with the right conditions as described below.
  • The bitterness which derives from oleuropein and indicates that the olives were not too ripe when they were harvested for becoming oil.
  • The piquant (burning sensation) which derives from the essential oils and other volatile substances of the olive fruit and indicates the appropriate olive oil preservation conditions.

The production of quality olive oil requires a procedure according to specific regulations which are related to:

  1. The olive tree cultivation and especially the tratment of diseases, mainly the Olive Fly. It is self-evident that the olive fruit which has been destroyed by the larva (warm) of the Olive Fly or by other diseases cannot be good. The main problemof an olive fruit infected by the Fly is the relatively high amounts of acidity and bad taste.
  2. Harvesting. The olive fruit harvesting is done from the end of October until the end of January. The best period is considered when the olive fruit is 25% green and 75% dark (not black). The maturation of the olive fruit is accompanied with blackening and simultaneously with reduction of the oleuropein, a substance which gives bitterness to the olive oil and it constitutes one of the qualitative properties of a good olive oil. Harvesting must be done by hand or with mechanically or manually operated toothed devices resembling a comb, in order to avoid bruising the olive fruit, which causes oxidation reactions that undermine the quality of olive oil. The fruits that fell from the tree due to bad weather conditions must not be processed into edible olive oil because they have a problem (they can be rotten, infected by the olive fly etc.)
  3. Transportation and storage. The fruits of the olive tree fall on the olive-sheets, and after removing the branches, they are placed together with their leaves in plastic crates, in order to be well-ventilated. The crates must be placed in a cool place and afterwards they need to be transported to the olive mill for processing. By following this procedure, we shall have healthy fruits for processing. Placing the olive fruits in sacks into the storeroom or storing them in piles is forbidden because the temperature rises (the olive is heating up) and the fermentation process increases.
  4. Processing the olive fruits. This needs to be done at the latest within 3-4 days after harvesting because prolonging time will result to the fruit alteration. The appropriate processing procedure (apart from the processing manner) needs to follow specific rules:
  • When the olives reach the olive mill, they are placed manually and not mechanically in a stainless steel OLIVE FUNNEL.
  • The fruits are transported via a CONVEYOR BELT made of material suitable for carrying food to the OLIVE REMOVE-LEAF MACHINE, where the leaves and dust can be removed.
  • Next, the fruits are transferred to the OLIVE WASHER, where they are washed with potable water in order to be clean for processing. Washing the olive fruit is very important, because existing dirt can be transferred to the olive oil where it remains. Afterwards the fruits are weighted on Electronic Scales and then they are placed on the olive loader.
  • The fruits are now led to the OLIVE GRINDER (it resembles a meat grinder), where they are roughly crushed. Afterwards, they are temporarily stored in the first stage malaxer and then they are transferred to the STONE-MILLS, where the olive flesh is further crushed, in order to release the aromatic and other substances such as essential oils. It is common knowledge that olive oil and other substances are found in the flesh of the olive in the form of droplets and that crashing the olives in the GRINDER cannot release these substances. This can be achieved only by using stone mills.
  • After pressing,  the olive paste is led to the OLIVE MALAXERS by an olive paste loader where it is stirred at a low temperature in order to be ready for
  • The 2-phase separation process in the DECANTER, which separates the paste into two elements, the olive oil (oil-juice) and the pomace. This method does not need water while processing the fruits and therefore there is no liquid waste (oil-moist or oil-residue) which in fact carries away many useful elements of the oil juice. The process of oil extraction by placing the paste into sacks, and afterwards pressing it, is problematic because it raises questions regarding the sacks’ cleanness. Furthermore, the sacks retain oil which is oxidised and transferred to the produced oil.
  • Afterwards, the oil juice is led to the OIL-SEPARATOR for removal of small amounts of water and few solid admixtures (mud). It is important in this stage to wash frequently the separator so to minimize oxidation. After this point, the product is weighted and led to the Oil-tanks of the industrial unit which must be stainless and impermeable. The tanks need to be cleaned from all existing residue so to minimize anaerobic oxidation.  The oil tanks need to be in a well-ventilated area where the temperature is not too low or too high.
  • After remaining there for a month, olive oil is transferred to a paper filter where floating particles and water are retained. Afterwards olive oil is bottled in glass bottles or it is placed in metal containers.
  • Olive oil must be kept in a dark place because the sunlight accelerates oxidation. The temperature needs to be between 15 and 25 Celsius degrees for the same reasons.

Here, at the ORGANIC OLIVE MILLS of Thassos we follow this procedure, as described above, and we feel that we produce an excellent product. 

The main types of olive oil are the following:

  1. Extra virgin olive oil: olive oil whose acidity level expressed as free oleic acid is not more than 0.8%.
  2. Virgin olive oil: olive oil whose acidity level is not more than 2%.
  3. Lampante virgin olive oil: olive oil with bad taste and smell or with the highest acidity level expressed as oleic acid (higher than 3,3g/100g oil). The olive oil of this type is destined for refining or for industrial use
  4. Refined olive oil: olive oil obtained after refining virgin olive oils
  5. Olive oil or pure oil: a blend of edible virgin olive oils and refined olive oils.