Extra Virgin Olive Oil: the production techniques
The information in this article are neither exhaustive nor detailed: they are outlined information to show the idea what is behind the production cycle of such a valuable food.
In the following there are listed the operations inside an oil manufacture to get an Extra Virgin Olive Oil (EVOO) of superior quality with the desired organoleptic properties.
STORAGE OF OLIVES IN OIL MILL
After harvesting, the olives storage must be done for a short time, not more than 24-48 hours. Usually perforated crates or perforated plastic bins are used to store olives; these are well suited to protect olives from avoiding layers of excessive thickness. The bins guarantee ventilation and can be easily moved mechanically. The olive storage must be done into ventilated rooms, away from humidity, from extreme cold and extreme warm temperature values (not over 20°C) who can damage olives by mold growth.
OLIVES DEFOLIATION AND FLUSHING
To get a high quality EVOO the olives must be defoliated and flushed both for hygiene and sanitary reasons and mechanical reasons. To clean properly the olives it is used drinking water renewed often to guarantee the complete hygiene of operations.
GRINDING AND CRUSHING OLIVES
The main and most important operation to release the oil from olives is the grinding (molitura), or crushing (frangitura); this results in breakdown the cells of olive flesh containing oil. Crushing is carried out by means of traditional granite millstones or by means of metallic crushers. The granite millstones crushers have low working capacity with a slow and not violent action; this kind of operation ensures a good dough preparation and achievement of harmonic and balanced oils, with less intense bitterness and pungency taste. The metallic crushers have more high working capacity because they crush the olives at high speed exerting a more or less violent action depending on crusher type (fixed or mobile hammers, toothed disks, knives, cones, rollers). The oils obtained by means of metallic crushers have more intense bitterness and pungency taste and richer in biophenols (from non-blackened or slightly blackened drupes) and that are thus very preservable.
MALAXATION OF THE OLIVE PASTE
The final preparation of the olive paste is carried out with the operation of malaxation: this is a slow and continuous movement of the pulp generated by the rotation of helical ribbons and blades welded on a horizontal axis which rotates at 20-30 revolutions / minute.
The malaxation machines are hermetically sealed, they have semi-cylindrical shape, are made of stainless steel and are equipped with external jacket for the circulation of warm water needed to heat up dough to a suitable temperature, in dependence of the extraction system adopted. The slow and continuous kneading of the olive paste disperses the emulsion formed form crushing process and facilitates the formation of oil drops. The malaxing temperature must be take under control to get an adequate olive paste. The temperature must not exceed 28-32 °C whatever the system in the oil mill. In case the producer want to distribute the EVOO labeled as "cold pressed" ("estratto a freddo" or "prima spremitura a freddo") the malaxing temperature must not exceed 27 °C.
OIL SEPARATION FROM OLIVE PASTE
The olive paste coming from malaxing phase is ready to separate oil from paste; this is done by means of a mechanical system able to exert a physical interaction on paste and get the separation of liquid components from solid one. The main systems adopted are pressure, percolation and centrifugation
PRESSURE
This is the oldest and traditional method to produce oil form olive paste. The oils obtained with this system are high quality oils with harmonic and balanced tastes; this result is due overall for use of granite mills during the grinding phase. This system requires special care and attention to assure and maintain the cleanliness on the surroundings and the machines, overall about dyaphragms (fiscoli), to avoid oil contamination due to volatile substances coming from organic substance transformed by microorganisms living in the olive paste and in the environment where olive paste is worked.
PERCOLATION (OR SELECTIVE FILTRATION)
This system is based on the principle that when a steel plate is plunged into olive paste the oil adheres to the steel. This system is generally combined with cetrifugation and oils resulted are maximum quality depending only on olives quality: the slow movement of thousands steel plates does not require intermediate means (water or filtering dyaphragms) to extract oil. This system also requires attention and maintaining of the cleanliness of the thank where steel plates and scrapers works for extracting oil. This system is not widely used.
CENTRIFUGATION
The more widely used system for olive processing is the continuous olive paste centrifugation by means of high speed rotating horizontal axis decanter: this systems require additional water to thinning the olive paste. The modern and innovative decanters can separate oil form olive paste using low or null quantity of additional water and allow to avoid the production of vegetation water. The oils resulted with this processing system have high total content of biophenols.