The difference between the two processes
Extra virgin olive oil can be obtained using two similar, yet different processes: the first cold pressing or thecold extraction. The choice of the process influences the denomination of the olive oils and their quality.
First Cold Pressed
First cold-pressed involves the use of a hydraulic press to crush the olive paste. The pressure generated by the press causes the natural separation of the oil from the paste.
This process consists in creating a paste with the olives in a stone mill. It is spread over the mats, which are essentially pockets and filters stacked on each other in a hydraulic press. The mats are subjected to such a strong pressure that a liquid composed of water and oil flows out. This liquid is recovered and then decanted for the purpose of separating the two substances. Only the oil is kept to be bottled.
The first cold-pressed process is only rarely used for olive oil production nowadays. Cold extraction is preferred because it is cleaner and ensures better control over the manufacturing parameters. The presses and stone grinders have almost all disappeared for the production of olive oil, only to give way to mixers and centrifugal pumps.
The cold extraction involves the mixing of the olive paste in order to extract the oil in the form of fine droplets which stick to each other.
Traditionally, the olive paste was formed with a grindstone, just like for the first cold-pressed process. However, the risks of the oil oxidizing and of its aroma being adversely affected were deemed too great. Centrifugation became the preferred method, in order to reduce those risks as much as possible.
With this technique, the olive paste is produced in a mixer that grinds the olives at a temperature around 27 °C. It is then put into a centrifugal pump so that the oil, solid residue and water can be separated. Once all the oil has been recovered, it is packaged in dark glass bottles.
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