Extraction is the process of dividing the oil must – that is, the unfiltered liquid part – from the pomace – that is, the solid part containing fragments of kernels, peel and pulp. There are three methods for performing this process of extraction: extraction by pressure, extraction by centrifugation and extraction using the Sinolea method.
Extraction by pressure
This type of extraction is the most classic method, in which the paste obtained by kneading is spread on circular filtering diaphragms, arranged in a tower. These cylinders, which rotate on a pin, press the olive paste, forcing out the liquid part.
This type of extraction has its pros and cons:
The pomaces maintain a good quality
The energy and water used are reduced
The vegetation water to be disposed of is less than with the other systems
The vegetation water has a lower polluting load
High labour costs
High costs of cleaning machines
Discontinuous operating cycle
Risk of deterioration of quality due to paste residues in the cylinders
Extraction by centrifugation
This type of extraction is part of the continuous cycle process. In this process, the pulp is pushed, together with a defined amount of lukewarm water, inside a cone-shaped centrifuge where, through a physical effect, the separation of the paste from the must takes place.
This process also has its pros and cons:
Low need for labour
High labour capacity
Low degree of oxidation, which leads to a discreet oil quality
High costs of disposal of vegetation water and greater pollution
High drum maintenance costs
Greater water consumption
Extraction by the Sinolea method
This form of extraction consists of placing a device in a tank containing the oil paste. In order to separate oil and vegetation water, this process exploits the surface tension of the two elements involved: oil, which has a lower surface tension, tends to stick to the extractor, which has a metallic surface.
Like the other types of extraction, this technique also has its pros and cons:
Oil with a very high quality, due to the absence of alterations
Totally cold processing
Oil completely free of water, therefore does not require a centrifuge