The preparation of paste includes two fundamental phases: grinding and beating.
The purpose of grinding is to break up the plant tissues and release the oil droplets that are between these tissues within the pulp.
This operation can be done with the classic "curres" (conical shape grinding stones) or other stones, or with metal mills, usually the hammer mills.
The purpose of beating is to bring the small oil droplets into contact with each other so that they gradually form larger and larger droplets, until you have a continuous phase of oil. For this purpose, mixers that slowly turn and move the paste, are used. They bring the drops of oil into contact with each other.
Once the paste is prepared, it is necessary to separate the different elements that make it up: on the one hand, the liquid phase (oil and vegetable waters); and, on the other, the solid phase (pinyolada).
The way these two phases are separated is the main difference between the extraction systems.
The extraction can be done by applying pressure to the paste (traditional or pressed system), or by applying a centrifugal force (centrifugation applied in a continuous system).
Once the solids have been separated from the liquids, it is necessary to finish the process with the separation of the components of the liquid phase that are left, that is to say, the oil on the one hand, and the morca (lefover water on the other).
This separation can be done by decantation or by centrifugation.
The system of separating the liquid phases by decantation is prefered in traditional systems.
The actual decantation is the process of separation of the oil and the morca, due to the difference in densities that exists between the two.To achieve this separation, the oil must pass successively through a series of settling basins. In this way the finer solids are deposited and separation is made between the oil and the morca.
The other way of separating the liquid phases is by centrifugation and is used both in the continuous system and, more recently, in the traditional system. It also consists of a separation of the oil and the morca due to the difference in density and the application of a centrifugal force, which makes this separation faster.
As we have said before, the oil that comes out of our mills is the virgin oil, the oil obtained by squeezing the olives without any other processes that effect the oil.
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