The different phases from the elaboration process of the olive oil can be outlined as it follows:
• Reception, washing and storage of the fruit.
• Preparation of the pulp of which the oil will be extracted by milling and shaking.
• Separation of the residue or solid phase of the mixture from oil and water of vegetation (alpechín) or liquid phase, by pressure or centrifugalization.
• Separation of the oil from the water by decanting or centrifugalization.
• Storage of the obtained oil.
In order to assure the quality olive oil it is precise to count, at least, on two reception areas: one for the fruits that potentially can provide oil of quality, that is to say, healthy olives, harvested from the tree in a condition of uniform maturity, etc.; and another one for the fruits that hardly can provide good oils (coming from the ground, attacked by diseases, etc.). They immediately would be due to pass to the washing stage, but if being necessary to store, because the oil mill does not have sufficient capacity of storage, it would be the olive of bad quality the one that would have to be stored.
Traditionally the agriculturist has cleaned the fruit in the field by means of the use of sieves, but this cleaning was not complete, in such a way that the fruit entered the oil mill with a great amount of impurities, leaves, branches, mud, that was precise to eliminate. For it, in the first place cleaners are used which, by means of vibrant sieve and airflow, eliminate leaves, branches, etc. and then, if it is precise, washing machines are used that eliminate stones, dust…
After the cleaning and washing lines the olives are brought on to scales for the taking of samples and the weighting of the fruits, with the purpose to pay to the agriculturists according to the given olive kilograms. Once cleaned and weighted the fruits are stored in hoppers waiting for milling. It is very important that the storage time is as short as possible – the ideal time is less than 24 hours – to avoid alterations of the olives that would produce oils of greater acidity, minor stability and worse flavor.
The oil is in the olive in form of drops and to extract it is necessary the milling of the fruit to destroy the vegetal weaves that store these drops. This operation can be done by different procedures. Traditionally rotation mills have been used, but they are being replaced by the metallic mills, usually composed by hammers. Milling takes place by pressure of the rollers on the wall-plate or by action of the hammers that turn very quickly, when the olives are introduced in the camera. In both cases a pulp is obtained, that is more or less fine depending on the milling degree. If the milling degree is too heavy the industrial output is too low and if it is excessively fine emulsions can form which are difficult to deal with.
The pulp is introduced then in a beater, which is a deposit of variable capacity, whose mission is to turn around the pulp to do the separation of the oil easier in the following processes of elaboration.
After the beater the pulp is prepared to be processed by pressure (according to the traditional system) or by centrifugalization (according to the continuous system) and to extract the oil.
Until some years ago all the oil mills used the extraction system by pressure that consisted of the separation of the liquid part of the pulp, constituted by the mixture of the oil with “alpechín” of the olives, of the residue or solid part by means of a filtrate process favored by the pressure. The most common press consisted of two smelting bridges united by four steel columns and a piston that moves within a cylinder. The pulp was distributed upon porous plastic or vegetal fiber discs that have the name of “capachos”. The “capachos” with the pulp were piled up upon others until forming a tower that was denominated “cargo”. So that the “cargo” was vertical the “capachos” had a central orifice and they were introduced in a metallic needle.
Progressively the pressing system has been replaced by a centrifugalization system, in such a way that the oil mills have changed their traditional presses by horizontal centrifuges that are denominated as “decánteres”. When putt under centrifugalization the mixture constituted by elements of different densities, the different substances that compose the mixture separate in layers based on their density. In the case of the first “decánteres” of three phases, the mixture was constituted, in sequence of density from largest to smallest, by residue, “alpechín” and oil. At the moment the “decánteres” have two exits (two phases), one by which it leaves the oil and the other by which it leaves the mixture residue and “alpechín” (“alpe” residue).
Independent of the system used already we have separated the solid part of the pulp from the liquid part. In the centrifugalization system the amount of “alpechín” that takes the oil is inferior to the obtained one by the system of presses, which causes that the quality of the oil is better because goes less time by in contact with the waters of vegetation that can communicate bad scents and flavors to the oil. The following phase of the process consists of separating the liquid parts of each other, that is to say, the oil is going to be separated from the water. This can be done by means of three systems: decanting, centrifugalization and mixed system.