Elaboration Olive oil

1. Olive oil

Olive Oil. It is the only obtained oily juice from the fruit of the olive (Olea europea L.) with the exclusion of those obtained with solvents, procedures and re-esterification of any mixture with oils of other kinds. It is marketed under various designations and definitions. Among all, the most important thing is virgin olive oil that is obtained from the fruit of the olive tree solely by mechanical methods or other physical means under conditions, especially heat, which has had no treatment other than washing, decantation, centrifugation and filtering.

The oil constitutes the 15-26% of the olive and it is in the vacuoles within the cells of the olives. The olive oil production consists of the separation of the oil contained in the fruit of the solid components and the water of vegetation of the olives.

2. Processes of Extraction

For the extraction of the olive oil two processes are used, one is based on the separation in a horizontal centrifugal machine (Decanter) of the three present phases in the olive (oil, water of vegetation and solid), the other (of two phases) separates the oil of the rest of component presents in the fruits (solid and vegetation water). Still in some places the call is used traditional process in which the oil is obtained by means of press.

Wash and Heavy

When arriving the olives it is necessary to retire the dust and other substances to him that can bring like leaves, earth, stones, branches… These processes are realized with automatic machines that clear the leaves by means of ventilators, next the olives are washed in a rotatory drum in which the water circulates and in that the heaviest materials separate. After the washing the olive is heavy to know the amount of clean olive that contributes each partner.

2.1 Traditional process

EIn this process the liquid phase (Olive oil + vegetation water) separates of the solid phase of the olives by pressure. Later the separation of the contained olive oil is realized in the liquid obtained in the pressing by movement.

• Milling

  The olives are crushed in mills. The objective is to break the cells of the pulp to leave the oil leaves the vacuoles, allowing therefore the formation of drops greater than can separate of the other phases. In this traditional process the olives are crushed generally in stone mills.
  In these devices the fruits wear out without an excessive mechanical tension, forming emulsions that make difficult the separation of the oil, in addition is no metallic pollution hazard. Normally it consists of trunkated cone a cylindrical granite base on that they are had 2 to 4 cylindrical stones or that turns around an axis at a speed of 12-15 rpm.

• Beaten

  Once ground the olives, it grazes obtained must be shaken slowly (milkshake), this process consists of which shovels move continuously grazes in semicylindrical or hemispheric containers. These equipment has a heating system in their inner walls around which hot water circulates, their inner walls are of stainless steel to avoid the possible metallic contamination.
  The fundamental objective is to increase the size of the drops of oil so that they can separate more easily, in addition, break the emulsions oil/water. With the use of presses the duration of the milkshake is of approximately 10-20 minutes.

• Pressing

  The extraction by pressure is the oldest method used to extract the olive oil. One is based on the principle of which when the olives are squashed (pressing) frees the liquid phase (the water of vegetation and the oil), separating of the solid phase.

  

  Of the press the extraction consists of the application of pressure to a filter disc battery, between each two of them has a layer grazes of olive. All this, is placed on a car that takes a central axis.
  The press can apply to a pressure of 120-200 Kg./cm² and the process of hard extraction around 1-1,5 hours.

  With the introduction of semiautomatic machinery to clean and to load the capachos, a considerable saving of the costs takes place.

• Decanting

  With the pressing of it grazes of olives obtains a liquid that olive oil contains, vegetation water and a small amount of solids that escape in the press. By means of a revolving sieve it is come to the retirement of those these solids. Letting rest the obtained liquid mixture with the pressing, one obtains that the oil is in the surface because its densidad is minor who the one of the vegetal water.

  

  The decanting process consists of having a series deposits connected mutually. The oil passes of deposit in deposit through the part superior, taking place the sedimentation of the water, the vegetation water circulates in sense opposed by means of siphons in the part inferior of the deposits, and so it is able to maintain in the surface the greater possible amount of oil.

2.2 Process of three phases

The extraction of oil per centrifuge olive paste and obtaining separate oil, water, vegetation and the solid residue (Orujo) is done through a process that takes place in modular plants working continuously.

The phases of this process are:

• Milling. Most habitual in continuous systems it is the use of metallic mills (Hammer, teeth, discs, cylindrical or of rollers) to crush the olive. In these metallic mills it is possible to determine the size of obtained fragments since it has a grid that only allows to pass smaller fragments of that size in agreement with the later system of extraction that is applied. This system has an advantage since when working in continuous it has a smaller cost and major yield, occupying a smaller space than the stone mills.
• Beaten. The use of mill of hammer for the olive milling can give rise to the formation of emulsions between the oil and the water, is reason why it is necessary to realize the milkshake of grazes to increase the size of the drops of oil. This process is slightly realized to temperatures superiors to the atmosphere and its duration, in no case, must be smaller of one hour. The modular plants of oil extraction consist of two or three units of mixture (beaters) that consist generally of cubas horizontal semicylindrical which they have an outer camera by which hot water circulates to maintain grazes to the predicted temperature. Within the beater it grazes of olive stays in movement by means of a device that turns around the axis. If a temperature rise takes place in which is realized the milkshake it increases the yield of the extraction. The most efficient temperature is between 30-35ºC.
• Centrifugalization of grazes. In this process the liquid phases separate of the solid phase by means of the application of centrifugal forces that increase the differences between the special densidades of the oil, water of vegetation and the solid matter. This process is conducted in a horizontal centrifuge. It consists of a rotor Cylinder scraper and a conical-helical hollow shaft, which turns coaxial inside the same. The difference in speed between one and one makes the solid Terraced on the inside of the rotor and are drawn towards one end by the screw endless. The liquids (oil and the liquid phase) form concentric rings more interior according to their density and leaving abroad for various pipelines. For a better separation of the components is necessary to add water to the paste that comes from the blender. The amount of water that is added influences the performance of extraction. The best pulp / water can vary from 1:0,7 to 1:1,2 and is determined empirically observing the characteristics of oil and water leaving the decanter centrifuge.
  From decanter centrifuge leaving two types of liquids, one green formed by oil and some aqueous phase and the other brown constituted by the aqueous phase and some oil. Depending on the size machines on the market can process between 0.5 and 4.0 tons of olives per hour. The advantages of this system are that the machines are compact and require little space, is a semi-automated process, yields a higher quality oil than in the press and less manpower. The disadvantages are that it is expensive, requires a more specialized workforce, needs more consumption enrgía and hot water and produce a greater volume of wastewater to be disposed in evaporation ponds.
• Centrifugalization of the liquids. The decanting requires a large space and a large number of deposits, which is why since 1970 using centrifugal force to separate the oil content in the two liquid phases that are broken into the decanter centrifuge. ABoth liquids are put under a centrifugalization in two plate centrifuge, this way the part of oil recovers that accompanies the watery phase (the one of brown color) and by means of the addition of a certain amount of water part of the humidity retires and the oil of the oily phase is cleaned. It is necessary to eg: consider a series of factors for a good separation the homogeneity of the liquid, the volume of feeding, the temperature, the volume of the added water and the time between unloadings. With the centrifugalization one has been able to increase the amount of oil produced in zones where the yield was low.

In short the quality of the obtained oil depends on the used system to process the olives. In the process to three phases the number of present natural antioxidants in the oil due to the added water is reduced to dilute grazes of olives. Nevertheless the chlorophyllous pigment content is but high in the oil obtained in modular plants because in the milling in the hammer mill more chlorophylls than in of stone are freed.

The biggest problem in three phases of the process is the high volume of wastewater that is generated (alpechin) (1,2-1,3 litres / kg. Olive processed), due to the addition of water that is made pasta of Olives before entering the horizontal decanter.
These liquids have a high pollution and high concentration in poly phenols that prevent its purification by conventional means, which must deposit with evaporation ponds for the increase in costs, health problems and visual impact.

2.3 Process of two phases

Due to the high volume of waste water generated by the process to three phases, which brought about a great problem to them, it was reason why the new models arose from horizontal centrifugal decanters that were able to separate the oily phase of grazes of olive without requiring the hot water addition. This implied that liquid spills would not be producieran having the solid remainder a major contained in humidity.

The extraction of the olive oil by the system of centrifugalization of two phases takes place in modular plants that work in continuous and in the same they are obtained separately, on the one hand, the oil and, on the other, grazes fluid (alperujo) that contains the water of vegetation and the pulp.

Two first stage of this process is realized of form similar to those of the system of three phases, the unique difference is in the centrifugalization of grazes and the subsequent centrifugalization of the resulting oil.

• Centrifugalization of grazes.

  In this process the oily phase separates of the olive (pulp + vegetation water) as a result of the centrifugal force that increases to the difference between the specific densidades of the oil and alperujo (solid matter plus the vegetation water). This process is realized in a centrifugal decanter horizontal similar to the employee in the system of three phases. The applied value of G is superior in the centrifuge of two phases (3000-3600) that in the process of three phases (2000-2600). This value G depends on the turnover rate and the inner diameter of the rotor.
  In this case it is not necessary to add water to secure one better separation of the oil. Like the oily phase that leaves the decanter can take solid particles, he is advisable to have when coming out the oil a vibratory sieve to separate the small pieces of pulp or bone.

• Centrifugalization of the liquids.

  The oily phase is put under a centrifugalization in a plate centrifuge, in this operation certain amount of water to the oil is added in order to wash it and to be able to retire part to him of the humidity that brought of the decanter, this water is the unique spill that is generated in this process of extraction of the oil.

  

  In short the process to two phases has a yield superior that the one of three phases due to the fact that in the new system water is not added to grazes and the formation of emulsions is avoided oil/water.
  This process does not produce as soon as spilled, only originates a small volume of the water added in the washing of the oil in the centrifugalization, being avoided the problems of environmental that are originated by the great dimensions that they must have the evaporation rafts.
  The quality of the produced oil is superior to the obtained one in the process of three phases, due to the great amount of poli phenols and/or I gave phenols. It implies that this oil is more stable during the storage as they indicate the high values of the time of oxidating stability that are had in oils obtained by this system.

3. Storage of the oil

The tanks to store the olive oil would have to be constructed with totally impermeable and unassailable materials. The material used for the construction must present/display greater inertia with respect to the oil, so that this it does not absorb scents and defective flavors and do not dissolve substances that could contaminate or produce phenomena of oxidation (metal presence) in oils.

The tank must protect to the oil of the light and the air, since these factors accelerate the alteration of the product. In addition it must maintain the oil to an almost constant temperature (on 15-18ºC), avoiding abrupt changes. Low temperatures can bring about the freezing of the oil and discharges to contribute to their oxidation.
Until recently time the tanks that better met these conditions were the deposits buried with a suitable covering (generally refractory tiles).

At the moment stainless steel tanks of different capacities are used, normally of 50 tons.

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