Extraction of the olive oil

The extraction of the olive oil is the industrial process, carried out in a Moulin with oil, from which the object is to extract the oil from the Drupe S of the olive-tree. This process includes/understands two fundamental stages: preparation of pulp ( crushing ) followed separation of the oily fraction of the other solid-state devices and liquid ( extraction itself).

Basic principles

The olive oil itself is contained in the lipovacuoles cell S of the Mésocarpe ( pulp ). The process thus envisages the extraction of the liquid phase of the cells, the separation of the solid fractions and the separation of the lipidic fraction of the aqueous fraction. The “virgin” olive oil is distinguished clearly from the other types of oils by two characteristics: raw material, consisted the pulp of olives, the method of extraction, made process of nature exclusively mechanical.

The extraction of the unrefined olive oil calls exclusively upon the Choc, with the Pression, the Centrifugation, the Décantation, the Filtration, the surface Tension and with the mechanical treatment of the emulsion S. the recourse to the heating is allowed, at moderately raised temperatures, in order to increase the oil yield.

Other techniques envisage the use of physical and chemical methods. However the regulation and the quality standards impose the exclusive use of mechanical methods. The oil obtained by the recourse to chemical and physicochemical methods is thus identified with types of products different and distinct from the unrefined olive oil. In the case of the olive oil, the physical and chemical methods are secondary processes implemented in distinct installations, to rectify nonedible unrefined olive oils or to extract the lipidic fraction from seeds.

Phases of the process

The production lines by mechanical extraction differ by the methods employed in the various phases, it thus exists as many types of different installations. In addition to their features, the installations differ from manner marked by production capacity, the level of mechanization, the organization of work, the qualitative and quantitative output, the production costs. In general, all the installations comprise the succession of four fundamental phases:

preliminary operations: they have the aim of preparing olives following work;
crushing: it has the aim of breaking the walls of the cells and to make some leave juices. The product of this phase is generally called paste ;
extraction of the oil must: it has the aim of separating the liquid phase, the emulsion water-oil, of the solid phase, the Grignons . Those are composed of the solid residues of the skins, pulp, seeds and the fragments of the cores (oil cakes). The emulsion water-oil is generally called must of oil or sometimes juice of olives . Actually, must contains also a solid residue, the “deposit”, which remains in suspension in the emulsion;
separation of oil and water: it has the aim of separating the two components from the oil must. During this process one separates the two nonmiscible liquid phases and most of the deposits. One names the residual aqueous phase " the Margines " (not of use in the singular).

Preliminary operations

Before the extraction itself, the olives must be prepared, it is the object of the preliminary operations. They are operations intercalated between the harvest and crushing carried out in the initial part of the Moulin to oil.

; Sorting It consists of a cleaning of olives to separate them from the ground, small branches and sheets. This operation can be done directly with harvest, at once, or, for minor amounts collected with the hand, on the ground in a room of the exploitation before the delivery or, in general in the co-operative mills, at the time of the delivery. The sorting of larger quantities is carried out using static or vibrating screens. Formerly, some tended to leave an minor amount of sheets with an aim of giving to oil a fruitier taste.

; Weighing It is done with the mill with oil, at the time of the delivery. In Italy, the structure of the die, primarily made up of olive-growing small-scale farmings which deliver their harvest to co-operative mills or which operate for the account of third, makes that the delivered quantities are generally modest quantity (1 to 1,5 T to the maximum). Weighing is thus done after the unloading of the freight vehicle out of crates, palox or bags.

; Storage In the case of batches of low importance, collected completely with the hand, this phase proceeds partly in the olive-growing exploitation with an aim of reaching the quantities necessary to deliver for a cycle of treatment. For more important batches, obtained in general by mechanized means, the collected olives are directly delivered to the Moulin with oil and are stored in a space or a separate room (the olivaio ), even directly in a space located at the beginning of the line of treatment. Formerly, one stored olives out of bags of Jute, currently one employs openwork cases or palox in the case of palletized systems, while reducing as much as possible the thickness of the layers to improve ventilation of olives and to prevent the risks of Fermentation.

; Washing It is done by immersion of olives in a water vat or, in the modern installations, ad hoc washerwomen who maintain water moving forced to improve the result of the operation. To obtain an oil of quality, it is important in this phase which water used is clean by frequently renewing it. At the end of the operation, the olives undergo a draining.

The quality of the finished product depends on the final operations in relation to the state of conservation of olives and the latencies. The conservation in important heaps, with an insufficient ventilation of the mass of olives and latencies about several days, cause the appearance of phenomena of Fermentation of the olives which very quickly modify the characteristics physicochemical and organoleptic of oil, and which involves a rise in temperature. The phenomenon is accentuated olives in the case of having undergone shocks during the harvest or of the attacks of the fly of the olive-tree. The current orientations are the following ones:

storage of olives in sufficiently broken down fresh medium and, not very thick layers;
reduction of the latencies at 3 a.m. to the maximum starting from the delivery.

Crushing

Crushing constitutes the first phase of the extraction itself. The olives are subjected to mechanical actions which cause the rupture of the cellular walls and the membranes involving the release of cellular juices and oil. This action is entrusted to the friction of the fragments of the core on pulp or to the shock of mechanical devices in rotation at high speed in the mass of pulp. The product obtained at the conclusion of this phase, in the majority of the installations, is a paste, the paste of oil , mass semifluide made up of a solid fraction (fragments of cores, skins and pulp) and of a liquid fraction (oil and water emulsion).

The systems used are basically of two types.

Edge runners

The grinding stone has been an instrument used for several millenia, which underwent many modifications with the wire of old It exists old grinding stones of various dimensions, conical cylindrical or cylindro-conical. The modern grinding stones always function on the same principle: the mechanical action is exerted by the rotation of one or more large stone wheels (generally in Granit) on the worked mass. As opposed to what one could think, the release of juices is not caused by crushing, but by the action of friction of the cutting edges of the fragments of core on the pulp of olives. The role of the wheels is thus to crush the cores in dimensions adapted to the objective and to mix the worked mass.

Formerly the grinding stone consisted of only one wheel actuated by means of an arm by a ass or a Cheval, and had an important volume of obstruction to allow the circular motion of the animal. The current grinding stone is driven by an engine from 5 to 12 kw and is of relatively limited size, of an obstruction from 10 to 25 m ². It is composed of a bottom vat of granite or steel and at the edges raised out of steel and of a unit from 2 to 6 wheels with granitic horizontal stone axis, laid out per pairs with variable spacings compared to the vertical axis of the vat. The plan of bearing of the wheels is raised of a few millimetres compared to the bottom of the vat and is adjustable so as to obtain fragments of cores of adequate size. In general the adjustment of the plan of bearing is made according to the characteristics of the cores of the prevalent variety of olive-tree in the zone of the mill. The grinding stone is finally provided with blades which have the aim of removing the paste which adheres to the wheels and to improve malaxation by pushing the paste under the wheels.

The work of the grinding stone is done with a slow rotation (12 to 15 turns per minute) for one variable total duration from 20 to 40 minutes. The quantity of olives treated in a cycle is from 2,5 to 3 quintals in order to obtain the quantity of paste corresponding to the load of a hydraulic press in the phase of extraction. This requirement is essential less in the case of the installations which resort to other systems of extraction and in general capacity for treatment is calculated so as to integrate the grinding stone in an extraction plant into continuous cycle.

Disc and knife, hammer mills

The entirely metal crushers are the apparatuses preferred in the modern installations with continuous cycle because they are integrated perfectly with the requirements of automation. It is composed of a series of metal elements turning quickly and provided with arrises (hammers or expensive following the number and the thickness), of which the number of revolutions is of 1200-3000 turns per minute. They are driven by engines of a power from 10 to 40 kw. With this system the rupture of pulp is caused by the shocks of the revolving devices at high speed and only partly by the mechanical action of the fragments of cores. The crushers with discs turn less quickly. The treatment is done in very short times, about a few seconds, and lends itself well to an operation in continuous cycle with loading and automated unloading. The obstruction is about a few square meters.

Comparison

The two systems have advantages and disadvantages.

Traditional crushing involves a small degree of emulsion what makes it possible to obtain qualitative and quantitative outputs higher. Quality moreover is improved with fruity the more intense because the processing times allow a more thorough action of the Enzyme S. the oxidation of the paste under the effect of the exposure to the air are a negative phenomenon and can have a strong incidence according to the method of extraction employed, however if the grinding stone is integrated in a system into cycle continuous or semi-continuous the quality of the product is generally high.

Crushing causes a degree of emulsion pushed between water and oil, offers weaker quantitative outputs and makes essential malaxation. The quality of the product depends in substance on the temperature adopted at the time of the following phase of malaxation, making necessary a compromise between output and quality. The advantages lie in the important time capacity of treatment, in the integral automation of the process, perfect integration in an installation with continuous cycle.

Oils obtained are different, those from the edge runners generally softer and are equipped with fruity not very herbaceous but nevertheless complex; those from the knife or hammer mills burning, bitterer and being equipped with fruity the vegetable. An expert taster is able to distinguish with tasting an oil produced using a grinding stone of another produced using a hammer mill, on the basis of these simple difference. A wise choice can be made by taking of account the organoleptic potential of the dominant variety of olive-tree, but also the undeniable advantage which the systems give to grinding stone with the image of the mill with respect to the customers.

Malaxation

It is an operation the purpose of which follows crushing or pressing and is to break the emulsion between water and oil and to make agglomerate the oil particles in larger drops which tend to separate spontaneously from the water of vegetation.

It is carried out in machines known as mixers . The mixer is in substance a steel container in which turn of the helicoid blades which maintain a slow movement of mixture of the paste. The action of malaxation breaks the emulsion by then improving the must yield of oil at the time of the following phase of extraction. The models currently built include/understand several mixers laid out in series (often superimposed to limit the obstruction) or in parallel and charged mechanically, using a hydraulic system, with the paste from the crusher or from the grinding stone. There exists moreover a category of mixer-batcher provided with a delivery system with the paste on filter diaphragms used in the extraction by pressure.

This phase has a great importance to determine the suitable compromise between quantitative oil yield and quality: reheating increases the effectiveness of malaxation by allowing the increase in the oil yield, it influences however negatively, with the top of a certain temperature, on the quality of oil:

degradation of the taste ( taste of heated );
loss of volatile substances and consequently of the taste of fruity;
intensification of oxidation;
less dietetic quality because of the losses in polyphenols, Tocopherol S and vitamine With.

For oils of great quality, malaxation proceeds cold or by moderately heating the oil paste until a temperature from 27 to 28 °C. A higher output can be obtained by heating the paste up to 29-30 °C, while it is but it is disadvised exceeding the 30 °C. The Règlement of the European Union n° 1019 of 2002 authorizes to be marked on the labels cold (in reference to the processes of extraction) only if the whole of the operations necessary to the extraction proceeded at a lower temperature or equalizes with 27 °C.

The effectiveness of malaxation depends moreover on the method used for crushing. The use of grinding stones creates a small degree of emulsion and consequently cold malaxation is sufficient to obtain a good oil yield. Crushing, under the effect the high speed of rotation of the hammers, creates on the other hand a more stable emulsion which requires a moderate reheating of the paste up to 28-29 °C to obtain an acceptable output.

Malaxation has one intermediate duration from 20 to 40 minutes. The prolongation of the operation does not have any effect on the oil yield, it is thus to avoid because it would prolong the contact of the oil paste with the air determining a greater oxidation. Malaxation must thus be stopped when the paste ceases staining the hands and becomes consistent with the touch. The modern installations have automated systems for the control of the phases.

Extraction of oil

It consists of the separation of the oil must and the Grignons, solid fraction consisted the fragments of core, of the skins and pieces of pulp. The extraction is carried out by various systems which call upon mechanical principles of different design. Because of these differences must and marc have different characteristics according to the method of extraction employed, but one must also highlight deep differences in the installation, the quality of the product, organization of work and in management itself. The methods of extraction are attached to three fundamental types.

Extraction by pressure

It is the old method, which separates must from oil of the oil cake by a filtration under the effect of the pressure. The pressure is obtained in a hydraulic press open by laying out the paste of oil in alternate thin layers with fiber discs, called Scourtin S, in a mobile tower. The device used for the construction of the pile consists of a circular steel plate at the edge slightly raised and profiled, assembled on a carriage for handling. Into the center of the plate a hollow roll is inserted (known as switches ) which has the aim of maintaining the pile in driving position and to also support the flow of the oil must along the central axis of the pile.

The construction of the pile respects a standard order: the scourtins are consisted a synthetic fiber disc bored in the center so as to be able to thread them on the needle. On the first scourtin, posed on the bottom of the plate, one lays out a layer of thick paste of 3 cm, one superimposes a second scourtin and a second layer of paste and so on. All the three layers of paste, one superimposes a scourtin without paste and a steel disc in order to distribute the pressure uniformly. Broadly one builds a pile formed by the superposition of 60 scourtins alternate with 60 layers of paste, 20 discs of steel and 20 scourtins without paste. The quantity of paste employed corresponds to a batch of olives crushed with the grinding stone (2,5 to 3 quintals). All the operation of loading of a press is done with the hand, but currently one uses special quantimeters, often integrated into the mixer. The tower is then inserted in the press and is subjected to an average pressure of about 400 atm. Under the effect of the pressure, the oil must separates from the solid fraction and runs out of the system draining along the external walls and the needle and is collected on the plate. Once the extraction finished, the pile is dismounted and one withdraws the oil cake of the scourtins using ad hoc machines.

In the past the scourtin was a double filter disc, made out of coconut fibers, welded onto the edge external and bored with the center. The paste was put inside the scourtin. This system presented many disadvantages. The operations of loading and unloading was rather expensive, but especially the principal defect lay in the difficulty of cleaning of the scourtins: the fibers always retained residues of paste which deteriorated easily under the effect of Moisissure S or oxidation and conferred on oil unpleasant savors ( taste of scourtin ). For organisational reasons and to improve the standards of quality, the scourtins completely abandoned and were replaced by circular synthetic fiber scourtins.

The advantages of the extraction by pressure are the following:

better oil yield;
good quality of the oil cakes;
low fuel consumption of water and energy;
less quantity of water of vegetation to be eliminated;
less polluting load of the water of vegetation.

The disadvantages are the following:

high costs of labor;
loads related to the difficulty of cleaning of the scourtins;
operation in discontinuous cycle;
risks of deterioration of the quality in the event of defect of cleanliness of the scourtins;
great difficulties, even impossibility to extract oil from the pastes with high water content (beginning of the season and varieties with poor yield).

Extraction by centrifugation

It is a method of great diffusion because it makes it possible to overcome the multiple disadvantages associated with the extraction by pressure. The oil paste is subjected to a centrifugation in a conical drum turning on a horizontal axis (decanter). Centrifugation is done at a number of revolutions of approximately 3400 turns per minute. Under the effect of the differences in specific weight, centrifugation separates two or three phases. According to the technical specifications, one distinguishes three fundamental types from decanter.

The decanter with three phases is the oldest type and it presents various disadvantages. Centrifugation separates three fractions:

oil cakes;
the oil must, containing an minor amount of water;
margines, containing an minor amount of oil.

This system requires the preliminary dilution of the paste with water. It presents considerable defects because it consumes important quantities of water and product of the high quantities of margines. Water has in more one action of washing of the paste which carries to the extraction of a great quantity of phenolic compounds. The margines have consequently a stronger polluting load what makes more expensive later elimination from there. For these reasons, the system with three phases is gradually abandoned.

The decanter with two phases at summer conceived to mitigate the disadvantages of the preceding system. In practice, it is different from it by a less use of water and a weaker oil yield. Centrifugation only separates two fractions:

oil cakes and margines;
the oil must, containing an minor amount of water.

This system reduces the problem of the polluting load because the quantity of phenols extracted is less. It presents the defect however to produce too wet oil cakes, not accepted by the installations of reprocessing because of its lower commercial value. The oil cakes become consequently a waste product to be eliminated without any possibility of economic recovery, drying being adapted little.

The decanter with two phases and half is the most recent type and it takes again the merits of the two preceding systems. The treatment requires the addition of a reduced quantity of water and separates three fractions (wet oil cake, margines, must of oil). The advantage of this system is that it produces a less quantity of margines and with a more reduced polluting load. The wet oil cakes still have a low value, however it is possible to treat them by systems which allow an economic recovery by exploiting the natural energy of the oil cakes.

Advantages:

great capacity for treatment;
less need for labor thanks to automation and to operation in continuous cycle;
good quality of oil thanks to the small oxidation step and facility of cleaning;
obstruction limited of the installations.

Disadvantages:

high energy consumption;
consumption of high water;
maintenance costs raised because of the wear to which the drum is subjected;
costs of elimination of the effluents because of quantity of water of produced vegetation and of the higher polluting load;
difficulties of management of the oil cakes.

Extraction in Sinolea

The Sinolea is a device integrated in an installation specific to continuous cycle which is based on a flow diagram for treatment different from the other installations. The physical principle at the base of Sinolea is the difference between the surface Tension of water and that of oil: because of this difference, oil tends to adhere to a metal surface more easily than water.

Sinolea consists basically of a tank containing the paste, resulting from a hammer mill, in which the device extractor is immersed. This last consists of a series of steel blades which are immersed in the oil paste by a regular reciprocating motion which alternates the following phases:

immersion;
rising;
scraping of oil.

With each cycle of immersion, the rising of the device made drain the water of vegetation under the effect of gravity while oil adheres to metal surfaces. During the movement of return surfaces metal come into contact with a scraping device which removes oil by making it join in a system of collection. This system makes it possible to obtain an oil of high-quality very, however its output is rather weak. If it is interesting on the economic plan, the residual paste can be subjected to a second process of extraction by centrifugation. In this manner, one obtains two products differentiated in terms from quality.

Advantages:

great quality of oil;
cold treatment;
automation of the process and integration in a continuous cycle;
reduced labor;
must of oil without water, therefore not requiring secondary treatments.

Disadvantages:

reduced output;
required to combine the installation with an additional device for the recovery of the fraction of residual oil;
potential exposure to the processes of oxidation because of the greatest contact with the air.

The Sinolea system profited from a strong passion before the decanters 2 phases do not appear. It indeed made it possible to extract most of oil before the water addition when it was coupled with a decanter 3 phases, while decreasing the labor vis-a-vis the system with presses, or to extract most of oil before the contact with the scourtins (and thus by reducing the disadvantages related to fermentation inside the fibrous mass) for the systems in coupling with presses. Appearance of the decanters 2 phases to strongly reduced the interest of this device relatively slow and difficult to clean.

Separation of oil and water

Other than the method of Sinolea, the oil must obtained by the extraction always contains a residual quantity of water which is then eliminated by the effect of the difference of Densité between the two liquids by the Décantation or centrifugation.

Natural decantation

It is the old method founded on not-miscibility of oil and water. In phase of rest, oil, lighter, tends to go back to surface, while separating from water. Must, hardly resulting from pressing, undergoes the first separation which makes it possible to obtain a product of better quality. The separation of the residual quantity required on the other hand a longer decantation in the oilcan in cemented vats envisaged for this purpose. In a similar way, one recovered a quantity of residual oil of bad quality starting from the margines stored in the hells, a room envisaged for this purpose.

The natural decantation is a strongly forsaken method owing to the fact that it is very difficult to exploit within the framework of the current qualitative requirements.

Vertical centrifugation

Vertical centrifugation is the system employed in all the installations to separate oil from water. One subjects to this process either oil must obtained by pressing or horizontal centrifugation, or the water of vegetation resulting from horizontal centrifugation.

For this purpose, one uses vertical centrifugal separating . They are machines borrowed from the installations of the milk industry (separators) which carry out separation under the terms of a rotation at high speed. The centrifugal separator consists of a cylindrical tank containing the revolving drum composed of a series of conical plates perforated and superimposed. The oil must, introduced by the top enters the drum and is subjected to a centrifugation with 6000-7000 turns per minute. Under the effect of the difference in density, oil and water separate into two flow different. During rotation, it occurs an accumulation of solid residues which are expelled via an automated security system (washing).

Secondary treatments

On the outlet side of the separator centrifuges, oil is a product ready with consumption. Such as it is, this oil still contains solid residues in suspension (Mucilage S and grease S) and presents a turbid aspect. With at-rest state, the solid residue settles on the bottom of the container and oil is clarified spontaneously. Consequently, as of its exit of the separator, oil is preserved in steel tanks, under an atmosphere of Azote to prevent oxidation and to support the spontaneous sedimentation of the dregs. The oil intended for an immediate marketing on the other hand is subjected to a filtration using cellulose filters of the type barese or filter presses before the setting in bottles.

Evacuation of the rejections of oil mill

One of the main issues of the management of the mills with oil is the elimination of the Margines. This by-product is an effluent which has a polluting load because of its content of Organic matter (of which chemical oxidation or biological tiny room content of Oxygène of surface waters) and especially by its excessive content of phenolic compounds (of which the biodeterioration is low).

In Italy, one admitted in the past the discharge of the margines directly in the sewers, but following the application of the law n° 319 of 1976 (known under the name of Loi Merli ), the effluents of the industrial activities which do not satisfy one or more parameters can be poured in surface waters only after one treatment which reduces the polluting load of it. In the years 1980, the mills with oil profited from exemptions to allow the scientific research the settling of methods of acceptable treatment and spreading on the economic plan. The technical solutions, indeed, were and remain still inapplicable in the context of the Italian olive-growing sector, characterized by the small size of the mills which are not able to carry out the economies of scale necessary to support the costs of a purifying plant. The rigorous application of the law would have, in fact, trained the closing of the majority of the Italian mills with oil.

For this reason, one applied in second half of the years 1980 a mode of exemption which allowed the spreading of the oily effluents on arable lands. Meanwhile, it appeared that the environmental impact of the spreading of the margines is much weaker than that of their discharge in surface waters, with the proviso of not exceeding certain thresholds according to the duration and of surface, especially to avoid the pollution of the ground water.

The margines épandues on the ground have, at the beginning, an effect cleaning on the bad grasses and slightly antibiotic by the action of phenols. To that, atmospheric pollution because of the bad smells exhaled by the effluents of oil mills is added. After one period from 5 to 6 months, appear the positive effects related to the humification and on the grounds which received margines the plants show a greater vegetative strength due to the fertilizing action of these effluents.