The extraction of olive oil is an industrial process of agro-food processing, which has the purpose of extracting oil from the olive groves. Since antiquity, all peoples overlooked the Mediterranean, they knew the unique and extraordinary value of olive oil, which was already used as a fundamental dressing for various dishes on which the olive plant found Just conditions to spread; In addition, compared to other foods, oil has immediately captured the ancient populations even for the extreme simplicity of preparation. Today, the process has remained largely unchanged and, thanks to technology, techniques that have been passed down for centuries have been improved. This transformation, carried out in an oil mill structure (Milling), takes place in two fundamental phases: grinding the pulp (Milling or grinding) and subsequent separation of the oily fraction from the other components (Water-pomace). Italy is the second largest producer of olive oil in the world after Spain, and boasts a wealth of 533 varieties of olives and 43 oils protected by the European Union.
OLIVE OIL PRODUCTION PHASES
Modern technology has made great strides forward, so the machining lines used for the extraction of extra virgin olive oil. They differ from each other for the different applications used in the individual processing phases; Therefore, the common steps for all technologies are the following:
Olive harvesting takes into account the degree of ripening of the fruit, and of all its components, responsible for the final quality. In many areas traditional systems are hand-picked, always well-protected: yield is low and the most expensive operation. With the grinding, the amount of collected daily increases greatly, but also damage to the tree, if calculated for broken shoots. In countries where the cost of labor is higher and in those where it is more difficult to dispose of it at the moment and to the extent necessary, use of vibrators of branches or trunks, with damage to trees similar to those of manual collection, That is, very low. The detached olive is collected in synthetic fibers, light and large, placed under the trees. In certain areas with work-related problems other types of pickers are used: trailers with extensible nets and also special attachments mounted on the tractor. In recent years, the use of pneumatic combs has been increasingly popular, because, in addition to being cheaper than shakers, they allow a better defective organization of the collection phases. Mechanized harvesting is also progressively spreading through a system that involves the combined use of trunk vibrators with ground nets or other olfactory interceptor systems.
It consists of the cut of the olives to separate them from the ground, sprigs and leaves. Sorting on large matches is done using static screens or vibrating tapes. In the past it tended to leave a fair amount of foliage in order to give the oil the fruity taste.
It is carried out in the building at the moment of the assignment. The supply chain in Italy, mostly made up of small olive-growing companies that give the product to third-party oil mills, means that the quantities supplied are generally small. The weighing is then carried out after the discharge from the transport vehicle in cassettes, bins or sacks.
With small, hand-picked matches, this phase takes place partly in the olive grove in order to reach the sufficient quantity to be allocated for a working cycle. With large matches, usually obtained with mechanization systems, harvested olives are directly transferred to the mill and stored in a separate area or area or directly in a space in front of the processing line. In the past, olives were stored in jute bags, currently used for drilling or bins. The quality of the final product depends on the state of conservation of olives (In a well-ventilated environment) and the waiting times, in fact the ideal would be processed within 24 hours of harvesting. Unlike these conditions, the onset of olive oil fermentation processes results in inferior quality of the oil. This phenomenon is accentuated in the case of olives that have suffered trauma during collection or attacks by the oleaginous fly.
It is done by immersing the olives in a water tank or, in modern plants, in special washers that maintain forced water handling to improve the result of the operation. In order to obtain a quality oil at this stage, it is also important that the water used is clean and recycled frequently. At the end of the operation, the olives undergo a drying process by simply washing off the washing water, or only by means of air jets and conveyor belts.
The milling is the first phase of actual extraction. Olives are subjected to mechanical actions that cause the cellular wall and membrane breaks with the resulting leakage of cellular and oil juices. This action is entrusted to the rubbing of the core fragments on the pulps or to the impact of high speed rotating mechanical devices in the pulp mass. The product obtained from this stage in most plants is the oil pasta, consisting of a solid fraction (Fragments of olive stones, skins and pulp) and a liquid (Water-oil emulsion). The systems used are basically of two types:
– CLASSIC MILLING: The molasses are the traditionally used tool, conceptually derived from ancient stone mills: mechanical action is exerted by the rotation of one or more large stone wheels (Granite) on the working mass. The sucking of the juices is caused by the rubbing action of the sharp edges of the core fragments on the olive pulp. The function of the wheel is therefore to crush the kernels in the appropriate dimensions and to scramble the working mass. In the past, the molza consisted of a single wheel driven by an arm from a donkey or a horse, so it had a considerable volume to allow the animal’s circular movement. Current molasses (Slow rotation: 12-15 rpm for a total time ranging from 20 to 40 minutes) is driven by an electric motor and has smaller dimensions. It consists of a basin with a granite or steel base and raised steel edges and a system with 2-6 wheels with a horizontal stone axis (Granite), arranged in pairs at distances different from the vertical axis of the tank. The bumper of the wheels is raised a few millimeters from the bottom of the tank and is adjustable so as to obtain kernel fragments of adequate size. The molza is finally provided with blades that are designed to remove the paste that adheres to the wheels and improves stirring by pushing the pasta under the bark. The amount of olives processed in an average cycle is 2,5-3 quintals so as to obtain a sufficient amount of pasta to carry the load of a hydraulic press during the extraction step.
– PRESSING: The hammer mill is the preferred instrument in modern continuous cycle systems because it is perfectly integrated with the requirements of plant automation. The load is mechanically carried out from above, with belt elevators. The drainage takes place from the bottom, always mechanically, with the pouring of the oil paste into the grinders. A hammer crusher consists of a series of rotating disks with live edges (Hammer rotation speed 1200-3000 rpm). With this system the pulp rupture is caused by the collisions of high speed rotating devices and only partly by the mechanical action of the core fragments. The work is carried out in a very short time and the space is in the order of a few square meters
Gramming is a subsequent operation of the crushing and is intended to break the emulsion between water and oil and cause the oil micelles to flow into larger drops that tend to separate spontaneously from the water. It is carried out in said gram-or-brush machines. The grain is basically a steel tub, which rotates helical blades (20-30 rpm), keeping the oil paste in slow re-mixing. The resorption action breaks the emulsion and then improves the yield of oil in the subsequent extraction step. Current constructive typologies include several grams arranged in series or in parallel and loaded mechanically with the oil pasta exited by the franchise or molasses. There is also a type of gram-metering device provided with an oil pasta distribution system on the filtration diaphragms used in pressure extraction.
It consists in the separation of the oil from the sausage. The extraction is carried out with alternative systems that exploit different mechanical principles and characteristics according to the extraction method used. The extraction methods relate to three fundamental types:
– PRESSURE EXTRACTION: this is the classic method that separates the oil from the sausage through filtration by the effect of a pressure. The pressure takes place in an open hydraulic press, placing the oil pasta on thin layers alternating with filter diaphragms in a trolley tower. The device used for the construction of the stack consists of a circular steel plate with slightly raised and contoured shingles, shrouded for handling. At the center of the plate is inserted a perforated cylinder (Foratin), which aims to keep the stack in the vertical position and favor the flow of the oil must also along the center axis of the stack. The stack construction is done in a standard order: the filter diaphragm consists of a synthetic fiber (Nylon) disc centered in order to be threaded along the foratin. On the first diaphragm, placed on the bottom of the plate, there is a thick layer of 3 cm thick pasta, superimposed on a second diaphragm and a second layer of dough, and so on. Every three layers of dough overlap a non-plywood diaphragm and a steel disc, distributing evenly the pressure. A stack consists of the overlapping of 60 diaphragms alternating with 60 layers of pasta, 20 steel disks and 20 diaphrams without dough (Corresponding to a lot of molitous molasses with molasses (2,5-3 quintals) The entire load operation of a press was carried out by hand, but currently special dosers are used, often integrated with the grain. At this point the tower is inserted into the press and subjected to medium pressures of the order of 400 atm. The oil must separate from the solid fraction and the drainage system and flows along the outside and along the foratin and is collected on the plate. After the extraction, the battery is disassembled and the diaphragms are removed using special machines.
– CENTRIFUGATION EXTRACTION: The oil paste is subjected to a centrifugation (3000/3500 rpm) in a rotating conical drum with horizontal axis (Decanter). Due to the different specific weight, the centrifugation separates 2 or 3 phases. According to technical specifications, three basic types of decanter are distinguished. The 3-stage decanter is the oldest type and has several disadvantages. The centrifugation separates the sanse, the oil must (Containing a small amount of water) and the vegetation water (Containing a small amount of oil). This system requires prior dilution of the oil pasta with water, with high water consumption (The pasta washing action leads to the extraction of a high amount of polyphenols) and high amounts of vegetation water. The 2-Phase Decanter is the most recent typology and sums up the merits of the two different systems. Processing requires the addition of a small amount of water and separates three fractions (Sanse moisture, vegetable water, olive oil). The advantage of this system is that it produces a lower amount of vegetation waters and a lower pollutant charge. In both systems, sanse can not be given into the sanitizers because they are too moist to be processed.
– SINOLEA EXTRACTION: Sinolea is a device integrated into a continuous cycle plant that is based on a machining scheme different from other plants. The physical principle on which Sinolea is based, conceived since 1911, is the difference between the surface tension of vegetation water and that of oil: as a result of this difference, the oil tends to adhere easily to a metal surface compared with water, which is separated by percolation. The extraction method is also called selective filtration or filtration. The Sinolea consists basically in a tank containing the oil pasta, produced by a hammers whipper, in which the extractor device suffers. The latter consists of a series of several thousand steel blades that is immersed in oil pasta with a continuous alternate motion cycling through the following phases:
– Oil scraping.
At each dive cycle the lifting of the device dampens the vegetation water due to gravity while the oil adheres to the metal surfaces. The efficiency of the process is based on the high number of lamellas (About 5000), which is essential for a sufficient interface surface. The bike is pretty slow (7-9 rpm). During the return motion the metallic surfaces come into contact with a scraper device that removes the oil from entering into a collecting system. This system makes it possible to obtain a very high quality oil, yet it has a fairly low yield. If economic convenience exists, the residual pasta can be subjected to a second centrifugation extraction process. In this way you get two products differentiated in terms of quality. The advantages of the operational order consist of automation and, consequently, in perfect integration of the process into a continuous cycle of machining; The oil extracted from Sinolea* is also water-free and does not require the next centrifugal separation. In view of the aforementioned advantages, the disadvantages of low returns, the intrinsic aspect of this process, must be reported. The specific yield depends essentially on the quantity of water / oil present in the worked olives and may be less than 50% of the total theoretical amount. This forces the Sinolea to be coupled to a plant that allows extraction by centrifugation of the residual pasta, resulting in an increase in processing costs.
With the exception of the Sinolea method, the extracted oatmeal always contains a residual amount of water which is separated due to the different density of the two liquids by decanting or centrifuging:
– DECANTATION: This is the traditional method based on the non-miscibility of oil and water. During rest, the oil, being lighter, tends to surface on the surface, separating itself from the water. Once obtained with squeezing oil, the oil must undergo a first separation to obtain a higher quality product. The separation of the residual amount required instead longer periods of parking in the olives in special masonry tanks. Decanting is a completely abandoned method as it is unsuitable for obtaining quality products.
– VERTICAL CENTRIFUGATION: it is the system used in all systems (Except the oil extracted with Sinolea) to separate the oil from the water. The process is subjected to either the must obtained by squeezing or horizontal centrifugation, as well as the vegetation water obtained by horizontal centrifugation. Vertical centrifugal separators are used for this purpose. These are machines (Skimmers) that perform separation by virtue of high speed rotation. The centrifugal separator consists of a cylindrical reservoir containing the rotating drum consisting of a series of perforated and overlapped conical discs. The oil drops from the top into the drum and is subjected to a centrifugation (6000-6500 rpm). Due to the different oil-water density they separate into two different effluents. During rotation there is an accumulation of solid residues (Oil foots) which are ejected via an automated security system.
When leaving the centrifugal separator, the oil is cloudy. If the oil is immediately marketed, it is processed by special filters before packaging. Otherwise, it is stored in steel vessels in contact with a nitrogen atmosphere to prevent oxidation and exploit the spontaneous sedimentation of the mulch, favoring the clarity of the oil.
The information contained in the labels regarding the methods of extraction of olive oil is information that helps to understand the quality of the product. On this premise, it is good to specify that the production phases differ according to the technologies used; this, in order for the oil to be referred to as “Cold Extract” or “Hot Extract”, must be subject to the following conditions:
– “Cold Extract” olive oil is defined when during the extraction process it has not been subjected to temperatures above 27°C (The optimum temperature for cold extraction would be 25°C); however, it is good to specify the distinction between “Cold pressing of olives” and “Extract of a cold olives”:
1) “Cold pressing of olives” means a first mechanical squeezing of the pasta with the traditional hydraulic press system;
2) “Extract of a cold olives” means the percolation or centrifugation process of olives. So the difference lies in the 3-phase separation system (Oil-water-pomace).
– It is defined as “Hot extract” olive oil when it has been subjected to temperatures above 27°C (Hence even around 35°C to 40°C) during the extraction process in order to increase its yield, While altering the organoleptic properties and the chemical characteristics (Increasing sweet notes and decreasing fruity and vegetable odors) by using heat in the following phases:
1) Kneading: In this case there is an outer shirt with the function of increasing the temperature up to 40°C; The product overheating promotes the emulsion of the oil in the olive paste;
2) Extraction with decanter (Horizontal centrifugal extractor): At this stage the decanter develops temperatures around 40°C. In addition, some 3-stage decanter also use hot water, thus favoring the washing of polyphenols;
3) Washing presses for end spremiture: Hot water is used in this phase, affecting the finished product negatively.
OLIVE OIL TYPES
When it comes to olive oil, it is also necessary to define its own categories. They clearly identify how much they are buying and consuming. In any case, it is not so difficult to understand how olive oil is ranked. This chart helps to better understand the aspects of this subdivision:
After drying (To facilitate evaporation of the water contained therein), the olive slice can be subjected to further oil extraction by means of chemical treatments. Obviously, according to the extraction method used, the percentage of oil present in it varies from 3% to 6%.
**N.B. For mechanical extraction (Condition required for the production of virgin oils) means any process which leads to the production of oil from the olives and only and exclusively mechanical apparatus, excluding any form of extraction by chemical processes.