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Olive oil extraction is the process of extracting the olive oil present in olive . Olive oil is produced in the mesocarp plant cell, and stored in a particular type of vacuole called a lipo vacuole, i.e., every cell contains a tiny olive oil droplet. Olive oil extraction is the process of separating the oil from the other fruit contents (vegetative extract liquid and solid material). It is possible to attain this separation by physical means alone, i.e., oil and water do not mix, so they are relatively easy to separate. This contrasts with other Vegetable oil that are extracted with chemical solvents, generally hexane.F. D. Gunstone, Vegetable Oils in Food Technology: Composition, Properties, and Uses, 2002, CRC Press, 351 pages The first operation when extracting olive oil is washing the olives, to reduce the presence of , especially soil which can create a particular flavor effect called "soil taste".
Olive presses were traditionally built within walled structures.Columella, De Re Rustica (Book 1, chapter 6:18): "The press-rooms especially and the store-rooms for oil should be warm, because every liquid is thinned with heat and thickened by great cold; and if oil freezes, which seldom happens, it becomes rancid. But as it is natural heat that is wanted, arising from the climate and the exposure, there is no need of fire or flame, as the taste of oil is spoiled by smoke and soot. For this reason the pressing-room should be lighted from the southern side, so that we may not find it necessary to employ fires and lamps when the olives are being pressed." Traditional olive-presses consisted of a crushing basin which is a large, cylindrical millstone mounted by an upper milling-stone (crushing stone) used to grind the olives and their pits into a pulp.Mishnah ( Baba Bathra 4:5), which reads: "He that sells an olive-press has ipso facto sold therewith the lower millstone attached, and the upper milling-stone used, and the upright posts, but he has not sold the pressing boards used, nor the lever wheel (winch), nor the lever beam.""The lower millstone, etc." Translation here follows the interpretation of the Hebrew words = yam, and = memal, as explained by Mishnaic exegetes Hai Gaon (939–1038) on Mishnah ( Taharot 10:8); Maimonides on Mishnah Baba Bathra 4:5 and in his Mishne Torah (Hil. Mekhirah 25:7) as pointed out by Rabbi Vidal of Tolosa; and by Nathan ben Jehiel (1035–1106) in his Sefer ha-Arukh, s.v. ; Obadiah Bartenura in his commentary on Mishnah ( Maaserot 1:7), as well as by Moses Margolies (1715–1781) in his commentary P'nei Moshe on the Jerusalem Talmud ( Baba Bathra 4:5), and by Nissim of Gerona on Isaac Alfasi's commentary on Avodah Zarah 75a, among others. See also , s.v. Formerly, the upper milling-stone was rotated by a beast of burden harnessed to a wooden beam, or horizontal shaft, and which turned the crushing stone. The draft animal which rotated the horizontal shaft was always blindfolded to prevent it from getting dizzy. After which, the pulp was collected and kneaded. It was then placed within Basket (being no more than flexible, woven baskets made of thick fibrous material, usually of Juncaceae, palm fronds, hemp or willows), stacked one on top of the other, to which was applied a stone weight to release the oil from the pulp.The stone weight, which could be as much as 400 kg, was lifted by means of a Lever resting on a pivot (fulcrum) between two vertical posts. The extracted liquid which is obtained consists of oil and vegetable water ( amurca = watery lees) mixed together, and runs off into a pit. After settling, the oil rises to the surface and is removed by way of decantation. Filtering the oil produces a clearer batch of oil. The olive residue that remained was used for lighting fires.
About 50–70 kilograms (110–155 pounds) of olives were spread within the crushing basin and crushed for 30-50 minutes. Sometimes water would be added to facilitate the movement of the crushing stone. From time to time a worker would push the olives into the path of the moving stone with a spade-like tool.
The following basic method is still widely used today, and remains a valid way of producing high quality olive oil if adequate precautions are taken.
First the olives are ground into an olive paste using large at a corporate oil mill. The olive paste generally stays under the stones for 30–40 minutes. This has three objectives:
In modern-day mills, after grinding, the olive paste is spread on fibre discs, which are stacked on top of each other, then placed into the mechanical press. In modern times, these discs are made of synthetic fibres which are easier to clean and maintain.
These discs are then put on a hydraulic piston, forming a pile. Pressure is applied on the disks, thus compacting the solid phase of the olive paste and percolating the liquid phases (oil and vegetation water). The applied hydraulic pressure can go to 400 atm. To facilitate separation of the liquid phases, water is run down the sides of the discs to increase the speed of percolation. The liquids are then separated either by a standard process of decantation or by means of a faster vertical centrifuge.
The traditional method is a valid form of producing high-quality olive oil, if after each extraction the discs are properly cleaned from the remains of paste; if not the leftover paste will begin to ferment, thereby producing inconsistencies of flavors (called defects) that will contaminate the subsequently produced olive oil. A similar problem can affect the grindstones that, in order to assure perfect quality, also require cleaning after each usage.
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Afterwards the paste is pumped into an industrial decanter where the phases will be separated. Water is added to facilitate the extraction process with the paste.
The decanter is a large capacity horizontal centrifuge rotating approximately 3,000 rpm, the high centrifugal force created allows the phases to be readily separated according to their different densities (solids > vegetation water > oil). Inside the decanter's rotating conical drum there is a coil that rotates more slowly, pushing the solid materials out of the system.
The separated oil and vegetation water are then rerun through a vertical centrifuge, working around 6,000 rpm that will separate the small quantity of vegetation water still contained in oil and vice versa.
The two phases oil decanter was created as an attempt to solve these problems. Sacrificing part of its extraction capability, it uses less added water thus reducing the phenol washing. The olive paste is separated into two phases: oil and wet pomace. This type of decanter, instead of having three exits (oil, water, and solids), has only two. The water is expelled by the decanter coil together with the pomace, resulting in a wetter pomace that is much harder to process industrially. Many pomace oil extraction facilities refuse to work with these materials because the energy costs of drying the pomace for the hexane oil extraction often make the extraction process sub-economical. In practice, then, the two phases decanter solves the phenol washing problem but increases the residue management problem. This residue management problem has been reduced by the collection of this wetter pomace and being transported to specialized facilities called extractors which heat the pomace between 45 °C and 50 °C and can extract up to a further 2 litres per 100 kilos of pomace using adapted two-phase decanters.
The two-and-a-half-phase oil decanter is a compromise between the two previous types of decanters. It separates the olive paste into the standard three phases, but has a smaller need for added water and also a smaller vegetation water output. Therefore, the water content of the obtained pomace comes very close to that of the standard three-phase decanter, and the vegetation water output is relatively small, minimizing the residue management issues.
Depending on the olives and processing, the Decanter or Tricanter can extract between 85 and 90% of the olive oil in the 1st extraction. The yield from olive oil manufacture can be increased even further with a 2nd extraction. The olive oil yield increases to as much as 96% by combining the 1st and 2nd extractions. Higher Yield due to the 2nd Extraction in Olive Oil Manufacture
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Sinolea works by continuously introducing several hundreds of steel plaques into the paste thus extracting the olive oil. This process is not completely efficient leaving a large quantity of oil still in the paste, so the remaining paste has to be processed by the standard modern method (industrial decanter).
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In the EU, these designations are regulated by Article 5 of Commission Regulation (EC) No 1019/2002 of 13 June 2002 on marketing standards for olive oil. This article states that in order to use these designations the olive oil bottler must prove that the temperature of malaxation and extraction was under 27 °C (80 °F).
For olive oil bottled outside EU countries, this regulation does not apply, and thus the consumer has no assurance that these statements are true.
The temperature of malaxation and extraction is crucial due to its effect on olive oil quality. When high temperatures are applied, the more volatile aromas are lost and the rate of oil oxidation is increased, producing therefore lower quality oils. In addition, the chemical content of the polyphenols, antioxidants, and present in the oil is reduced by higher temperatures. The temperature is adjusted basically by controlling the temperature of the water added during these two steps. High temperatures are used to increase the yield of olive oil obtained from the paste.
The two main agents that cause the degradation of olive oil are oxygen and light. Once an olive is harvested, it should be pressed within 24 hours. Oxidation begins immediately upon harvesting. In the period between harvest and grinding, the fruits' enzymes are very active and increasingly degrade the endogenous oil, and therefore oil obtained after a longer wait is of lower quality, presenting higher acidity (free fatty acids percentage).
In addition, if additional oxygen is allowed to interact with the olive paste during the extraction process, the acidity level will increase further. Sealed extraction methods are best to prevent the continued introduction of oxygen, as well as light to the oil.
After extraction is complete, in most cases unfiltered olive oil appears somewhat cloudy, mainly due to the presence of minute amounts of water and suspended solids of olive pulp and seed. This type of oil is therefore sometimes called cloudy or veiled olive oil.
It is common practice that unfiltered olive oils are then "racked" for a time, i.e. stored in cool stainless steel silos with a conical bottom that are pumped free of oxygen to enable the precipitation and separation of the two phases and facilitate later filtration; it will also contribute in the integrity and stability of the oil.
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