Olive oil extraction is the process of extracting the oil present in the olive drupes for food use. The oil is produced in the mesocarp cells, and stored in a particular type of vacuole called a lipovacuole. Every cell contains a tiny olive oil droplet. Olive oil extraction is the process of separating the oil from the other fruit contents. After washing the olives different known techniques may be employed for extracting oil. Traditional methods typically press the olive using a grinder with two millstones. First the olives are ground into an olive paste using large millstones. The olive paste is generally ground by the stones for 30 to 40 minutes for guaranteeing that the olives are well ground and for allowing the fruit enzymes to produce some of the oil aromas and taste. After grinding, the olive paste is spread on fiber disks, which are stacked on top of each other, then placed into a press. These disks 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. To facilitate separation of the liquid phases, water flows on the sides of the disks to increase the speed of percolation. The liquids are then separated either by a standard process of decantation by gravity or by means of a faster vertical centrifuge. The traditional method provides good results and high quality of oil, although the machine is rather difficult to clean. It is a non continuous process with waiting periods thus exposing the olive paste to the action of oxygen and light. This method typically requires additional manual labor and a longer time period from harvest to pressing as compared to other methods for producing olive oil.
Modern methods of olive oil extraction use an industrial decanter to separate all the phases by centrifugation. In this method the olives are first crushed to a fine paste. This can be done by a hammer crusher, disc crusher or knife crusher. The paste is then malaxed for 30 to 40 minutes in order to allow the small olive droplets to agglomerate. The aromas are created in these two steps through the action of fruit enzymes. Water is added to facilitate the extraction process with the paste during malaxation. Typically the added water is heated in order to produce higher extraction percentage of olive oil. However, water temperatures above 35 degrees Celsius adversely affect the quality of the produced oil. Afterwards the paste is pumped into an industrial decanter where the phases are separated. The decanter is a large capacity horizontal centrifuge rotating at approximately 3000 rpm. The high centrifugal force created allows the phases to be readily separated according to their different densities (solids>vegetable water>oil). Although this technique is continuous and automatic providing high percentages of oil extraction it still produces large amounts of vegetable water to be disposed of and a reduced amount of antioxidants due to the added water.
Yet another known method for extracting oil, also know as “Sinolea” is a process which employs rows of metal discs or plates which are dipped into the paste. The oil preferentially wets and sticks to the metal and is removed with scrapers in a continuous process. The method is based on the different surface tension of the vegetable water and the oil; these different physical behaviors allow the olive oil to adhere to the steel surface while the other two phases stay behind. However large surface areas can lead to rapid oxidation of the olive product. In addition, the cleaning process of the surfaces is difficult and time consuming.
All above methods are designed for large scale industrial press applications and for handling of large quantities of olives and oil.
There is hence a long need for a system and method for extracting oil which may also be used as a house hold counter-top appliance. Such desired method may not require any additives nor trained personnel.