Olive oil extraction
[4][note 1] 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.
It was then placed within frails (being no more than flexible, woven baskets made of thick fibrous material, usually of rushes, palm fronds, hemp or willow splints),[6][7] stacked one on top of the other, to which was applied a stone weight to release the oil from the pulp.
[8][9][10] The extracted liquid which is obtained consists of oil and vegetable water (amurca = watery lees) mixed together,[6] and runs off into a pit.
[5]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.
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.
To facilitate separation of the liquid phases, water is run down the sides of the discs to increase the speed of percolation.
A similar problem can affect the grindstones that, in order to assure perfect quality, also require cleaning after each usage.
[12] Inferior oil is produced from unripe olives that are stored for extended periods of time until they grow soft or begin to shrivel to become more fit for grinding.
Grindstones, while ancient in design, are a suitable way to grind olives, because this method breaks up the drupe's pulp while only slightly touching the nut and the skin.
In addition, in this extraction method, the introduction of water is minimal when compared to the modern one, thus reducing the washing-off of the polyphenols.
The exhausted paste, called pomace, has a low content of water, making it an easier residue to manage.
Advantages Disadvantages The modern method of olive oil extraction uses an industrial decanter to separate all the phases by centrifugation.
[17] Advantages Disadvantages The Sinolea method to extract oil from the olives was introduced in 1972;[18] in this process, rows of metal discs or plates are dipped into the paste; the oil preferentially wets and sticks to the metal and is removed with scrapers in a continuous process.
Sinolea works by continuously introducing several hundreds of steel plaques into the paste thus extracting the 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.
In addition, the chemical content of the polyphenols, antioxidants, and vitamins present in the oil is reduced by higher temperatures.
Some producers, in order to maximise product quality, choose to combine the traditional grinding method, the stone mill, with a modern decanter.
Because the use of the stone mill requires a loading and unloading phase, this extraction method is discontinuous, i.e., there are times when all the machinery is stopped, therefore it is generally not used on a large commercial scale, being applied only by small scale olive mills producing high quality 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.
