Press release 4
How Olive Oil is produced: from the olive to the oil
Extraction techniques from its origins to present day methods
How to press olives: people have wondered how to do this since time immemorial.
Originally, olives were simply ground using a mortar, sometimes adding some hot water to aid the separation of the oil and the final yield. The crushed olives were then placed in a sack to which two sticks were attached to the edges; by simply rotating the sticks the olives were crushed further and the oil released, just like twisting a wet cloth to remove excess water.
However the first real revolution in pressing techniques was the invention of the rotating olive press: a large cylindrical stone (millstone) which was fitted with a wooden board and operated by hand or with the help of animals.
The application of the principles of the lever press allowed for further improvements in the yield produced. The olives, which were previously crushed and then placed in bags, were instead placed under a pole which had large stone weights attached to one end. In this way the olives were crushed as if they were in a large nutcracker thereby allowing the precious juices to flow freely. Refinements of this technique saw the substitution of the stone weights with a cord system using a winch system.
However the real invention to revolutionise the process was Archimedes’ Screw. Applying pressure on the end of the lever and then subsequently on the screw allowed for a level of pressure which was previously unthinkable. Such presses were constructed in larger and larger versions where the screw was operated with poles which were initially pushed by hand and then moved by ropes anchored to a vertical axis (gearbox), which allowed for further rotation of the press. One obvious evolution was the replacement of the wooden screws with similar structures in iron.
In 1830, a French agronomist, Pietro Ravanas, applied a revolutionary invention following Pascal’s law of communicating vessels thereby effectively creating the first hydraulic presses which were widely used in the region of Puglia, in particular in Bitonto.
The spread of electricity in the early years of the last century allowed for a considerable improvement in the efficiency of the systems, but the basic method of oil extraction remained that of traditional ‘pressure’. It was only in the 70s that a totally new extraction system was diffused: the centrifugal method. After the pressing, the olive paste is then placed in a large horizontal centrifuge (or decanter) which separates the oil from water and pomace.
Comparison of Extraction Processes: traditional and modern methods
This is the traditional method which has evolved over thousands of years as a result of the inventiveness of mankind and which still elicits the idea of authenticity, craftsmanship and quality.
Today this method is no longer able to adequately meet the needs of quality, hygiene and safety required in modern extraction processes however the technique is still practiced by many small-scale producers as they believe it enhances the concept of ‘naturalness’ regarding their products.
In this extraction process the olive paste extracted from the olives is directly separated by centrifugation into its components; oil, water and pomace. The method has evolved and been perfected over the last few decades and it is deservedly supplanting traditional systems based on pressure.
1. DEFOLIATION AND WASHING THE OLIVES
Both operations are performed infrequently. It is generally considered sufficient to eliminate the larger branches and wash any olives which have fallen to the ground.
Defoliation and washing the olives are absolutely necessary as the eventual presence of branches, stones, sand or dirt could damage the extraction plant.
Defoliation is performed using a suction process when the olives are placed into specific washing containers. Washing is performed by hydro-pneumatic machines and takes place in the water baths using forced water circulation.
2. OLIVE CRUSHING
Warning! Oxidation begins when the olive paste comes into contact with air.
The ‘mill or grinder’ is composed of a large granite base in the shape of a truncated cone which is hollow inside. In it, two large granite wheels (mill stones) are placed perpendicularly to the base and anchored to a central axis with two or three arms.
By slowly turning the millstones the olives are crushed along with their core to produce the olive paste. Appropriate ‘scrapers’ constantly convey the olive paste towards the wheels so as to optimize the crushing.
Modern centrifugal plants may also use the concept of ‘mills or grinders’ in the pressing phase however innovative systems have been introduced which are increasingly efficient. The crushers mainly consist of metal parts that allow for easy cleaning and high hygiene standards. Rotating at high speed, they instantly crush the olives, reducing them to a smooth paste. This modern technology of pressing, with respect to the traditional method, ensures that the olive paste is exposed to oxygen for a shorter period, thereby reducing the chance of oxidation, and allowing for greater efficiency within the process.
Warning! In any food production process, maximum attention must be given to hygiene and the cleanliness of instruments and machinery is fundamental.
‘Kneading’ is the slow mixing of the olive paste that has a dual purpose of breaking down the water / oil contents and also promoting the unification of the oil droplets into ever larger sizes, thereby preparing the paste for the subsequent separation phase of the oil.
In the plants used for kneading, part of the process is already undertaken during the crushing phase; induced by the continuous movement of the grinders. Subsequently, the olive paste is conveyed in a container fitted with blades which continue to turn the olive paste. Annexed to the kneading machine there is a ‘dispenser’, composed of a rotating circular base on which special discs of woven nylon fibre are arranged where a uniform layer of the olive paste is then distributed
Instant pressing of the olives with modern crushers creates a higher level of emulsions and therefore requires a more thorough kneading phase.
As a result the olive paste is conveyed in kneaders, semi-cylindrical containers provided with an axle on which tapes of helical rotating steel are fixed that slowly stir the olive paste.
Water is circulated between the kneaders, slightly warmed to 27-30 ° C, which facilitates the process.
4. CENTRIFUGE OF OLIVE PASTE
Warning! Only centrifugation allows for an effective separation of the water from the oil.
At this point, the ‘tower’ of discs is placed under the hydraulic press. Here pressure is applied, sometimes at a level greater than 400 atmospheres, which squeezes out all the remaining liquid components of the olive paste, that is to say the vegetal liquids and the oil.
The heart of the modern extraction process consists of a powerful horizontal centrifuge or ‘decanter’. The strong centrifugal accelerations that develop, allow for the separation of the olive paste directly into the three components in different specific weights: water, oil and olive pomace.
5. FINISHING SEPARATION
Warning! The persistence of large quantities of water in the oil accelerates the fermentation process
Before centrifuges were introduced, the oil was separated from the vegetal water by using the process of natural settling. However this process is slow and does not allow for the complete separation of the components.
In addition, exposure to air and the residue of large quantities of water in the oil accelerates the processes of oxidation and fermentation. Nowadays, centrifugal separators are used to ensure the quick and efficient separation of oil from the vegetal water.
On leaving the decanter the oil is conveyed into a centrifugal separator which has the purpose of removing further vegetal water present in suspension, thus obtaining a product with lower moisture and improving stability during storage. The vegetal water residue is also directed to a different separator with the aim of recovering any traces of oil in order to ensure the perfect efficiency of the whole process also in terms of oil yield.