Olive Oil production methodsHISTORICAL NOTES
The cultivation of olive trees and the production of olive oil developed in parallel with the evolution of the earliest civilizations in the history of mankind. In the VIII century B.C. the Greeks and Phoenicians started colonizing the western areas of the Mediterranean where they probably found olive trees growing wild. The Romans spread and developed the cultivation of olive trees throughout the empire and the Arabs improved the processing techniques. In past centuries, rural production sites were divided into three different areas: a storage area, a housing area for the "trapetum" and the "torculum" and a water and oil collecting area, equipped with two different tanks. A typical “trapetum” is similar to a present-day grindstone crusher.
In the course of time pressing systems improved, from the introduction of cage and column presses up to the general use of electrically powered hydraulic systems that replaced human or animal power. The production capacity of grindstone crushers is very limited, compared to their considerable size, and this system operates with a discontinuous cycle. The processing cycle begins with the leaves removing and olives washing operations, both essential to guarantee quality and hygiene to the oil produced, even though with this method the grindstones only partially break the leaves and so their influence on the final product is low.
The next stage of paste kneading prepares the paste for the separation of the oil by pressure. The stay time combined with heating of the paste, if required, becomes fundamental in order to avoid oil- water emulsion which would hinder the correct separation of the oil. The paste is then distributed on disks and stacked on the hand-trucks. Due to the strong pressure, the liquids (oil and water) are discharged out of the disks, while the solid residues (husks), with a very low oil and water content, are retained inside the disks. The final separation of the oil from the water currently takes place in a centrifugal disk separator which separates the oil ready for consumption from the waste vegetable water. The traditional system is a simple process, does not require process water (apart from a minimum quantity destined to the washing operation), produces very dry husks, operates with low power consumption, but requires a lot of manpower. The quality of the oil produced depends essentially on the correct use of the grindstones and of the disks, which are very difficult to clean. Bad cleaning can lead to the absorption and transmission of ffavours and odours, more or less pleasant, from one batch of olives to another.
Around the 1950s the hydro-pneumatic press was replaced by a system of extraction by centrifugal, using a horizontal centrifuge well known as “decanter". The Company VERACI, located in Florence, introduced the “PRIMOLIA ® ” onto the market, a discontinuous cylindrical basket centrifuge, with intermittent automatic discharge able to separate oil, water and solids. At the end of the 1960s Pieralisi transformed the “Primolia ® ” system into the first modern centrifugal continuous extraction system. This success was the result of years of research and represented a considerable progress compared with the system by pressing, ue to costs and manpower saving. The Pieralisi continuous system, which has been operating with great success on the international market for over half a century, is a combination of machines coordinated into a homogeneous, rational and technologically advanced production line. For the crushing of the olives the continuous system uses metal crushers equipped with a high-speed rotating body. Inside the crushers, the olives are crushed in different ways, creating deep breaks into the cells containing oil and ensuring very good centrifugal separation results with satisfactory yields. The more violent is the crushing of the olives, the deeper will be the breaking of the oil cells, with the result of a higher yield in oil and in minor components content (e.g. polyphenols). The crushing method which foresees the use of metal crushers ensures the best preparation of the olive paste destined to the decanter, after the kneading operation, for the extraction of oil using the two or three phase method.