In order to extract the precious oil from the mesocarp, or flesh cells, of the olive fruit, the extraction process naturally focuses on the separation of the oil and supplementary liquids from the solid material.

Washing the harvested olives with potable water and removing the leaves are the preliminary steps in this ancient process. The foreign material, if left, would adversely affect the flavor of the resulting product and damage the modern equipment that is currently used.

Crushing the olives with either stone mills or metal crushers produces a paste with easily extracted oil droplets within the resulting crushed substance. The older of the two methods is the use of stone crushers consisting of a stone base and upright millstones enclosed in a metal basin. There are usually scrapers to clean the millstones and paddles and blades to circulate and expel the paste. This process ensures that the paste is not overheated (which would adversely affect the flavor of the oil), the oil is
not contaminated with the metal and the emulsified paste produced is easy to extract. Due to the consistency and texture of the paste that this process produces, stone crushed olive oil is usually combined with pressing, although sometimes centrifugation is used. The difficulties associated with
this process are the slowness of the bulky machinery, the cost and the fact that the equipment cannot be continuously operated.

Metal crushers rotate at high speed throwing the olives against a metal grating. The oil is usually extracted from the paste by continuous centrifugation. The advantages include speed, continuous operation, low cost and high output. The primary disadvantages include the likelihood for metal
contamination and high temperatures which damage the flavor of the oil. In addition, this process produces a paste which contains smaller droplets of oil, more emulsified, and therefore harder to extract.

Mixing or beating the paste prepares the paste for separation of the oil from the pomace. This part of the process is important if the paste was made from metal crushers. This process will maximize the amount of oil to be extracted from the paste by breaking up the oil/water emulsion and forming
larger oil droplets. (If the speed, time and temperature devoted to the process are miscalculated, a stronger emulsion with oil more difficult to extract will result.) 

Extraction of the "liquid gold" is accomplished by pressing, percolation or centrifugation. Pressing is the oldest and most common method of oil extraction by applying pressure to stacked mats, smeared with paste, that alternate with metal disks. The oil is then expressed through a central spike. The advantages of this method include the use of simple, reliable machinery and little initial investment; the low energy requirement; a resulting pomace that is low in moisture/liquid content and precious little oil is lost to the water component. The disadvantages include a high labor intensity and the production is, therefore, not continuous.

Percolation incorporates the use of a metal plate dipped into the mixed paste which in theory becomes wetted with oil, and not with oil mixed with water, when withdrawn. The oil then drips off the plate. The disadvantage of this process is that it is inefficient because the wet pomace remaining still contains a great deal of olive oil. That is why the percolation process, if used at all, is usually combined with another process such as pressing or centrifugation, discussed below; however, the high initial cost and energy requirements, the resulting wet pomace and a high amount of remaining olive oil still attached to water make this procedure less than ideal.

Centrifugation uses high-speed centrifuges that extract the oil from the beaten paste through a fine screen. The advantages include speed of process, efficient and compact equipment/machinery and low labor requirement. The disadvantages include a high investment cost for equipment and trained ersonnel, high energy requirements, a pomace with a high moisture content and lost oil still attached to the water.

The three methods produce oil must and pomace. The oil must consists of edible olive oil and vegetable water. Centrifugal decanting is used to separate the oil from the water with the help of the naturally different densities of these liquids. Concentric spinning tanks pull off the oil, and the vegetable water drains into lower tanks.

The "waste" consists of solid and liquid waste. The solid waste uses include: 

1. Fuel

2. Fertilizer/Mulch

3. Herbicide

4. Animal Feed

5. Road Construction Material

6. Olive Bricks

7. Worm Breeding Material.

The most exciting use is fuel due to the extremely high cost of energy sources around the world. In Jordan, the primary use of pressing waste is fuel to heat households and power kilns. If completely dried, the solid waste is pressed into logs for burning yielding  extremely intense burning and an aromatic scent. Commercially sold charcoal consists in part of dried solid olive waste. This fuel source is environmentally non-polluting and biodegradable. The Turkish Daily News recently reported that Selcuk Gida has applied to the Energy Ministry for permission to produce energy from the olive oil cake. This kind of energy production would be a first in Turkey. The energy power station will cost $20 million and be established in Aydin's Germencik district. Sixty percent of the energy will be sold to Turkey Electric Distributing Company (TEDAS). The company Selcuk Gida is known to consumers of dried fruit which is sold under the Eagle Brand.

As a component of fertilizer and mulch, the olive waste should be mixed with soil and bark and should not be concentrated over the olive tree roots because the roots may burn. Usually, the olive waste is distributed around an orchard or farm and it serves as a natural herbicide, discouraging grass and weed growth. Some American farmers have reported the emergence of red clover where previously none existed. Red clover is a dynamic accumulator of nitrogen and phosphorous, and the presence of red clover (trifolium protense) is also an indicator of potassium.

This olive residue material is also a component of feed for animals such as cattle and poultry; however, goats and sheep eat it "straight" separating the edible portion from the woody parts. Americans use tons of the olive waste mixed with bitumen as a component of road construction material. Olive bricks, although lighter than traditional bricks, are also created from this solid residue as well as breeding material for worm breeding farms.

The chemical analysis of the solid waste consists of: 

The liquid waste water, according to ancient Roman texts, was used as a herbicide and insecticide. Modern research, however, has not yet uncovered viable uses to which this waste can be put. On the contrary, science has warned against depositing this substance into lakes, rivers or the sea due to the polyphenol. The acidity renders an excess of this waste water phytotoxic which can result in pollution.

Constantine Alexander
Certified Olive Oil Consultant