Extraction

CLEANING THE OLIVES

The first step in the oil extraction process is cleaning the olives and removing the stems, leaves, twigs, and other remaining debris .  The olives should be washed with water to remove pesticides, dirt, etc.  Stones and sand will damage a hammermill and quickly wear out a centrifugal decanter or oil separator, reducing life span from 25 to as little as 5 years. It is amazing, and sometimes entertaining, to see what can be found in the bins with the olives.  Light contaminants are removed by a heavy air flow (blower) and heavy objects sink in the water bath.

GRINDING THE OLIVES INTO A PASTE
The second step is crushing the olives into a paste. The purpose of crushing is to tear the flesh cells to facilitate the release of the oil from the vacuoles.  This step can be done with stone mills, metal tooth grinders or various kinds of hammermills.  

MALAXING THE PASTE

Malaxing (mixing) the paste for 20 to 45 minutes allows small oil droplets to combine into bigger ones.  It is an indispensable step.  The mixer used is a horizontal trough with spiral mixing blades. Longer mixing times increase oil yield but allows a longer oxidation period which decreases shelf life.

SEPARATING THE OIL FROM THE VEGETABLE WATER AND SOLIDS

The next step consists of separating the oil from the rest of the olive components.  It is done by centrifugation, except in old facilities. Some centrifuges are called 'three-phase' because they separate the oil, the water, and the solids separately.  The two-phase centrifuges separate the oil from a wet paste.  In most cases, the oil coming out of the first centrifuge is further processed to eliminate any remaining water and solids by a second centrifuge that rotates faster.  The oil is then left in tanks or barrels where a final separation, if needed, happens through gravity.  This is called racking the oil.  Finally the oil can be filtered, if desired.