Extracting oil from the fruit of the olive tree is a complex process but simply put: harvest the olives at the right time, gently wash & crush into paste, separate liquid from the solids, filter.
While traditional mills are still widely used, the sector’s continued efforts to achieve the optimal organoleptic characteristics and health properties have seen the technology used to produce olive oil change rapidly. Today, highly sophisticated electronically-controlled milling equipment quickly replaces the large stone grinders used for centuries to crush olive drupes.
It’s important to note that when olives are harvested to make extra virgin olive oil, they are taken from the tree to the mill in hours while still green and fresh and hard and never left to ripen on the ground or anywhere for any length of time.
Step ONE: Crush the Fruit
Once the olives reach the mill, the leaves left over from the harvest are mechanically removed, and the fruits are washed.
In traditional mills, olives are crushed with a procedure substantially unchanged for centuries: heavy grinders attached to a central column crush the fruits. Modern mills use advanced machines with hammer breakers, blades or rotary disks, allowing for a quicker transformation of significantly larger amounts of olives. Additionally, these tools greatly limit the exposition of the olives to oxygen compared to traditional methods, preserving their healthy and organoleptic properties.
Both crushing methods result in a raw olive paste made of the peel of the fruit, its pulp and fragmented pits. The paste also contains small olive oil drops and water, which is naturally contained in the olive drupes as they develop on the tree. This is one of the most delicate steps in olive oil making. Millers must take into account the temperature (should not exceed 20 ºC) of the olives themselves as they reach the mill.
The incorporation of state-of-the-art technology has paved the way for the increasing quality of olive oil production. Successfully producing the highest-quality olive oil heavily depends on agronomics, technology and the experience of trained technicians.
Step Two: Knead the Olive Paste
In a modern mill, the freshly-produced raw paste is transferred into the kneader, also called a malaxer.
The kneader is a tank equipped with blades that slowly stir the paste. The stirring process allows the blades to break up the water-oil emulsions created by the crushing. This process allows larger drops of olive oil to form, easing their separation from water, a crucial advantage for the final extraction.
For the delicate process to succeed, the olive paste is gently warmed but should not exceed 25 ºC. The temperature is considered the perfect balance between protecting the best qualities of olive oil and the production needs.
Kneading completion times vary significantly depending on the type of machines being used, the amount of olives, their stage of ripeness and the production goals in terms of quantity and quality but generally the shorter the time, the better to produce high quality EVOO.
Step Three: Extraction
In traditional mills, the raw paste is not subjected to kneading. Instead, it is carefully spread onto circular discs with a hole at the center. Piles of these discs are slowly pressed together, separating the oil and water from the pulp, which remains on the discs.
Given the goals of high-quality production, modern olive milling has adopted new means of extraction, no longer based on pressing. Oil extraction is now done with a decanter, or centrifuge, which spins very quickly to separate the oil in the paste from the water and pulp. Finally, the separated olive oil is transferred from the decanter into steel containers.
Depending on the machines’ specifics, olive oil coming out of the decanter might still contain traces of pulp, air or water. Filtering equipment is often used to speed up a natural process that would separate the olive oil from those particles, obtaining olive oil ready to be bottled and consumed.