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There are several methods used to produce virgin olive oil. These range from the most traditional systems, which use a stone mill, hydraulic presses and natural decantation in settling tanks, to the most modern technology based on the two-phase centrifugation process. All of these methods have one thing in common: they use only mechanical and physical processes.
Below we explain the stages involved in producing virgin olive oil using the two-phase extraction system, the most advanced process currently available and the one we use at Las Valdesas.
The olives arrive at the olive mill, where the first step is to remove any leaves collected during harvesting. The olives pass through an air separator, where a stream of air blows the leaves away. These leaves are then used to produce compost.
If the olives are covered with mud or dust, they are washed in an industrial washing machine before processing. Finally, they are weighed and conveyed to the milling stage.
During this stage, the olives are crushed to produce an olive paste. This is carried out using a hammer mill, in which high-speed rotating hammers force the olives through a screen with openings typically between 3 and 5 mm. By selecting different screen sizes, the miller can produce a coarser or finer olive paste.
In our opinion, malaxation is one of the least well-known stages in olive oil production. After crushing, the olive paste contains between 15% and 20% olive oil. The remainder consists of water, fragments of olive stone and solid vegetable matter.
The challenge is that the olive oil is dispersed throughout the paste in tiny droplets, making it difficult to separate. During malaxation, these small droplets gradually combine to form larger ones that can be extracted more efficiently.
This process takes place in stainless-steel malaxers fitted with slow-moving paddles that gently mix the olive paste.
The malaxers are surrounded by a jacket through which warm water circulates, allowing the temperature of the paste to be carefully controlled. Higher temperatures reduce the viscosity of the oil, making it easier for the droplets to combine. However, excessive heat also reduces the oil's aromas and flavours. For this reason, the highest-quality extra virgin olive oils are produced by cold extraction (What is cold-extracted olive oil?). During malaxation, the temperature is typically maintained between 25 °C and 35 °C.
Malaxation is therefore one of the most important stages in olive oil production. The miller carefully controls both the temperature and the duration of the process, which typically lasts between 30 and 60 minutes.
Once the olive paste has been prepared, the extraction stage begins. This is carried out in a horizontal centrifuge commonly known as a decanter centrifuge. The process separates the different components of the olive paste according to their density. Olive oil is the least dense component, followed by vegetation water, while the solid residues, including fragments of olive stone and pulp, are the heaviest.
The decanter consists of a horizontal cylindrical drum that rotates at approximately 4,000 rpm. The centrifugal force pushes the heavier components towards the outer wall of the drum, while the lighter olive oil remains closer to the centre. As the olive paste moves through the machine, the different phases are separated and discharged through dedicated outlets.
Although the decanter separates most of the solid material, the extracted olive oil may still contain tiny particles of olive pulp and small amounts of water. These are removed using a vertical centrifuge.
During this stage, a small quantity of water is added while the oil is spun at high speed. Thanks to the difference in density, the water carries away the remaining solid particles and impurities. Once this final cleaning stage has been completed, the olive oil is transferred to stainless-steel storage tanks.
The olive oil is stored in stainless-steel tanks under an inert atmosphere to protect it from oxidation. Even after vertical centrifugation, the oil still contains tiny amounts of water and microscopic vegetable particles, which gradually settle to the bottom of the tanks through natural decantation.
Most olive mills filter their olive oil immediately before bottling. Filtration gives the oil a bright, clear appearance and prevents natural sediments from forming in the bottle.
Other producers filter the oil immediately after vertical centrifugation or a few days later. At Las Valdesas, however, we prefer not to filter our olive oils, allowing them to clarify naturally through decantation, both in our storage tanks and, over time, in the bottle itself.