• Centrifugation^[8]: The mechanical process of separating oil from water and solid impurities by utilising centrifugal force. How it works: after cold pressing and malaxation, the olive paste that is left contains oil, water, and solids such as pulp or pit pieces, which are separated based on their density from oil using high-speed spinning. It is a rapid and continuous separation process while achieving optimal oil extraction, and with minimal labour requirements as it is fully automated. It can take place before or after the decantation process:
• Decanter centrifuges: The olive paste is separated from impurities and water when introduced into the decantation container (decanter) through a horizontal cylinder spinning at 3000-4000 rpm (revolutions per minute).
• Vertical centrifuges: Once decantation is done, the oil is processed in vertical centrifuges spinning at high speeds (6000 rpm).
• Cold pressing^[9]: It is a mechanical method used for extracting olive oil at temperatures below 27°C (80.6 °F). This way, the oil retains its quality and valuable substances (antioxidants, polyphenols). The method preserves oil’s natural flavor and is a staple for producing extra virgin olive oil. Although the method is often referred to as “cold extraction”, it’s not the same thing as either:
• Cold extraction that relies on centrifugation systems can affect the oil’s overall quality, or
• Cold-pressed extraction that uses a hydraulic press, which allows the oil to retain valuable properties.

Image 6 – Cold-pressed extraction – Source: Freepik.com

• Decantation^[10]: It is the natural process of clarifying oil from water or foreign bodies. The oil is left to rest (for days or weeks) in stainless steel containers with a conical bottom, allowing denser particles to settle at the underside. The fact that it doesn’t use any filters for separation leads to smaller particles of impurities being left. Therefore, although the oil is edible, it is better to be consumed within a few months of production as the residual solids may ferment over time.
• Filtration^[11]: It has a similar functionality to decantation, but it differs in its methodology as it involves passing the oil through various filter media, such as paper or cellulose filters, to remove water or impurities. Filtered oil is visually clearer than unfiltered oil, which may appear cloudy and has a longer shelf life. Regardless, the process might affect olive oil’s quality and distinctive taste by removing certain natural compounds.

Image 7 – Olive oil filtration – Source: Freepik.com

• Malaxation^[12]: This term refers to the slow mixing/churning of olive paste after cold pressing that lasts 20-45 minutes while it is heated up to 27 °C. It is a necessary process as it aggregates small oil droplets into larger ones, enhancing oil extraction efficiency. If performed for more than 45 minutes or using temperatures above 27 °C in heating, it can lead to oil oxidation and therefore affect the overall taste, aromas, and quality of the oil. Therefore, finding the optimal balance between mixing/churning time and heating temperature is very important to ensure that delicate aromas, antioxidants, and flavours are protected.

Image 8 – Steel containers with olive oil – Source: Freepik.com

• Ultrasound extraction^[13]: It involves using high-frequency sound waves to enhance the extraction process, leading to higher yields, improved quality, and faster extraction times.