What is cold pressing of olive oil?Oil’s cold pressing is the system used to extract the juice from olives, by separating oil and water that compose them. The extraction takes place, as the name suggests, using pressure. Once the olive has been harvested, it is crushed and kneaded to obtain a product known as “olive paste”. An oil with the “extra virgin olive oil” (EVOO) denomination must be extracted from the olive paste using only mechanical means (centrifuge machines), since the hot extraction process is the one used to get refined oils.
When an oil isn’t cold pressed?The oil makes up between 15% and 20% of the olive paste. Heating this paste at high temperatures would favours the oil particles concentration and, therefore, their extraction. However, above 27º C the oil loses its organoleptic properties (flavour and smell) as well as the benefits for the consumers health.
Oil extraction systems
Cold pressed, the traditional system.Traditionally, olive oil was obtained by introducing the olive paste between two mats made from esparto to which pressure was applied by metal plate means. The result of this process was a juice, made up of olive oil and water, which was allowed to flow into tanks where the oil was separated from the water by decantation. The different densities of water and oil made the latter occupy the upper part of the tank. However, this system became outdated due to:
- Hygienic-sanitary reasons, since current food regulations advised against the use of this system for obvious reasons.
- Economic reasons, since the yield was lower and the costs associated with its extraction made it extremely expensive.
- The esparto mats were requiring scrupulous cleaning after each use, since the organic remains that could accumulate in them were fermenting by bacterial action and transmitting smells and flavours to the new oil.
- Contact with the ambient oxygen and with the water obtained from the decantation was initiating the oxidation process much earlier which, again, reducing oil’s properties.
- This process was usually repeated two or three times, in order to obtain the maximum yield. This was making both the olive paste and the water start the fermentation process between each pressing, which was increasing oil degradation in each cycle.