Malaxation
In olive oil extraction, malaxation (Latin malaxare, Greek μαλακος meaning "soft") is the action of slowly churning or mixing milled olives, typically for 20 to 40 minutes. The churning allows the smaller droplets of oil released by the milling process to aggregate and be more easily separated. The paste is normally heated to around 27 °C during this process. Oil yield is proportional to the temperature and mixing time. However, the use of higher temperatures and longer mixing times increases oxidation of the oil and therefore decreases shelf life, so a compromise must be struck. Also, the usage of higher temperatures does not allow for the labelling of the oil as "cold extracted", a term used widely as a marketing tactic, especially in the European Union.
It is now possible with newer equipment to use a blanket of inert gas such as nitrogen or carbon dioxide over the olive paste, which greatly reduces oxidation. This allows for an increased yield without compromising the quality of the oil.
After malaxation is complete, the paste is sent to a phase separator. Nearly all producers use a decanter centrifuge for this process. Traditionally the olive oil was separated from the paste using a large press that was either screwed down or weighted with rocks.