🌀 Malaxation

Malaxation is the slow, continuous mixing of olive paste in malaxers before the oil is separated from it. After crushing, part of the oil is broken up into very fine droplets; during mixing their membranes break down, and the droplets merge into larger ones that separate more easily from the water and solids. Compared with paste that has not been malaxed, about 5% more oil is obtained.

Malaxers are horizontal stainless-steel tanks with a paddle shaft and a water jacket for heating; usually several are installed in a row. The paddles turn slowly, at 20–30 revolutions per minute. The olive mill operator watches the paste temperature, speed, duration and additives, which are allowed only for difficult pastes. A 2023 review of studies recommends 30–40 minutes at 18–27 °C. After malaxation the paste goes into the decanter centrifuge.

Malaxation is called a “necessary evil”. The longer and warmer the paste is mixed, the more oil you get, but the fewer beneficial phenols: heat speeds up the enzymes that destroy them, and a long time lets hexanal accumulate. This is also when most of the oil's aromas form via the lipoxygenase pathway: at 25 °C and below pleasant “green” notes appear, at 35 °C and above unwanted odours.

Air matters too. At an industrial olive mill, when the oxygen in the malaxer was kept at about 4.4%, Picual oil had 10% more phenols, and when oxygen was also limited during crushing, 20% more. Aromas dropped by 10–20%, but the oil remained extra virgin. That is why some mills replace the air above the paste with nitrogen.

On the bottle. Under EU rules (Regulation 2022/2104), the phrase “cold extraction” may only appear on extra virgin and virgin olive oils obtained by centrifugation or percolation below 27 °C, which tells you the paste was mixed without strong heating. An oil that has kept more phenols tends to show sharper bitterness and pungency: a trait, not a flaw.