⚙️ Decanter centrifuge

A decanter centrifuge is a horizontal centrifuge that, at an olive mill, separates the oil from the water and solid residues of the olive paste. The bowl spins fast, heavier particles are thrown against its walls, and a screw conveyor inside carries them out continuously. The oil, as the lightest phase, comes out separately.

For centuries oil was pressed out with presses, and centrifuges appeared only in the early 1970s. Today continuous systems are used almost everywhere. A three-phase decanter needs added warm water and gives three streams: oil, pomace and wastewater. A two-phase decanter works without added water and gives oil and a single wet mass, pomace together with the fruit's juice, with 50–70 per cent moisture.

The oil depends on the type of decanter. Oils from two-phase decanters contain more phenolic compounds and resist oxidation longer, because water does not wash out the beneficial compounds. A study of 38 decanters in Catalonia showed that they recover 78–91 per cent of the oil and work best when loaded to 60–80 per cent.

After the decanter, the oil is also passed through a vertical centrifuge, which removes the remaining water and fine particles. If the paste was not heated above 27 °C in the process, the label may say "cold extraction".