The process of refining the olive oil can be a chemical or a physical process. In the chemical process, caustic soda is added to the oil to draw out the fatty acids. In the physical process, which is being used increasingly, olive oil is put in a drum, which is heated up in a vacuum, to about 180ºC. This evaporates the fatty acids and they are drawn off. In this way the oil is neutralised and deodorised.