To produce refined oil, crude palm oil and crude palm kernel oil are processed through three refining stages, namely degumming, bleaching and deodourising.
In degumming, the gum and fatty acid in crude palm oil and crude palm kernel oil are separated together with other impurities such as trace minerals, copper and iron by the application of phosphoric acid.
In bleaching, the oil is mixed with bleaching earth (bentonite calcium) in a vacuum room to remove impurities and colour pigments in the palm oil.
In deodourising, the odour and taste of the oil are removed when the oil is steamed at high temperatures of between 240°C to 260°C and then cooled to room temperature.
cr : http://www.wilmar-international.com/our-business/tropical-oils/manufacturing/refining-into-refined-bleached-and-deodorised-rbd-palm-oil-and-rbd-palm-kernel-oil/