c) Bleaching

Heating the oil to 85ºC and treating it with adsorbents which are termed bleaching earths (Fuller’s earth, acid activated montmorillonite clays or activated carbon) permits an almost complete elimination of all colouring materials.

Attention should be paid to prevent oxidation during bleaching. Phospholipids, soaps and some oxidation materials are also adsorbed alongside the pigments. Filtration is then performed to remove the spent adsorbent.

Research into other types of adsorbent, including silica-based ones and composite materials, may one day result in oils which did not need deodorization, and also in materials which can be (relatively) cheaply reused or recycled.