Bleaching is usually performed in several stages. Prior to bleaching, the
oil is properly de-aerated (to avoid oil oxidation and deterioration) and dried (to avoid hydrolysis) under reduced pressure (< 100 mbar) down to a moisture content of 0.1%. De-aerated bleaching earth is added to the oil and the whole is further heated under reduced pressure (~30 mbar) and high temperature (80–120°C) and intensively mixed (sometimes by injection of steam) to ensure intimate contact.