After impurities are removed from oil with the methods of degumming , neutralization , dewaxing and bleaching ; some oils contain certain compounds wich may not only tarnish oil and reduce the charm in appearance but also tend to sink under low temoerature . These compounds develop waxes ( fat alcoholes in succession ) , stearins and saturated glycerides which have high melting point in oils particularly such as those of sunflower , corn cottonseed , olive and rice according as the type of oil . The crystals formed in the oil refrigerated gradually and kept in attendance of a slow mixture under low temperature as well , are removed via filtration .This process is called winterization .Winterized soil ,that is to say ,perlit is used to start the crystallization in winterization process and improve filtration and those perlits are distilled via filtraton.