The oil finally produced from the oil processing plant is of god quality with light color. Also, we take care that free fatty a-cids present in oil can be also filtered out for edible grade or for animal feed application. In addition to this, for animal oil, an addition process of dewaxing is also carried out for separating our wax.
 
Basically animal oil has following impurities which needs to be removed.
 
1) PHYSICAL IMPURITIES:

Left over particles of oil seeds etc. By simple filteration process these impurities are removed.
 
2) PHOSPHATIDES, GUMS AND WAXES:

During pretreatment process gums and other impurities are either separated out, either through batch degumming or through continuous process with help of centrifugal separators.

When impurities are only in small quantities Gum conditioning process is adopted, where in gums are just precipitated and are removed in next neutralising process.
 
3) FREE FATTY A-CIDS:

Popularly known as F.F.A. all animal oils are compound formed by Glycerin and Fatty A-cids when Fatty A-cid separates out from the bond with Glycerin they are termed as Free Fatty A-cids. The free Fatty A-cids are generally removed by neutralising them with alkalies like caustic soda.

The soap stock formed and the oil are then separated out by decantation process in Batch Neutralising or by centrifuge separation in continuous Neutralising.
 
4) COLOURING PIGMENTS:

Depending on the quantity and type of colour pigments present in the oil, oils have colour ranging from light yellow, reddish to dark brownish (as in crude cotton seed oil). To give uniform, colour it is essential to bleach the oil with the help of bleaching agents like bleaching earth / activated carbon. Bleaching agents absorbs the colouring pigments.

By filteration process the spent bleaching agent is filtered out. Sometimes caustic treatment in neutralising section also reduces the colour of oil specifically in cotton seed oil.

In case of palm oil colour is also reduced by heat treatment. Bleaching operation is performed either as batch process in smaller capacities or as continuous operation in large capacity plants.
 
5) ODOUR:

Every oil has its own district odour sometimes pleasing odour sometimes unpleasant odour. Neutralising and bleaching process also adds odour to the oil which is unpleasant. It is therefore essential to remove the odour from oil. Deodorisation is the process to remove odiferous matter from animal oils.

The odour is removed by injecting open steam in the oil which is heated to high temperature and kept under high temperature and kept under high vacuum. The odiferous matter distills off at high temperature and high vacuum and is carried away through vacuum system. The oils is cooled.
 
6) WAXES:

Some animal oil have waxes present in them. At low temperature waxes appears and gives hazy appearance to oil. Consumer does not prefer such hazy appearance.
 
Dewaxing process is adopted for separation of waxes from oil. Oil is cooled and chilled in crystallisers the waxes are crystallized. The wax crystals are separated out either by cold neutralization in centrifuges or more common method of separation is filter them out in horizontal pressure leaf filters.

The oils which is thus treated for removal of gums, free fatty a-cids, colouring matter and odour is refined oil. In oils like palm oil, free fatty a-cids are removed during deodorisation it self without chemical caustic treatment and hence process is called physical refining.