WHAT IS OIL REFINERY AND REFINED COOKING OIL ?


We know that the cooking oil is the primary requirement of the people and hence the production of cooking oils and fats is among the world's oldest industries. Before one century the same oils were obtained by animal operated simple machineries. In this system there was not any purification facility of the oil. Then the expeller crushing system with filtration facility has developed which is still used at everywhere. It is called the mechanical extraction system through big oil mills or small oil mills. Still people are using such filtered cooking oils since very long time at everywhere. But as per the scientist views, (free fatty acids - ffa) and colors of filtered cooking oils are some times harmful to the human health. Moreover some taste and flavors are also undesirable. Hence to remove the ffa, colors, smell and taste from the cooking oils like cottonseed oil, soybean oil, palm fruit oil, palm nut oil, coconut oil, maize (corn) oil, mustards oil, peanut (groundnut oil, sunflower oil, sesame oil etc. are refined in the refinery plant. Hence at present there is a big craze for refined oils only. Thus the refined oil will be free from free fatty acids, colorless, odorless and tasteless.

HOW OIL IS REFINED :

As mentioned above to remove the ffa, color and smell - odor, any cooking oil can be refined. It can be divided in to mainly three different processes.

- Neutralizing (Defatting)
- Bleaching (Decolouring)
- Deodoring

Other processes appear before, after or somewhere between these three operations, whenever this applies, we will mention it in the relevant part.

NEUTRALIZING :

This is the first process of refinery. It is also called the alkali neutralizing process. In every cooking oil there will be some proportion of free fatty acids - ffa that increase the rancidity in the oil and it is harmful to the health. The ffa percentage is found different in different oils at different stage. In some fresh oils of fresh oilseeds like groundnut oil, sesame oil, sunflower oil the ffa percentage will found very less. Hence it can be also used directly without refined for eating purpose. While cottonseed oil, palm oil, soybean oil, corn oil, coconut oil is having a high ffa hence it is advisable to use these oils after refining. But in some countries these oils are also used without refining as per people's choice. The refined oil can be stored for long time.

Any crude oil will be heated in the neutralizer with continues and required type of stirring at required temperature by adding the required quantity of caustic soda (sodium hydroxide - NAOH). During the process, ffa will be separated in form of soap stock, which can be used in the preparation of laundry soap. To remove the alkali particles, the water wash to the neutralized oil is given. This operation is done in the same vessel of neutralizer.

Degumming :

Some times some particles or impurities are found in dissolved form in the oil and which increase the turbidity of oils. Such impurities cannot be separated by neutralization or filtration. Degumming is the treatment of crude oils with water, salt solution or dilutes acids such as phosphoric, citric or maleic to remove phosphates, waxes and other impurities. This process require in very rare cases. Most of the cooking oils in U.S.A. also are refined without degumming. Even though this operation is also done in the same vessel of neutralizer.