Toll-refining

The first step of refining is known as degumming. Its purpose is to remove seed particles, impurities, and most of the phosphatides, carbohydrates, proteins and traces of metals.

The crude oil is treated with food grade processing aids and/or water at a temperature between 55-70°C, which leads to hydration of most of the phosphatides, proteins, carbohydrates and traces of metals. The hydrated material separates from the oil and is removed.

Neutralization reduces the content of the following components: free fatty acids, oxidation products of free fatty acids, residual proteins, phosphatides, carbohydrates, traces of metals and a part of the pigments.

The oil is treated with an alkali solution (caustic soda) that reacts with the free fatty acids that are present, converting them into soap stock. The mixture enables the separation of the oil phase which floats on top and is free from fatty acid, from the layer phase of soap, alkali solution and other impurities which are then drawn off.

Water is used to wash out any soap residues that remain in the oil. With the addition of water, which is heavier than oil, it sinks along with the remnants of soap which bind to the water and can then be drained from the pre-treatment boiler.

The underlayer, which is made up of soap and other impurities, is drawn from the oil and is a solid material when mixed with water. 

The purpose of bleaching (or decolorizing) is to reduce the levels of pigments such as carotenoids and chlorophyll but it also serves to further remove residues of phosphatides, soaps, traces of metals, oxidation products, and proteins.. These trace components would otherwise interfere with further processing.

If vegetable oils contain unacceptable levels of PAH's (polycyclic aromatic hydrocarbons), carbon is added to absorb and eliminate the PAH's. The used activated carbon is separated by filtration and disposed of in a suitable manner, outside of the food and feed sector.

All physical impurities are removed from the oil via filter plates, including earth and/or active carbon, following bleaching. The used bleaching earth and activated carbon are disposed of in a suitable manner outside of the food and feed sector.

Deodorization is a vacuum steam distillation process that removes the relatively volatile components that give rise to undesirable flavors, colors and odors in fats and oils. This is achievable due to the significant differences in volatility between the undesirable substances and triglycerides.

The purpose of deodorization is to reduce the level of free fatty acids and to remove odors, off-flavors and other volatile components such as pesticides and light polycyclic aromatic hydrocarbons by a stripping media. Precise execution of this process will also improve the stability and the color of the oil, whilst preserving the nutritional value.

Depending on the residence time in the deodorizer, the process is carried out under vacuum at temperatures ranging from 180-250°C. As the substances responsible for odors and flavors are usually volatile, stripping steam is also applied. Conditions are modified within this range as required to ensure the successful removal of specific substances.

After deodorization, the refined product must be cooled. The optimal temperature for fats is between 60 - 80°C and for oils 20 - 25°C. The cooling process must take place under vacuum as without it would result in the burning of the refined product at the steamer temperature, which would then be deemed unsuitable for the customer.

Winterization is a process whereby waxes are crystallized and removed during filtering to avoid clouding of the liquid fraction at cooler temperatures. The oil is cooled to 8-14°C. A filter aid is added during cooling. The filter cake that remains after the filtering process consists of oil, waxes and filter aid.