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Depending on the type of the raw material (seed, fruit or germ) the process of edible oil production can vary. In case of medium or larger-sized seeds (e.g. sunflower) to obtain oil the seed is dehulled and the oil is pressed from the kernel. The oil remaining in the presscake is removed by extraction. The oil obtained by pressing and extraction - called crude oil - has a dark colour, a characteristic smell and is turbid. This oil can be used to make salad dressings but is not recommended for frying. The aim of crude oil refining is to achieve better oil quality with a wide range of applications and longer shelf-life. The crude oil is refined in the course of gentle processes. During refining all the undesirable compounds, which have a negative influence on the oil's appearance like sediment formation during storage, pigments or odour compounds are removed. On the other hand, valuable compounds such as vitamins and sterols are retained. Phosphatides, which cause turbidity in the crude oil are removed during degumming, while the colour materials and metal traces are adsorbed and filtered during bleaching. Sunflower oil also contains waxes, which can crystallise at low temperature and make the oil cloudy. To remove waxes the oil is cooled down and formed crystals are filtered. In the last step of refining the oil is stripped by steam to remove the odour materials and the free fatty acids, which deteriorate the organoleptic parameters and the shelflife of the refined oil. The fully refined oil produced by the above process is light-coloured and clear with a neutral taste and smell. Refined vegetable oil can be used to make dressings, mayonnaise, for frying and cooking.
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