The crude oil that is squeeze out without filtering and refining is call crude oil after the initial pressing of the oil crop by the screw press. After crude oil is filtered and refined, the oil produced is called refined oil. The two are very different. Benteng machine will explain this in more detail.
Crude oil refers to animal and vegetable fats that have not been refined or leached. Its main component is a mixture of three fatty acids (commonly known as neutral oil); it also contains non-materials, collectively referred to as impurities. According to the dispersion state of impurities in the oil, it can be roughly divided into four categories.
1. Suspended impurities: including solid impurities such as sediments, preforms, powders, etc. The presence of these impurities is conducive to the activities of microorganisms, making the oil easily hydrolyzed and deteriorated and cannot be eaten;
2. Digestion impurities: including fat, protein, carbohydrates, etc., of which fat is the main one. The presence of these impurities not only causes the oil to be hydrolyze and deteriorate, and the appearance is turbid, but also produces a lot of foam and black sediment during the cooking process; the color and flavor of stir-fried vegetables and fried foods also lose the nutritional value of the fat itself, and have a certain degree of toxicity.
3. Oil-soluble impurities: including free fatty acids, pigments, hydrocarbon waxes, aldehydes, ketones, etc., as well as trace metals and environmental pollution, mercury, polycyclic aromatic hydrocarbons, aflatoxins, etc. The presence of these impurities is very harmful to the human body, and some impurities can also cause cancer to the human body.
4. Moisture: Crude oil contains a lot of moisture, and the presence of moisture can easily hydrolyze and deteriorate crude oil. Refine oil refers to refined oil that has been refine to remove harmful impurities such as edible and storage in crude oil and meet national quality standards.
There are three ways to refine crude oil:
1. Mechanical method: including precipitation, filtration, centrifugal separation, etc., mainly used to separate some digestible impurities suspended in oil from mechanical impurities;
2. Chemical method: there are mainly acid method refining and alkali method refining, in addition to oxidation method, etc. Acid refining uses acid treatment to remove pigments and digestive impurities, and alkali refining uses alkali treatment to remove free fatty acids. Oxidation is mainly use for decolorization.
3. Physical and chemical methods: mainly include hydration, decolorization, steam distillation and so on. Hydration mainly removes fat, decolorization mainly removes pigment, and steam distillation removes peculiar smell and free fatty acids. After the crude oil is refine, its moisture, impurities, acid value, and peroxide value meet the national quality standards, and it is not easy to rancidity and deterioration, which is conducive to storage. During the cooking process, it does not produce a lot of oily smoke and keeps the oily taste.
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