The production process of rapeseed oil is divided into extraction method and pressing method. The pressing method is divided into “hot pressing” and “cold pressing”.
Leaching method: an oil-making process in which oil raw materials are soaked and extracted at high temperature to extract the oil. The production process is characterized by more heavy metal residues and high-temperature extraction of nutrient loss.
Hot pressing method: It is a traditional rapeseed oil production process after the rapeseed is fried or steamed at high temperature, and then physically pressed. The production process is characterized by high oil yield, less nutrient retention, low price, brown-red color, slightly astringent taste, and cannot be drunk directly.
Cold pressing method: refers to the vegetable oil extracted by physical and mechanical pressure under low temperature conditions, so it is called cold pressing method. Because there is no traditional high-temperature frying or steaming process, the oil is still distributed in the undeformed protein cells, and contains very rich ingredients inherent in rapeseed. (The characteristics of this production process are low oil yield, comprehensive nutrient retention, golden color, fragrance of rapeseed, non-greasy and non-hanging throat, and can be drunk directly.
Process characteristics of rapeseed hot pressing method:
1. It can increase the oil yield, improve the taste of the oil, and have a strong fragrance.
2. It is easy to cause high-temperature oxidative polymerization and decomposition to produce peroxides and certain harmful substances, destroying the nutritional content of species.
3. High temperature causes protein denaturation, greatly reduces the content of polyunsaturated fatty acids in rapeseed oil, and even produces trans fatty acids.
4. There are many impurities, such as rapeseed dander, phospholipids, free fatty acids, etc., which affect the appearance and color of the oil and the internal quality of the oil.
Advantages: The rapeseed oil is fried by the hot pressing process, and the rapeseed oil has a rich and mellow taste and a high oil yield.
Disadvantages: Roasting seeds at high temperature will reduce the content of active ingredients in oil and cause protein denaturation.