What are the extraction methods of edible oil?

There are two technological methods for extracting edible oil from plants, chemical extraction and physical extraction, namely, leaching method (chemical method) and pressing method (physical method). Pressing method: The pressing method has a long history and its technological process is relatively simple: after the oil is steamed and fried, the oil is squeezed out from the oil by mechanical method. The ancient squeezing method required the operator to pay heavy physical labor. However, the content of residual oil in the extruded oil residue (oil cake) is quite high, which wastes extremely valuable oil resources. Modern pressing method has realized industrialization and automatic operation, but the problem of high residual oil content in oil residue still cannot be solved. From the pretreatment of pressed raw materials, there are cold pressing method and hot pressing method, also called cooked pressing method. Cold pressing is to put raw materials directly into an oil press to extract oil without baking or cooking. This method is light in color and bright in color, but the oil yield is low and the oil taste is not strong or alcohol. Cooking and pressing need to dry oil crops before pressing, so as to reduce the moisture content of raw materials and increase the activity and fluidity of oil molecules, thus improving the oil yield and ensuring the delicate taste of oil. But it also destroys the chemical composition of the oil, which leads to the darker and darker color of the oil.