Which Is Better, Hot Pressing Or Cold Pressing?
Hot pressing and cold pressing are both a process for pressing edible oil. Most of the vegetable oils we consume in our daily life are hot pressed oils, that is, before pressing the oil, the oil is first cleaned and crushed, and then heated at high temperature to make a series of changes inside the oil: destroying oil cells, causing protein denaturation, reducing oil viscosity, etc., so as to be suitable for pressing oil and improving oil yield.
1. Hot pressing process: rapeseed - cleaning ~ softening - rolling embryos ~ steaming and frying - pressing
Operation instructions: Rapeseed is screened with a 30 mesh/inch screen to make the rapeseed contain less than 0.5% impurities, and then softened. After softening, the rapeseed contains about 9% moisture, and then rolled embryos and steamed and fried. Steaming and frying make the oil temperature reach 110-120 degrees, and its moisture content is about 1-1.5%, then it can enter the oil press for pressing. If a cylindrical wok is used, the rapeseed can be directly put into the cylindrical wok after cleaning and removing impurities, or it can be put into the flat wok after rolling. However, 2-3% water is added when frying the seeds. When the seeds are fried to 110-120 degrees, they can be taken out of the wok for pressing. The following methods can be used to judge whether the rapeseed is fried well during hot pressing. Rub the rapeseed with two wooden boards. If the shell and kernel are separated and the kernel is dark yellow, it is suitable. If the kernel is powdery, it is too dry. If the shell and kernel are not separated, it is too wet.
Advantages of hot pressing process
Hot pressing is to fry and roast the seeds of oil crops and then squeeze them. It has a special fragrance, darker color and higher yield. There are fewer residues in the product and it is easy to preserve. Cold pressed seeds are not fried and roasted, so the smell is poor, but the color is good. There is no solvent residue in both pressing methods.
Hot pressing: hot steaming and frying, skin pressing oil production process. First, the raw materials must be stir-fried in a pan, and then the oil is pressed by an oil press. The advantages of this process are high oil yield and low residual oil.
Disadvantages of hot pressing process
However, the crude oil squeezed from the oil after high temperature treatment is darker in color and has a higher acid value, so the crude oil must be refined before it can be eaten. At the same time, high-temperature oil pressing causes a large loss of bioactive substances (vitamin E, sterols, carotenoids, etc.) in the oil during the pressing process, resulting in a waste of resources.
In recent years, with the continuous improvement of people's living standards, people are increasingly favoring cold-pressed oil in terms of edible oil. Cold-pressed oil is sent to the oil press for pressing without heating or low temperature before the oil is pressed. The squeezed oil has a lower temperature and a lower acid value, and generally does not need to be refined. After precipitation and filtration, the finished oil is obtained.
2. Cold pressing process:
Rapeseed can also be cold pressed. During cold pressing, the rapeseed is cleaned and impurities are removed. 1-2% water can be added to soften the rapeseed. After softening, it can be rolled into embryos. It can also be pressed into the oil press without rolling embryos (but pressing after rolling embryos can improve the performance of the oil press). The moisture content of rapeseed during cold pressing will directly affect the oil extraction efficiency, so it is very important to judge the dryness and wetness of the oil. Generally, the moisture content of rapeseed is controlled at 5-8% before pressing. The traditional method to judge the moisture content of rapeseed is to squeeze the rapeseed with your fingernails. If there is a sound and it is divided into two pieces, the moisture content is appropriate. If it is powdered, it has too little moisture and is too dry. If it is flat, it has too much moisture and is too wet. Problems that may occur during the oil press: The oil content in rapeseed has reached about 33-40%. Generally, there will be no abnormal phenomenon when hot pressing according to the instructions. If the cold pressing is due to improper operation or inappropriate moisture content of the oil, the temperature of the oil press body is not good, there will be slag leakage, oil return or feeding problems. At this time, you can refer to the cold pressing of peanut kernels for treatment.
1. Process flow: rapeseed → screening → adding warm water → mechanical stirring → heat preservation and moistening → making cakes → pressing → finished product
1) Screening: Screen out impurities such as fragments to ensure that there is no hardness when pinched by hand.
2) Add warm water: Add 50℃ warm water 3~4%.
3) Stirring: The stirrer rotates 480~500 times per minute. Stir for 10~15 minutes and the temperature rises to 54~58℃.
4) Heat preservation and moistening: There are two methods. One is to use steam heating pipes to keep the entire workshop warm; the other is to keep the press warm. That is, the press is sealed with wooden boards to prevent the cake temperature from escaping and maintain the required temperature. Practice has shown that the room temperature is maintained at about 30°C, and the oil press insulation method can increase the oil yield. Keep warm for 30 minutes, the temperature is 56-58°C, and the moisture is 13.5-13.8%.
5) Make cakes and press: Each cake weighs about 2 kg, and the moisture content is about 13.8%. If you want to see the on-site operation of the pressing process, you can go to Henan Dongying Machinery Equipment Co., Ltd., where technicians can test the oil press process for you on-site.
Advantages of cold pressing process
Cold pressing is a process for producing oil. Generally, cold pressing is carried out in an environment below 60°C, and the nutrients are retained intact. Since the oil yield of cold pressing is only half of that of hot pressing, the price of most cold pressed oils is about 50% higher than that of hot pressed oils. Because the cold pressed oil is not damaged, it generally does not need to be added with additives, so it can be stored for a long time. The market value is relatively high.
Cold-pressed oil has pure natural characteristics and avoids the adverse effects of traditional high-temperature oil pressing. Cold-pressed finished oil retains the natural flavor and color of the oil, and completely preserves the physiologically active substances in the oil (vitamin E has anti-aging function, sterols have skin-building effects and enhance human metabolism). Cold-pressed oil is original and is a choice for healthy life. However, most oils are not suitable for cold pressing. Taking soybeans, high-erucic acid rapeseed, cottonseed, peanuts, and sesame as examples, the beany smell contained in soybean oil, the spicy taste in high-erucic acid rapeseed oil, the gossypol toxin in cottonseed oil, and the aflatoxin in spoiled oil must be refined to remove. The fragrance of sesame oil and fragrant peanut oil must be obtained through hot pressing. The raw materials of cold-pressed oil must be carefully selected, otherwise the quality of cold-pressed oil will be seriously affected by the different maturity of the raw materials and the harmful substances contained in the raw materials (such as aflatoxin in moldy oil and gossypol toxin in cottonseed). Generally speaking, cold pressing has a low smoke point and unstable water content, which is not conducive to long-term storage.
Disadvantages of cold pressing process
Cold pressing generally requires crushing before the oil output can be increased, and sometimes it needs to be pressed twice or three times. Hot pressing is generally used for pre-pressing of large machines, that is, the first oil pressing, but some manufacturers have improved the model and directly used it for oil pressing without other equipment. For example, Dongying Machinery uses a three-stage pressing screw and three pressing bars. Basically, the material embryo can have a good oil yield in one pass. Cold pressing is a machine that can press oil without frying the oil in a wok. The color of cold pressed oil is good and relatively light, but the oil smell is not fragrant and does not get angry. The key is that cold pressed oil will not foam or stagnate when frying.
Which is better, hot pressing or cold pressing?
Hot pressing means that the oil is fried in a wok before pressing. The cooked oil has a pure and fragrant taste, especially sesame and peanuts, which are rich in oil. The disadvantage is that when it is not processed, it will foam and sludge the pot when it is fried, but this problem can be solved by simple treatment with a centrifugal oil filter.
Cold-pressed oil is generally used for the pressing of high-end market fine oils because of its small output and low production efficiency, such as linseed oil, walnut oil and other fine oils, which need not destroy the nutritional components of the oil. The cold-pressing process is suitable for mass-produced edible oils for civilian use. Although the oil quality is not as good as cold-pressed oil, this problem can be solved by filtering and removing impurities. Therefore, users should choose different processes according to their own consumer groups.
