Crushing oil by earth has a weak advantage but not a small risk.

In many parts of China, there are also local press workshops, and many people buy small oil press to squeeze their own oil. Many people believe that such "untreated" and "non-added" oils are healthier and safer.

However, the reality is cruel: not only is it not safer to squeeze oil, but there are many risks.

The crude oil contains free fatty acids, pigments and volatile components. The presence of these impurities makes the oil have its own unique flavor. But they also make oil smoke at lower temperatures. The temperature at which oil begins to smoke is called the "smoke point". Smoke point is related to the type of oil, such as sunflower seed oil smoke point is less than 110 C, while sesame oil is close to 180 C. The smoke point of the same kind of oil is closely related to the impurities. The smoke point of soybean and peanut crude oil is about 160 C, and after refining, it can reach over 230 C.

Fume is not only the source of PM2.5, but also contains a substance called acrolein. Acrylic aldehyde has a strong stimulating effect on the eyes and respiratory tract, and was even used as a chemical weapon in World War I. In addition, smoking can produce other harmful substances. Commercial oils are usually refined to remove free fatty acids, pigments and odors. The refined oil is light in color, light in taste and bright in appearance. The smoking temperature can be increased by 50 or 60 degrees Celsius. When fried, refined oil will not smoke at higher temperatures.

Usually, the crude oil will be treated at high temperature, and some benzopyrene will be formed in the process of treatment, which is a carcinogen. In the past few years, media reported that benzopyrene in a tea seed oil exceeded the standard. The reason for exceeding the standard is the high temperature heating before pressing.

In addition, vegetable oil is easy to oxidize because of its high content of unsaturated fat. This oxidative deterioration occurs continuously and has already exceeded the national standard before it can be identified by the naked eye or changes in flavor. That is to say, although it is "squeezed by oneself", no one will investigate whether it is unqualified, but if it is tested, it is likely that it is already unqualified "deteriorating oil". Commercial refined oil not only removes impurities and slows down oxidation, but also adds appropriate antioxidants to further increase its shelf life. So refined oil can be preserved longer than self-extracting oil.

The greater risk of crushing oil is aflatoxin. Whether it is peanut, soybean or rapeseed, it is possible to be infected by aflatoxin. In the process of oil refining, most aflatoxins will be removed, so it is not easy for refined oil to exceed the aflatoxins standard. Without refining the self-extracting oil, the possibility of exceeding the standard is very high. In fact, in the past few years, there have been frequent reports of aflatoxin exceeding the standard of "earth-pressed oil", the extent of exceeding the standard is as high as several times. The doubling of aflatoxin M1 in milk has alarmed many people, while aflatoxin B1 in oil is 10 times more toxic, and the extent of exceeding the standard is often greater. In fact, the national standard limit is 20 to 40 times that of milk standard, so even considering that the consumption of oil is smaller than that of milk, the risk of exceeding the standard is still much higher.

Many people worry about trans fats in oil refining. In theory, high temperatures and prolonged treatment do convert some unsaturated fats into trans fats. However, in a reasonable refining process, the conversion rate is not high. According to the survey data of the National Center for Food Safety Risk Assessment and Exchange, in recent years, the content of trans fats in vegetable oils on the Chinese market is about 1%. Considering the amount of vegetable oil consumed by everyone every day, the health risks associated with trans fats are negligible.

Considering the "unhealthy" factors of self-extracting oil and refined oil, from a safety point of view, "self-extracting oil" is not as good as refined oil.