Why some cooking oil "lampblack" larger?
The main component of oil is triglyceride, and there are a small amount of free fatty acids, glycerides, unsaponifiables and other substances with low molecular weight. These substances are easier to volatilize than triglycerides, so "lampblack" appears when cooking at high temperature.
Free fatty acids and other volatile substances in oil can be removed by refining. The temperature of cooking fume is "smoke point", and the level of "smoke point" can be used as an indicator of the refining degree of vegetable oil. The refined cooking fume point is about 210 ℃, and there is basically no "smoke" when cooking. The unrefined cooking fume point is lower, and the "smoke" is larger when cooking.
How is the color of oil blackened and darker?
The color of crude oil made by pressing or other methods is dark, which affects the sensory and cooking quality. The main purpose of decolorization is to remove the pigment from the oil. But at the same time, decolorization can also remove trace heavy metals, residual soap, phospholipids, pesticides, polycyclic aromatic hydrocarbons and other harmful substances to human body, so decolorization is very necessary.
At present, the commonly used decolorization method is adsorption decolorization, that is, using adsorbent to adsorb pigment and other impurities in oil.
At present, the commonly used adsorbents for oil decolorization are activated clay and activated carbon.
Activated clay is a kind of natural bentonite (mainly montmorillonite), which is processed, odorless, tasteless and non-toxic.
Activated carbon is made by carbonization of branches and shells, and then activation treatment, which is non-toxic.
After the adsorbent adsorbs the pigment and other impurities in the oil, it needs to be separated from the oil by filtration.
What is crude oil? Why should crude oil be refined to be edible?
Animal and vegetable oils obtained by pressing, leaching and water substitution are collectively referred to as crude oils.
Some components in crude oil not only affect the safe storage of oil, but also reduce the quality and use value of oil and endanger human health
The existence of impurities and water will be conducive to microbial activities and promote the deterioration of oil.
The presence of phospholipids not only causes the hydrolysis and rancidity of oil, but also produces a large amount of foam in cooking and produces black precipitation, which affects the color and flavor of food.
The content of free fatty acid marks the degree of rancidity of oil. The high content of free fatty acid will lead to a large amount of "lampblack" in cooking.
The pigment not only makes the oil dark and affects the appearance, but also individual pigments such as gossypol are toxic.
Wax affects the transparency of oils and fats. When cooking, it will smoke and produce a choking smell.
Trace amounts of heavy metals can promote the oxidation and rancidity of oil, and also produce residues in human body.
Aflatoxins, polycyclic aromatic hydrocarbons and pesticide residues are harmful to human body, and some of them can cause cancer.
Therefore, in order to ensure human health and prolong the storage period of edible oil, crude oil must be refined to remove harmful substances.
Refining oil equipment is mainly used to process crude oil to make raw materials meet the standard of barreled oil (which can be bought in the supermarket) or national high-grade edible oil standard. Crude vegetable oil is only the product of oil extraction, it contains harmful substances to consumers. Some of these substances exist naturally, and some are produced in the process of production or storage. For people's consumption, these substances must be carefully removed. Because of their different origins, refining must be carried out in several steps under different conditions. With the difference of crude oil, the refining process is divided into degumming, deacidification, decolorization, deodorization, degumming and so on. According to the variety of crude oil, some or all of them can be used.
The edible oil standard adopts a new way to divide the edible oil into grade one, grade two, grade three and grade four (grade four is the lowest grade), which are respectively equivalent to the original salad oil, high-grade cooking oil, grade one oil and grade two oil.
