Oil-containing snacks, peanuts, walnuts, sausages, tripe, etc. are easy to have a haram flavor. And lard and vegetable oil will change flavor after a long time. This is caused by the rancidity of edible fats and oils. Fats and oils rancidity is due to: ① due to the raw material residues of fats and oils and microorganisms produced by the enzymes caused by the enzymatic digestion of oil. ② Oil and grease are decomposed under the action of sunlight, high temperature, moisture and trace elements. The decomposition of fats and oils generates an unsaturated fatty acid, linoleic acid. Linoleic acid is very easy to chemical reaction with the oxygen in the air, producing a toxic substance with a strange odor. Such as aldehydes, ketones and certain peroxides. This phenomenon is called oxidation of fats and oils, also known as rancidity of fats and oils. Such rancid fats and oils emit a harry odor. Eating food with a haram flavor, easy to make people nausea, vomiting, and even abdominal pain, diarrhea. Vitamin E, vitamin, vitamin D, etc. contained in fats and oils are oxidized, thus the nutritional value of fats and oils is also significantly reduced. In order to prevent the food halla, in the process of food production should be removed from the oil residue, to avoid microbial contamination in order to eliminate and delay the enzymatic process, or add antioxidants. Commonly used natural antioxidants are peppercorns, cloves, vanillin, etc. When refining lard, put a few peppercorns, which can delay the time of lard halla. In addition, greasy food packaging should be tight, as far as possible so that the food does not come into contact with the air. Grease food should be placed in a cool place, preferably stored in brown bottles, can also prevent the oxidation of oil. Extended reading do not drink raw soybean milk or uncooked soybean milk is not cooked cooked eel can not be eaten to reveal the hidden truth of food additives