The so-called canned food refers to the food that can be stored at room temperature for a long time after being packaged in a sealed container and subjected to moderate thermal sterilization (commercial sterility). Canned food is a kind of traditional food with various packaging forms and varieties, which is convenient to eat and carry. It is very convenient and important for the dietary supplement of floating people such as travel, field work, national defense, mining and exploration. But if you don't choose it properly, it will endanger your health. This paper introduces several common metamorphic cans to help distinguish them.

(1) Corrosion of corrosion tank can be divided into external corrosion and internal corrosion. There are many reasons for corrosion, such as incomplete penetration, cracks, corners, depressions and perforations. , resulting in juice overflow, dirty tank, rusty spot; Iron is exposed in the packaging skin, or the solder falls off, resulting in rust spots or iron sulfide spots in the tank. Small pieces of solder or glue will flow in the tank, and the content of heavy metals is often high. No matter whether it is external rust or internal rust, once the tank wall is perforated, its contents will be contaminated by bacteria, and the heavy metal content in the food in the tank exceeds the standard and cannot be purchased.

(2) Fat listening is drum listening. When the pressure in the tank is greater than the air pressure, the two bottom ends of the tank expand and protrude, which is called fat listening. Fat listening can be divided into biological fat listening, chemical fat listening and physical fat listening.

Bio-lipo-aurantium is produced by incomplete sterilization or bacteria re-entering canned food to decompose food, producing carbonic acid gas and lipo-aurantium. This kind of fat listening is called corrupt fat listening, and it is also called really fat listening. After opening the bio-fat tank, there are often unpleasant acidic and corrosive gases, which are harmful to human body and cannot be eaten.

Chemical fatness is due to the acidity of the food in the canned food, uneven tin layer on the inner layer of tinplate, or damaged tin layer. Organic acids in food react with iron for a long time, causing chemical reaction, releasing hydrogen to gather in the tank, and the pressure is too high to form fatness. This kind of fat listening mostly occurs in canned fruits with high acidity. After listening to fat, the content is easy to change color and the content of heavy metals is also high, so it is not suitable for purchase.

Obesity is mainly caused by excessive contents, insufficient exhaust, frozen canned food or improper operation. Physical fat cans are generally called fake fat cans, and the food in cans has not gone bad and can be eaten.

(3) The food in the tank is discolored, turbid and precipitated. This phenomenon mainly exists in glass cans for many reasons. For example, canned glass is discolored by direct sunlight during operation; Some storage temperatures are too high, which promotes the decomposition of fat and the transformation of sugar in the tank, thus making the juice in food turbid and dark. Some of them are caused by vibration during transportation and loading and unloading, and the contents are shattered and so on. Canned food with this phenomenon can't be bought and eaten.

(4) rot and deterioration. After this kind of canned food goes bad, it does not produce fat hearing phenomenon and its appearance is normal. It is mainly caused by the decomposition of contents by anaerobic bacteria such as Botox. This kind of canned food can smell rancid and sour when the lid is opened, and it is absolutely inedible. Because of the poisoning caused by Botox, not only the symptoms are serious, but also the mortality rate is high, so we must not be careless.

In view of the above situation, we must not take it lightly when choosing canned food.

1. First of all, we should see that the commodity marks and trademarks should be complete and clean, which can explain the food in the can. Such as main raw materials, net content, eating method, storage conditions, product standard number, etc. ; Factory code, factory name code, production date, product code, etc. are hard printed on the can cover. If the trademark information is incomplete and shoddy, it is an unqualified product. When choosing the production date, it is best to choose the nearest product.

2. Observe the jar. For tinplate cans, the surface is clean without rust, the bottom and lid are slightly concave, the seams and bottom edges are not damaged, there is no iron tongue, and the cans are tightly sealed. It's usually a good can. For glass cans, we should first observe whether the contents are turbid, precipitated and discolored. A good can should have a normal color (the true color of food), a complete block, a clear soup color, no sediment at the bottom of the can, a slightly concave lid, and no rust on the iron lid and rubber band.

3. Listen to the sound and tap the center of the bottom cover with your finger. The sound is crisp and firm, indicating that it is a good can; The voice is turbid and empty, indicating that the content is insufficient and there is much gas; The hoarse voice of "broken, broken" indicates that the can has gone bad.

4. Pay attention to whether the color, taste and shape of the food in the can are normal when opening the can. If it is found to be moldy, smelly, lumpy and porridge-like, it means that the food has deteriorated and is not suitable for eating.