1. Packaging and labeling. First look at whether the outer packaging is neat and clean, whether the handwriting is clearly printed, and whether the label is complete and formal. The labels of canned food produced by regular manufacturers are complete and clear, and should be marked with product name, factory name, address, ingredient list, net content, solid content, implementation standard code, quality grade and shelf life. Look at the product label and pay attention to distinguish the certification marks. Especially look at the production date and shelf life of food, and pay attention to whether the food exceeds the shelf life. If the trademark printing is rough, the printing of the factory place, factory name, production date and product name is incomplete; The solder at the welding part of the tin can is incomplete and uneven, and there is iron tongue and glue flowing at the curling part; The iron cover of the glass bottle is rusted, which may be inferior.

2. ingredient list, whether it contains preservatives. There are many kinds of preservative additives to prevent food from spoilage, such as sorbic acid and benzoic acid, but according to the relevant regulations of the state, canned food cannot contain preservatives. However, some illegal enterprises use preservatives in violation of laws and regulations in order to cover up their improper management of sanitary environment during food processing, inhibit the proliferation of microorganisms in food, maliciously extend the shelf life of food. Generally speaking, the production of canned food is completed in a high-temperature sterilization and vacuum sealing environment. At high temperature, any microorganism can be killed, and there is no need to put preservatives at all. There will be no quality problems within the two-year shelf life. It is reported that the small black jar of Jingyu has no additives or preservatives, and the tinplate packaging material can better preserve the nutrition of fruits.

3. Whether the color and luster are natural. Edible pigments are allowed to be used in some canned foods, but the amount and scope of use must be controlled within the national standards. Some illegal enterprises use pigments beyond the standard, or use pigments beyond the scope, and even use pigments that are not allowed to be used in canned food according to national standards, such as amaranth, lemon yellow, carmine and so on.

4. If the color of canned food is unnatural and the color is too beautiful, the pigment may be used in excess. When choosing canned fruit, we should first look at the pulp color of canned fruit, such as the normal canned yellow peach fruit, which should be uneven in color, golden yellow, and a little cyan. The pulp of fake canned yellow peach is completely the same, and the color looks good. The soup of a normal canned yellow peach should be colorless, while the soup of a dyed can is yellow. Another example is canned strawberries. Look at the soup first. If the soup is very red, it may be dyed. If the soup is slightly pink, it is normal.

5. Can shape, whether there is deformation. The terms are called fat listening and missing listening. Tinplate can has clean appearance, complete sealing, slightly concave bottom cover, no rust, no expansion, no deformation and no cracks; The glass can body is clean and free from dirt and fragmentation, the top cover does not rust and swell, the joint between the bottle cap and the bottle mouth is tight, there is no rust spot, the gasket is not skewed, and the glass bottle has a whole block, clear juice and no bubbles. When the can is polluted by microorganisms, the phenomenon of "fat listening" will appear, which is manifested by the bulge of the iron sheet center of the bottom and lid of the can. The reason is that the bacteria in the can multiply and produce gas, and the pressure in the can is greater than the air pressure. There are traces of mechanical extrusion and collision of the whole can, such as rust, fat, missing and shrinking, and dirt, darkness, spots and rust on the outside of the can.

6. Listen to the sound. Tap the center of the bottom cover of the can with your finger, and the sound is crisp and firm, indicating that the can is qualified and safe. Tap the bottom cover with your finger, the sound is cloudy and empty, indicating that there is more gas, and the can may have deteriorated. It is recommended not to eat it.

7. Check the air tightness. Put the can in water and press it by hand without bubbles, which shows that the air tightness is good. If there are bubbles in the bottom and cover of the water, it means that the air tightness is poor and it cannot be eaten.