1.Look at the shape of the can to see if it is deformed. It is called fat listening or missing listening. The tin cans must be kept clean on the outside, with complete sealing. The bottom cover of the tin cans should be slightly concave, free from rust, expansion, deformation and cracks; The body of the glass can shall be clean and free of dirt and fragmentation. The top cover shall not rust or expand. The joint between the cap and the mouth shall be tight and free of rust. The gasket shall not be skewed. The objects in the glass bottle shall be intact, the juice body shall be clear, and there shall be no bubbles.
3. Check the air tightness. Place the can in clean water, and press it with hands without bubbles. The processing of the can shows that the food in the iron can has good air tightness. If there are bubbles on the bottom and cover when placed in water, it indicates that the air tightness is poor and the food inside is no longer edible.