This problem involves a wide range of aspects. It is related to the types of raw materials of food and beverages, the corrosion factors in the soup, the manufacturing process of the solid cans, and the sealing and corrosion resistance of the empty cans. It involves almost all the main aspects of empty and solid cans.
When food cans contain acidic and highly acidic canned foods, the inner wall of the container often presents a uniform tin dissolution phenomenon. The surface shows fish scale corrosion spots, which are actually composed of small feather-like tin crystals. During this period, the residual oxygen in the can has been used up as an oxidant when the contents are oxidized and the can wall is corroded. If the material of the food can is tinplate, the steel base of the tinplate becomes the cathode and the tin becomes the anode. The tin dissolves into tin ions, and the steel base with micropores is not dissolved. The steel base is protected by the tin. The corrosion continues to develop, the tin layer dissolves rapidly, and the steel base has developed to a considerable area. At this time, tin and iron have begun to corrode together, and a lot of hydrogen is generated in the can. The hydrogen continues to expand and become a hydrogen expansion can. Some cans show perforation. To avoid the occurrence of can expansion, there are several specific countermeasures.
Common factors that cause low vacuum and can expansion can be divided into three categories: physical, chemical and bacterial:
I. Insufficient exhaust
Insufficient vacuum when sealing the can Or insufficient steam exhaust
The temperature of the soup added before sealing is too low
Improper configuration of steam jet exhaust device
The ribs and other contents are not pre-cooked thoroughly, and the air in the bones is not completely removed
II. Poor sealing performance or curling damage
The three-rate of the curling does not meet the requirements, especially the three-rate at the right angle of the special-shaped can is low
The reverse side hits the curling edge before sealing and is injured or hit, and the sealing structure is damaged
III. The external temperature is too high
The water vapor partial pressure in the can increases, causing the vacuum to decrease
Corrosion of the iron surface: The rapid dissolution of the tin layer on the inner wall produces a small amount of hydrogen and helium, which reduces the vacuum.
Corrosion on the inner surface of the paint tank: When the corrosion of the tank wall through the paint is serious, iron dissolution and hydrogen production corrosion will occur, resulting in a decrease in vacuum and subsequent hydrogen expansion.
Bacterial growth: Insufficient sterilization or secondary contamination after sterilization causes bacteria to grow in the tank, producing a large amount of carbon dioxide and other gases, resulting in tank expansion
Flat acid bacteria contamination:Poor sanitary conditions for storing low-acid raw materials in tanks, contamination with a large number of flat acid bacteria or insufficient sterilization intensity, resulting in flat acid bacteria growth, causing the product to become sour and the vacuum to decrease
As for preventive measures, I think if the cause is found, prevention will have a direction, and it will not be difficult for people in the industry to find solutions. If we want to discuss them one by one, the length may be too long, like a comprehensive textbook, which is boring to read. I think there are some examples of accidents at the end, so that we can discuss the matter, conduct some analysis and discussion, and find out the cause and preventive measures through analysis and research, which can be lively and solve practical problems.
