Canned food, also known as preserved food, refers to processed food where the raw materials are pre-treated and then sealed in containers or packaging bags. Through sterilization processes, most microorganisms are killed, and under conditions of a sealed and vacuum environment, it can be stored at room temperature for a long time. 

Most canned foods do not contain preservatives. Only a small number of canned foods may add a small amount of preservatives due to process or raw material limitations. 

The long shelf life of canned food is mainly determined by its production process. Generally, the production of canned food involves raw material pre-treatment → canning → exhaust and sealing → sterilization, cooling → temperature preservation inspection → packaging. 

After this series of operations, the inside of the can is an oxygen-free and sterile environment, which naturally allows it to last for a long time.