The shelf life of food refers to the period during which food can maintain safety and quality under specified storage conditions. The freshness, nutrients and safety of food after the shelf life will be affected. Secondly, salty kumquat is a kind of pickled food, the main ingredients are salt and kumquat, among which kumquat is rich in nutrition, but it can't completely kill microorganisms and bacteria in the pickling process, and it is easy to deteriorate. Twenty years is too long, which will lead to the deterioration of salty kumquat and breed a lot of bacteria and harmful substances. Eating such salty kumquat can not only provide nutrition, but also endanger health, with symptoms such as diarrhea and vomiting. Therefore, for the sake of safety and health, it is recommended not to eat expired salty kumquat.