Pi Dan, also known as century egg, is made by using alkali to denature and coagulate the protein of fresh eggs, and partially decomposing the protein to form a translucent body ranging from light to dark black, which has a unique flavor. As waterfowl are more susceptible to carrying Salmonella and other microorganisms, any finished Pi Dan that is damaged is inevitably heavily contaminated and therefore should not be eaten. During the processing of Pi Dan, some places add a small amount of litharge (lead oxide) to the auxiliary materials. Excessive lead can damage the human nervous system, hematopoietic organs, and kidneys. To prevent the harm of lead to the human body, our country has stipulated that the lead content in Pi Dan must not exceed 3 mg/kg. In addition, during the storage of Pi Dan, as water evaporates, the texture not only becomes harder but is also difficult to digest. Therefore, Pi Dan should not be stored for a long time, and the storage period is about one month.