Our traditional preserved eggs use lead oxide to provide metal ions. Therefore, in the process of lead ions decomposing long-lasting sulfide ions with the protein in the egg to generate insoluble salt sulfide, which blocks the pores of the eggshell, the lead Ions also seep into preserved eggs.

Many studies have confirmed that lead has a huge toxic effect on the human body, mainly damaging the nervous system and affecting children's memory, language, motor ability and learning ability. Therefore, more and more lead-free processes are used to make preserved eggs. The lead-free process means that lead compounds are not used to provide metal ions during the processing of preserved eggs, but zinc, iron, copper ions or a combination of these ions are used to provide metal ions.

However, it should be noted that lead-free preserved eggs does not mean that preserved eggs are completely lead-free, because in the nature we live in, the air, soil, and water will contain trace amounts of lead. These lead will be present in the ingredients we cannot make preserved eggs. The missing raw material is fresh eggs. Therefore, it is almost impossible to make preserved eggs absolutely lead-free.