Compared with ordinary duck eggs, some protein in salted duck eggs is decomposed into amino acids. As a result of salting, the salt in eggs increased, and the inorganic salt in eggs also increased slightly. Because the fat in raw egg yolk is combined with protein, you can't see that it contains fat. After a long period of ripening, protein will denature and separate from the fat. When the fat gathers together, it becomes egg butter, which contains red and yellow vitellin and carotene. When dissolved in egg butter, it is red and yellow, which increases the sensory characteristics of salted eggs. Oily salted duck eggs are a sign of good pickling. In addition, salted duck eggs are rich in inorganic salts such as calcium and iron, which are higher than those of eggs and fresh duck eggs, and are good foods for supplementing calcium and iron in summer.
But when cooking soup, people often use eggs and seldom use duck eggs. This is because duck eggs stink easily when used directly for cooking. So people are more willing to choose eggs at this time.