Mysterious "skull" pattern appears on preserved eggs? How did the strange "pine flower" pattern form?

There is a long-standing rumor that a peasant woman left her preserved egg ashes outside her house, which were mixed with the ashes of bones from the tall chimney of the crematorium. As a result, when the preserved eggs were opened and eaten, they were not pine flowers but "skulls"! Is it possible? Anyone with a little knowledge of chemistry knows that it can only be pine flowers. Chongqing Yongchuan, which is famous for its abundant production of pine flower preserved eggs, has the best say on this! Of course not!

Image source: Pixabay

So where does the "pine flower" on the preserved egg come from? Its main component is magnesium hydroxide hydrate formed after a series of chemical reactions during the pickling process of the preserved egg [1]. Speaking of magnesium hydroxide, some people may ask if magnesium hydroxide is edible? In fact, the solubility of magnesium hydroxide in water is very low. After entering the digestive system, it can react with gastric acid to form magnesium ions. Magnesium ions are an indispensable trace element in the human body. They have many functions such as activating enzyme activity and participating in protein synthesis. So the "pine flower" on the preserved egg can be eaten.

Where does the magnesium hydroxide hydrate on the “pine flower” come from? This brings us to the chemical reactions during the pickling process of preserved eggs. The pickling of preserved eggs generally goes through four processes: clearing, coagulation, color change, and maturation. This involves many chemical reactions. The formation of “pine flower” is just one of the chemical reactions. Usually, the pickling environment of preserved eggs is a strong alkaline environment. The eggshell contains magnesium carbonate and magnesium phosphate[2]. During the pickling process, magnesium ions gradually transfer from the eggshell to the egg white. They form magnesium hydroxide hydrate on the surface of the preserved egg white in a strong alkaline environment, thus forming a beautiful “pine flower” pattern on the preserved egg white.

Therefore, the "pine flowers" on the preserved eggs can never be replaced by the "skull". Its main ingredient is magnesium hydroxide hydrate, which not only increases the "appearance" of the preserved eggs, but also provides magnesium ions, a trace element for the human body. You can eat it with confidence!

[1] Cheng Jing, Li Lichan, Chen Xu, et al. Mechanism of gel and flavor formation during preserved egg processing[J]. Food Industry Science and Technology, 2024, 45(5): 357-366.

[2] Peng Zixin, Zhong Ruiqin, Wang Zhengjie, Jiang Hong. Ginseng paste and pine flower green: the secret of preserved eggs[J]. University Chemistry, 2023, 38(4):143-150.

Source: Chongqing Science Writers Association

Author: Jiang Xuefei, deputy chief physician, Peng Dan, laboratory technician, and Zou Jingbo, chief technician, Chongqing Yongchuan District Center for Disease Control and Prevention

Audit expert: Li Hanbin

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