Century eggs, also known as pidan or thousand-year eggs, undergo a fascinating transformation during their preservation process. The black color is a result of chemical reactions that occur during the long aging period.
The Chemistry Behind the Blackening
The blackening of century eggs is primarily due to the interaction of hydrogen sulfide (H₂S) with iron (Fe) present in the egg yolk and white.
- Hydrogen Sulfide Formation: Bacteria present in the preserving mixture break down proteins in the egg, releasing hydrogen sulfide as a byproduct.
- Iron Sulfide Formation: The hydrogen sulfide reacts with the iron in the egg, forming iron sulfide. This compound is black and gives the egg its characteristic dark color.
Other Factors Contributing to the Blackening
While iron sulfide is the primary pigment responsible for the black color, other factors also play a role:
- Lead: Some traditional methods of preservation involve using lead-based compounds, which can contribute to the dark color of the egg.
- Alkaline Environment: The alkaline environment created by the preserving mixture also contributes to the chemical reactions that lead to the blackening.
Understanding the Process
The blackening of century eggs is a natural consequence of the preservation process. It's not a sign of spoilage but rather a visual indicator of the egg's transformation into a unique and flavorful delicacy.
