There are two main reasons for the blackening of mutton stewed in iron pot. When the meat is stewed in an iron pan, the iron element and the components in the mutton will undergo an oxidation reaction, resulting in a black surface of the mutton. This is because oxygen interacts with iron at high temperature to produce a compound called quinone. This compound will make the surface of ingredients appear dark brown or almost black. Improper seasoning time can also lead to mutton blackening. If seasonings are added at high temperature in advance and cooked for a long time, spices containing pigments and polyphenols, such as pepper and lobster sauce, will cause coking reaction in high temperature environment, making the surface of ingredients dim or even black.