A series of articles recently addressed the issue of a green pigment sometimes seen in bacon. The explanation of the phenomenon can be found in a Chemistry World article published in April 2012 by the Royal Society of Chemistry.
A team of researchers at the Univ. of Oklahoma found that nitrite, which has been used for centuries to preserve meats and ensure the safety of foods, causes the coloration. George Richter-Addo and his team at OU found that nitrite reacting with myoglobin produces the green tinge, which the team called ‘nitrite burn’.
The original research is J Yi and G B Richter-Addo, Chem. Commun., 2012, DOI: 10.1039/c2cc31065a.