The color comes from a complicated reaction of the meat with preserving ... the other characteristics of cured beef.

Saltpeter( Potassium Nitrate) is added as part of the "cure", which is what gives it its ... Because of the brining, this meat can be salty so it must be blanched before cooking.

This method entails the use not only of salt but also of potassium nitrate or saltpetre ... scathingly says in The River Cottage Meat Book, "Industrial curing, of hams and bacons in particular ...