Nitric Oxide
Also known as NO, Nitrogen monoxide
The fleeting reactive gas, made from nitrite in the meat, that binds the muscle pigment to set cured colour, and the crossroads from which nitrosamines can also form.
Nitric oxide is the short-lived, restless molecule at the exact centre of cured colour. It is where nitrite stops being a salt and becomes a reaction. In the mild acid of the meat, nitrite turns first to nitrous acid and then to nitric oxide, which seeks out the iron at the heart of myoglobin and binds it to make nitrosomyoglobin, the raw pink of bacon and fresh salame. Heat then sets the protein around that bond into nitrosylhaemochrome, the stable pink of cooked ham that will not brown on the plate or fade in the light.
Its restlessness explains the cure accelerators. Ascorbate and erythorbate work by pushing nitrite down the path towards nitric oxide faster and more completely, which is why a cure with an accelerator fixes its colour more quickly, more evenly and more reliably, and why bacon in the United States must carry 550 ppm of one of them.
The same crossroads has a darker branch. The reactive nitrogen chemistry that yields nitric oxide can, under high heat and in the presence of certain amino compounds, instead yield nitrosamines, several of which are carcinogenic. This is the tension at the heart of modern curing: the very reactivity that gives cured meat its colour and safety is the reactivity that must be steered away from the nitrosamine route, by accelerators, by holding nitrite to the least effective dose, and by care with high-heat cooking. To understand nitric oxide is to understand both why cured meat is the colour it is and why its chemistry is watched so closely.