Sodium Nitrite
Also known as E250, NaNO2
Sodium nitrite (NaNO2, E250), the specific salt that carries nitrite into almost all modern curing, always diluted in a curing blend.
Sodium nitrite is the salt through which nitrite reaches most cured meat. It is a white, highly soluble solid, and it is the active 6.25 per cent of Cure #1 and of Cure #2, and the active 0.6 per cent of the European nitrited salts, the rest being ordinary salt. On its own it is never handed to a curesmith to weigh, both because the dose is too small to measure safely and because it is poisonous in the gram quantities that would be easy to spill; the pink dye and the dilution of the curing salts exist precisely to keep the pure salt out of untrained hands.
In the meat it is the source of the nitrite ion, and everything said of nitrite, the colour by way of nitric oxide, the guard against Clostridium botulinum, the cured flavour, is what sodium nitrite delivers. It is the additive numbered E250, and on a European ingredient label the cure in a ham or a sausage will usually appear as that number.
Its close relatives divide the field. Potassium nitrite (E249) does the same job and is used where sodium is to be limited. Sodium nitrate (E251) and potassium nitrate (E252) supply the slow nitrate reservoir rather than nitrite direct. In practice, for the great majority of cured products, sodium nitrite in a diluted curing salt is the agent, and the legal ingoing limits set out under nitrite are the limits that govern it.