Potassium Nitrate
Also known as Saltpetre, Saltpeter, Bengal saltpetre, E252, KNO3, Nitre
Potassium nitrate, the traditional saltpetre, the original curing salt now largely replaced by measured nitrite and standardised blends.
Potassium nitrate, saltpetre, is among the oldest preserving agents known to the kitchen. Scraped as a white bloom from the walls of stables and cellars or leached from nitre-rich earth, it was curing meat in China and in Rome long before anyone understood why it worked, and it gave the world its rose-pink hams and bacons for the better part of two thousand years. The same salt made gunpowder, which kept it valuable and, at times, strictly controlled.
For all that history, saltpetre does nothing to meat by itself. It is a reservoir. Nitrate-reducing bacteria in the meat convert it slowly to nitrite, and it is the nitrite that fixes the colour and holds back Clostridium botulinum. That is why saltpetre curing was always a slow, cool, patient business, and why it could betray the maker: the nitrite actually produced depended on the flora, the temperature and the time, none of them controlled, so a cure might come out grey and unprotected, or harshly over-nitrited if the reduction ran too far.
When it was shown in the early twentieth century that nitrite was the true active agent, the trade moved to measured nitrite and to standardised nitrate blends, which gave a reliable dose where saltpetre gave a guess. Potassium nitrate, additive E252, did not disappear. It is the nitrate carried in the European Salvianda salt, it survives in a number of traditional and protected recipes, certain dry-cured hams and regional sausages, and it is still sold to home curers who want to add a nitrate reservoir to a long southern-style dry sausage. In real terms it is used only in the small amounts a long cure needs, folded into the salt, never as a headline ingredient.
For the curesmith, saltpetre is both a link to the deep history of the craft, a reminder that colour and safety were won for centuries by feeding bacteria a reservoir and trusting time, and a caution. Used today it deserves more care than a modern cure, its unpredictability respected and never assumed to behave like the weighed nitrite that replaced it.