Saltpeter

Before the advent of modern refrigeration, saltpeter was commonly used to cure meats. It stops the growth of bacteria, keeping meats like ham, bacon, and salami safe to eat for longer periods. Today, more refined curing salts, which may still contain nitrates, are used in place of raw saltpeter for health and safety reasons.

Saltpeter forms in places with a combination of organic material, nitrogen, potassium, and the right environmental conditions, such as in manure heaps or the soil of caves. Historically, it was harvested directly from such deposits, but now it's more commonly produced industrially through chemical reactions to ensure purity and consistency.

While saltpeter is useful, it needs to be handled with care due to its potential health impacts. Ingesting large amounts can be harmful, and its use in food processing is strictly regulated. The compound is generally considered safe in the small amounts used in food preservation, but the industry has moved towards using more direct forms of nitrates and nitrites for this purpose, under controlled conditions, to minimize health risks.

It's also beneficial as a plant fertilizer due to its high nitrogen and potassium content. Despite its historical significance, the direct use of saltpeter, especially in food, has declined in favor of safer and more regulated alternatives.