Sodium chloride is not the only salt with an important role in salt-curing. The others were unpredictable mineral impurities in the rock, sea, and vegetable salts originally used for curing. One of these, potassium nitrate (KNO3), was discovered during the Middle Ages and named saltpeter because it was found as a salt-like crystalline outgrowth on rocks. In the 16th or 17th century, it was found to brighten meat color and improve its flavor, safety, and storage life. Around 1900, German chemists discovered that during the cure certain salt-tolerant bacteria transform a small portion of the nitrate NO3 into nitrite (NO2), and that nitrite rather than nitrate is the true active ingredient. Once this was known, producers could eliminate saltpeter from the curing mixture and replace it with much smaller doses of pure nitrite. This is now the rule except in the production of traditional dry-cured hams and bacons, where prolonged ripening benefits from the ongoing bacterial production of nitrite from nitrate.