Historically, potassium nitrate (KNO₃)—known as saltpeter—was used to cure meat, as it was thought to improve the meat’s flavor, texture, and shelf life. But at the turn of the last century, German scientists discovered that it wasn’t nitrate that was responsible for these changes. Over time, nitrate (NO₃) converts to nitrite (NO₂), which then converts to nitric oxide (NO). Both sodium nitrite and nitric oxide are responsible for curing and preservation. Most important, they inhibit the growth of dangerous microbes such as Clostridium botulinum, the bacteria that causes botulism. Eventually, most commercial ham and bacon producers switched from nitrate to the intermediate form, sodium nitrite, cutting out the waiting period and saving themselves valuable time during processing.
In an ideal world, all nitrite would be converted to nitric oxide during the curing process. Any nitrite that remains can form carcinogenic compounds called nitrosamines when heated in the presence of proteins, such as those in bacon. To combat this problem, manufacturers often add another ingredient to the curing solution: either sodium ascorbate or its isomer (chemical mirror image), sodium erythorbate. These ingredients accelerate the process by which nitrite breaks down into nitric oxide, leaving less nitrite that can form nitrosamines in the finished product. The acceptable levels of all three additives (sodium nitrite, sodium erythorbate, and sodium ascorbate) are closely regulated by the U.S. Department of Agriculture (USDA) to keep bacon safe for consumption.