McGee on nitrates/nitrites

The Red-Meat Miracle, and Other Tales From the Butcher Case. (NYTimes)

Then there’s the ongoing saga of nitrite and nitrate, which give hams, bacon, hot dogs, bologna and other salt-cured meats their special color and tang. Nitrite reacts in the meat tissue to form nitric oxide, which binds tightly to the iron in myoglobin and turns it a stable red. Nitrite is also toxic to many microbes, including the bacteria that cause botulism, so it’s a critical preservative in cured sausages. For centuries meats were treated with a liberal mixture of salt and saltpeter, or sodium nitrate, which bacteria on the meat converted into nitrite. Nowadays manufacturers generally use very small quantities of pure nitrite, or a mixture of nitrite and nitrate.

In the 1970s, the nitrite and nitrate in cured meats fell under the suspicion that they might cause cancer. Later research showed that we get far more of these chemicals from vegetables like celery, spinach and lettuce. Their abundant nitrate comes from the soil and is turned into nitrite by bacteria living in our mouths.