Because I can't link to this online, I am copying this from the July & August "Notes from Readers" edition of Cook's Illustrated (the single best cooking magazine on the market today).
I often see "no nitrates or nitrites added" bacon in the grocery store. How does this differ from regular bacon? E.W. New Orleans, LA.
Nitrite has long been a controversial food additive, with studies showing it forms carcinogenic compounds called nitrosamines when heated in the presence of proteins, like those in bacon. Regular bacon is cured with nitrite (NO2) or a virtually identical chemical, nitrate (NO3), both of which act as preservatives, though only nitrite has the potential to form potentially harmful nitrosamines. Bacon labeled "nitrate-or nitrite-free" on the other hand, is brined with salt, a bacterial lactic acid starter culture, and celery juice (sometimes listed as "natural flavor").
But here's the catch: Celery juice naturally contains a high level of organic nitrate, which is converted into the problematic nitrite by the bacteria in the starter culture and also by saliva during chewing. Despite this fact, it's technically correct to label the bacon "no nitrates or nitrites added," since the compounds are formed during production, not added as ingredients. The question is: How do the levels of nitrite and nitrate in uncured bacon compare with those in its cured counterpart?
When we fired up strips of our favorite supermarket bacon, Farmland Hickory Smoked, along with Farmland All-Natural Uncured Bacon ("no nitrate or nitrite added"), tasters found the sampled virtually identical in taste and texture. To quantify the nitrite and nitrate levels in these bacons, we sent three packages of each type to a lab for testing. For comparison, we also sent three packages of the Best Buy from our tasting of artisanal bacon, Applegate Farms Uncured Sunday Bacon (labeled "no nitrites added"). As we expected, all the of the bacons contained nitrite and nitrate and the nitrite levels were well withing U.S. Department of Agriculture guidelines of no more than 120 parts per million (ppm). But to our surprise, the uncured bacon actually had higher levels of nitrite than the cured meat: Farmland Hickory Smoked Bacon registered an average of 9.7 ppm nitrite (and 48ppm nitrate), while its All-Natural counterpart showed an average of 16.3 ppm nitrite (and 10.3 ppm nitrate). And the Applegate Farms Uncured Sunday Bacon averaged more than three times the level of regular bacon: 35 ppm nitrite (and nearly as much nitrate, at 44.3 ppm).
The bottom line: All bacon is likely to contain nitrite and nitrate, whether added at the outset or formed naturally during processing. If you want to avoid these compounds, you'll have to avoid bacon - and any other processed meats containing celery juice - altogether.