Our industrial food production system, from a free market viewpoint, works very well. Large corporate farms are always looking for a way to add efficiencies (and in turn, pad the bottom line). Instead of tossing out scraps, they can be ground and re-sold as pet food. Or, they can be ground and sold as meat filler.
Meat filler is what ends up in fast food and school cafeteria hamburgers. It is not appetizing to think about, so try not to. If you stop at McDonalds at lunch, you are likely consuming the parts of a cow that would otherwise end up in your pet’s bowl (not that this is a terrible thing).
How do these plants sanitize meat filler? Aside from irradiation, they can also use ammonia. That is right; they inject the meat filler with ammonia on the assumption it will kill off pathogens like E. coli and Salmonella. This process is so foolproof that the USDA even exempted ammonia-treated products from pathogen testing (surprise, though: E.coli and Salmonella still show up).
Ammonia is a naturally-occurring chemical agent that is used in many commercial cleaning products, most notably window cleaner. The USDA believes that ammonia-treated products are safe for human consumption. They very well may be safe, but a recent New York Times article notes consumer complaints about the smell and taste of this beef.
And where is ammonia on the ingredient label? Beef producers asked for ammonia to be considered a processing agent, so they do not have to list it even though it was injected directly into the product.
For me, ammonia treatment is just another reason to skip commodity beef.