Since early March, the product notoriously known as “pink slime,” Beef Products Inc.’s lean finely textured beef, has come under an unprecedented amount of scrutiny from most everyone who eats. The ensuing debate has prompted many to question why ground beef packages containing the product are not labeled as such, or at the very least, why the ammonium hydroxide gas used to kill bacteria on the beef is not labeled as an additive or ingredient.

Which elements of food production get labeled and which go incognito, and why?

In the case of lean finely textured beef, the answer to that question involves taking a look at the rules surrounding particular substances in food production called “processing aids.”

Processing aids are substances used to aid food production, are not found at significant levels in the final product and have no “functional or technical effects” on the food. The wide-reaching category encompasses everything from organic acids in produce washes to dough strengtheners in frozen waffles.

In short, neither the U.S. Department of Agriculture (USDA) or the Food and Drug Administration (FDA) require food makers to list processing aids on labels, and a wide variety of processing aids are allowed in food production as long as each one falls within the guidelines of being “Generally Recognized as Safe,” a classification for ingredients often abbreviated as “GRAS.”

The FDA keeps lists of GRAS products, whether they are used as additives or processing aids. (Whereas processing aids are not identifiable in foods, additives are ingredients required on the label because they are found in the final product and technically alter it.) These GRAS lists include everything from salt to chlorine gas to ammonium hydroxide, the antimicrobial used to sanitize lean beef trimmings.

To better illustrate the role of processing aids in food production, the USDA cites the example of a compound called sodium silicoaluminate and its role in sausage. The seasonings found in some sausages may include sodium silicoaluminate for its technical use as an anti-caking agent. Look at that sausage as a whole, however, and the presence of sodium silicoaluminate does not significantly change the food’s identity as a sausage.

Given the complexity of the modern food system, accounting for every input that goes into the average supermarket product would be a challenging and largely impractical undertaking, said Dr. Richard Raymond, former undersecretary for food safety at USDA.

In theory, substances classified as processing aids should carry no distinguishable traits into the final product, and therefore identifying them all on a label should have little value, Raymond told Food Safety News. But the classification of processing aids is not an exact science, he added, and some processes get excluded from the club.

As an example, Raymond cited Congress’ classification of irradiation as an additive rather than a processing aid despite the technique fitting the criteria of a processing aid. Food irradiation is the process of eliminating microorganisms from food through exposure to ionizing radiation.

In the U.S., meats, spices and some fruits and vegetables can be irradiated to improve safety or shelf life. Because of irradiation’s classification as an additive, however, irradiated foods are designated with an international symbol, the Radura, to inform consumers their food was treated with irradiation.

“When consumers see the Radura symbol on meat, they don’t want to eat it,” Raymond said. “But (for) whole carcass, low-dose irradiation is no different from any other processing aid that’s generally recognized as safe.”

As it turns out, classifying additives and processing aids as GRAS is not an exact science, either. As the term “Generally Recognized” implies, the FDA looks for a substance to be considered safe according to the consensus of qualified experts, but the agency simply lacks the resources to test all ingredients itself.

Individuals in the food industry often supply scientific data to the FDA for the agency to declare an additive or processing aid as GRAS. Because of the sheer number of substances involved in food production, the FDA relies on industry to vet products and has not conducted a full review of GRAS substances since 1997.

As a result, industry perception plays a role in whether a substance gets declared as a processing aid or an additive, and therefore whether or not it ends up on the label. By the nature of the categorizing process, each substance gets classified on an individual basis, as the USDA’s federal food labeling guide explains:

“[The Food Safety Inspection Service] does not have a definition for incidental additives or processing aids. However, if a company believes that the use of a substance in the manufacture or formulation of a meat or poultry product is consistent with FDA’s labeling definition for an incidental additive processing aid, then data needs to be submitted to FSIS to substantiate conformance with the FDA regulation. FSIS will determine on a case-by-case basis whether a request for the specific use of an ingredient is consistent with FDA’s labeling definition of an incidental additive processing aid and thus, exempt from labeling.”

As the scrutiny around lean finely textured beef continues, the intricacies of food labeling rules are certain to only make the debate slimier.