Meat by-products, often referred to as the “fifth quarter” in the context of red meat processing, encompass
all edible and inedible parts of a slaughtered animal other than the dressed carcass (Toldrá et al.,
2012). The classification of these materials is generally dichotomized into edible and inedible categories,
a distinction heavily influenced by cultural norms, regulatory frameworks, and processing capabilities.
Edible by-products typically include organs such as the liver, heart, kidneys, tongue, and stomach (tripe),
as well as blood and certain fats (Irshad and Sharma, 2015). Conversely, inedible by-products comprise
hides, skins, hair, horns, hooves, teeth, and contents of the gastrointestinal tract. However, the boundary
between these categories is fluid; advancements in processing technology increasingly allow for the
recovery of edible proteins and functional compounds from materials previously deemed inedible waste
(Mora, Reig and Toldrá, 2014).
The volume of by-products generated is substantial, often constituting between 60% and 70% of
the slaughtered animal’s weight depending on the species (Irshad and Sharma, 2015). For instance,
in bovine processing, the dressed carcass yield is approximately 50–60%, leaving nearly half of the
animal’s mass as potential by-product material. This immense volume represents a critical reservoir of
biological material that, if mismanaged, becomes a significant environmental liability rather than an
economic asset.