Classification of Animal By-products: Edible vs. Inedible

When an animal is slaughtered for meat, the muscle cuts – steaks, chops, fillets – account for only a portion of the animal’s total weight. The rest, often half or more of the live weight, consists of parts that don’t make it onto the primary meat counter. These are animal by-products, and how they are classified determines everything: whether they end up on a dinner plate, in a pharmaceutical factory, or in a leather goods workshop. The most fundamental classification divides all animal by-products into two categories – edible and inedible – and understanding this distinction is central to the science of by-product utilization.

What are animal by-products? 🔗

Animal by-products include all parts of a live animal that are not part of the dressed carcass – that is, everything remaining after the primary meat cuts are removed. The meat industry is estimated to produce around 150 million tons of edible and inedible by-products per year globally. These are not waste materials. When properly classified, processed, and utilized, they generate significant economic value and reduce the environmental burden of animal processing. By-products may represent up to 75% of an animal’s live weight, but in their unprocessed state may be worth as little as 10-20% of the animal’s total value – yet with appropriate processing, the revenue from end products can nearly equal that of the meat itself.

The two primary categories: edible and inedible 🔗

Shortly after slaughter, animal by-products are separated into edible or inedible parts. The edible portion accounts for approximately 55% of by-product production, while the remaining portion is regarded as inedible. This separation is not arbitrary. It is based on food safety standards, regulatory requirements, cultural norms, and the condition of the material at the time of processing. In the United States, animal by-products are formally classified as hides, edible offal (including variety meats), and inedible offal.

Edible by-products 🔗

Edible by-products are parts of the slaughtered animal that are safe and suitable for human consumption, either directly or after processing. Typical edible by-products include liver, lung, heart, tongue, kidney, brain, spleen, blood, tail, ears, and mechanically recovered meat – all of which represent a good income for slaughterhouses while also contributing relevant nutrients to the human diet. These parts are collectively referred to as offal or variety meats.

Red offal and white offal 🔗

Within the edible category, a further distinction is commonly made between red offal and white offal. Edible offals are termed red offals in many contexts – for example, liver, heart, kidney, tongue, and sweetbreads – while white offals include lungs, pancreas, and esophagus. Most scientific publications focus on the chemical composition of red offal, whereas information on white offal – lungs, brain, stomach, and intestines – is less commonly found. Red offals are generally more sought after for direct human consumption, while white offals are more commonly used as food ingredients or processed into secondary products.

Nutritional value of edible by-products 🔗

Edible by-products are often nutritionally superior to ordinary muscle meat. Most organ meats are more nutrient-dense than muscle meat – particularly rich in B-vitamins such as vitamin B12 and folate, and in minerals including iron, magnesium, selenium, and zinc, as well as fat-soluble vitamins like A, D, E, and K. The protein content of edible by-products generally ranges from 15 to 22%, with liver, lungs, heart, and spleen presenting the highest protein concentrations. Liver, in particular, is widely recognized as one of the most nutrient-dense foods available – it is a concentrated source of vitamin A, B12, iron, and choline.

The utilization of edible meat by-products depends considerably on a number of factors such as culture, religion, income, and preference. All parts of edible meat by-products are salvaged and commonly used as human foods in South Africa, Egypt, Italy, Spain, and Asian countries. For example, pork liver is used to produce pâté in Europe, while tails are used in soups and bouillons, and blood is used as an ingredient in black pudding, blood sausages, and blood tofu.

Inedible by-products 🔗

Inedible by-products are parts of the animal that are not destined for direct human consumption. This does not mean they lack value – quite the opposite. Most inedible animal by-products consist of hides, hair, horns, teeth, blood, fats, bone, ligaments and cartilage, feet, manure, trimmings, rumen contents, and glands. These materials feed into a wide range of industrial processes.

Elementary and secondary inedible by-products 🔗

Inedible by-products can be further divided into two sub-groups. Elementary by-products are collected directly after slaughter and include blood, bones, pancreas, intestines, hides and skins, hooves, and horns. Secondary by-products are derivatives obtained from elementary by-products and may include products like buttons, bone meal, insulin, cutlery handles, and gelatin. This two-tier structure helps processors systematically extract value from materials that would otherwise be treated as waste.

Industrial uses of inedible by-products 🔗

The range of industries that rely on inedible by-products is extensive. Hooves and horns are also used for adhesives, plastics, plant food, photo film, shampoo, lamination, wallpaper, and plywood. Hair can be used for air filters, brushes, felt, insulation, plaster, and textiles. Bone is used for charcoal, fertilizer, and glass. Hides from abattoirs are often exported globally for reprocessing and converted to leather through tanning agents for the production of shoes, clothing, and car seats.

A key process for inedible by-products is rendering – a combination of thermal and mechanical treatment that separates fat, protein, and water from raw materials. Inedibles are rendered into products such as meat and bone meal, poultry meal, hydrolyzed feather meal, blood meal, and animal fats. The rendering industry processes over 54 billion pounds of animal by-products annually in North America alone, with approximately 85% of rendered products used as animal feed ingredients.

Glands and organs harvested from slaughtered animals – such as adrenal, parathyroid, pituitary, thyroid, ovaries, pancreas, and testes – are responsible for many of the hormones and enzymes used in the medical field today, including epinephrine, oestrogens, progesterone, insulin, trypsin, and thyroxin.

Factors that determine the classification 🔗

The boundary between edible and inedible is not always fixed. Several factors can shift a by-product from one category to the other.

Cultural and regional practices 🔗

Classification of by-products depends on local culture, customs, and regulations – as a result, some products can be downgraded from edible to inedible. Chicken feet are a clear example: in many East and Southeast Asian cuisines, they are a prized food item, prepared carefully and sold at a premium. In many Western countries, however, they are classified as inedible and sent to industrial processing. Blood, bone, skin, and hide may be classified as animal foods depending on existing or acquired customs and traditions – for example, the Maasai people of Kenya traditionally drink blood obtained from live cattle.

Animal health and processing conditions 🔗

The condition of the animal and the hygiene standards of the processing facility directly determine edibility. Organs from a healthy animal slaughtered and processed under sanitary conditions can be classified as edible. The same organ from a diseased animal, or one processed under poor conditions, is automatically reclassified as inedible. Edible by-products must be adequately preserved because they are particularly prone to microbial contamination. This is why veterinary inspection at the slaughterhouse is a non-negotiable step before any organ is approved for human consumption.

Economic considerations 🔗

Market demand also plays a role. If there is no local demand for a particular edible by-product, processors may redirect it to industrial uses simply because that is more economically viable. In the EU alone, more than 20 million tonnes of animal by-products are produced each year from slaughterhouses and food industries, yet some edible by-products are still being wasted due to market and supply chain constraints. This economic flexibility means the classification system is dynamic – it responds to changing consumer preferences, trade markets, and processing capacities.

Processing technology 🔗

Advances in food technology are continuously expanding what can be classified as edible. Improved cleaning methods, controlled-temperature processing, and new preservation techniques are making it possible to safely prepare by-products that were previously considered too difficult or risky to handle. Technologies have been developed to capitalize on the production of edible materials from normally inedible products, such as protein concentrates from horns and hooves for use as flavoring agents.

Why correct classification matters 🔗

Getting the classification right has practical consequences across multiple dimensions. From a food safety standpoint, edible by-products must meet the same regulatory standards as conventional meat – proper inspection, cold chain management, and facility hygiene are all mandatory. Gelatine, one of the better-known uses of edible by-products, is a protein extracted from the bones, skin, and ligaments of pigs and cattle, used as an ingredient in sweets, marshmallows, baking, soups, broths, sauces, shampoos, and medicine capsules. Misclassifying an inedible material as edible – intentionally or accidentally – creates serious public health risks.

From an economic perspective, when processed efficiently, offals can represent 15-20% of an animal’s total economic value, making correct classification and utilization essential to the financial viability of meat processing operations. Environmentally, proper classification enables near-complete utilization of the animal, reducing landfill burden and minimizing the environmental footprint of livestock processing.

What do you think? Given that the edible or inedible status of a by-product can shift based on culture, processing conditions, and economics, should there be a universal global standard for classifying animal by-products – or does regional flexibility serve the food system better? And as processing technology continues to advance, which currently inedible by-products do you think hold the most potential to become accepted food ingredients in the future?

References

1. https://meatscience.org/TheMeatWeEat/topics/raising-animals-for-meat/article/2015/11/20/what-are-animal-byproducts
2. https://www.mdpi.com/2071-1050/9/7/1089
3. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/animal-byproducts
4. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/inedible-offal
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC11174546/
6. https://www.healthline.com/nutrition/organ-meats
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC4597865/
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC8127651/
9. https://www.academia.edu/27493575/ESSENTIAL_RENDERING_All_About_The_Animal_By_Products_Industry
10. https://agric4profits.com/general-classification-of-animal-products/
11. https://www.foodunfolded.com/article/are-edible-animal-by-products-being-wasted
12. https://pmc.ncbi.nlm.nih.gov/articles/PMC9736461/