Rendering: Process and Benefits in the Meat Industry

Every animal brought to slaughter yields far more than the cuts of meat on display at a butcher shop. Bones, fatty tissue, offal, blood, and trimmings – together, these by-products can account for nearly half the weight of the animal. Without a reliable system to process them, meat production would generate staggering amounts of waste and carry enormous environmental costs. Rendering is the industrial solution to this challenge. It is the process of converting animal by-products into stable, commercially valuable materials through the application of heat, pressure, and mechanical separation – producing fats such as tallow and lard, and protein-rich solids like meat and bone meal. Understanding how rendering works, which systems are used, and where the products end up is fundamental to appreciating how the modern meat industry operates sustainably.

What is rendering? 🔗

At its core, rendering is a thermal processing operation that simultaneously dries animal tissue and separates fat from bone and protein. The process yields two primary outputs: a fat commodity and a protein meal. Raw materials fed into a rendering plant include fatty tissue, bones, offal, and in some cases entire carcasses of animals condemned at slaughter or that have died during transport. Additional sources include butcher shop trimmings, expired meat from grocery stores, and restaurant grease. The most commonly processed animal sources are beef, pork, poultry, and mutton.

Rendering is broadly divided into two categories: edible rendering and inedible rendering. Edible rendering is essentially a meat-processing operation carried out at low temperatures – generally below the boiling point of water – to produce lard and edible tallow suitable for food use. Inedible rendering processes materials that are not suitable for human consumption for aesthetic or sanitary reasons, converting them into industrial fats and protein meals used in animal feed and manufacturing. Both types follow the same fundamental principle: apply heat, separate the components, and recover the value locked within the raw material.

Steps in the rendering process 🔗

While specific equipment and temperatures differ across systems, the overall sequence of operations in rendering is consistent across the industry.

Size reduction and pre-treatment 🔗

Before any thermal processing begins, raw materials must be reduced in size. Shredders, grinders, or crushers break the incoming material into smaller particles. The smaller the particles, the more efficiently heat penetrates the material and the more completely fat is released during cooking. This step also enables more uniform processing throughout the batch or continuous stream.

Cooking and fat separation 🔗

The ground material is then subjected to heat treatment inside a cooking vessel. The heat melts the fat cells, breaks down tissue, and drives off moisture. Once cooking is complete, the material undergoes separation to divide liquid fat from solid protein. In wet processes, the material is heated with added steam and then pressed to remove a water-fat mixture, which is subsequently separated into fat, water, and fine solids through centrifuging or evaporation. In dry processes, moisture is driven off as steam, and the released fat drains freely from the solids.

Pressing, drying, and grinding 🔗

After fat separation, the remaining solids – called cracklings or press cake – still contain residual fat and moisture. These are mechanically pressed to extract more fat, then dried to a low-moisture state. The dried solids are ground into meat and bone meal, a protein-rich powder used extensively in animal nutrition. The recovered fat undergoes further purification – filtration and centrifugation – before being classified and dispatched to end users.

Types of rendering systems 🔗

The rendering industry employs several distinct processing systems, each suited to different operational scales, raw material types, and end-product requirements. Choosing the right system depends on throughput capacity, energy availability, capital investment, and the quality specifications of the target market.

Wet rendering 🔗

Wet rendering involves cooking the raw material in the presence of water or steam. This method is particularly effective for processing fatty tissue and produces high-quality fats. In wet inedible rendering, the ground material is heated with steam, pressed to remove the fat-water mixture, and then separated through centrifuging or evaporation into fat, water, and fine solids. The solids are dried and ground into meat and bone meal. Edible wet rendering operates similarly but at lower temperatures and uses additional centrifugal separation stages to produce food-grade fats like lard and edible tallow.

Wet rendering is more energy-intensive because large volumes of water must be heated and subsequently evaporated. However, high energy costs in the 1980s popularised wet continuous processes because they allowed process vapors to be reused to pre-heat or dry incoming materials, improving overall energy efficiency. This system is best suited for processing fresh, high-fat raw materials where fat quality is the primary commercial objective.

Dry batch rendering 🔗

Dry batch rendering heats the raw material without any added water, relying entirely on the material’s own moisture content and the applied heat to drive the process. A typical dry batch system heats material to around 280°F for several hours at up to three atmospheres of pressure, although some units operate without pressurization. During cooking, water boils off as steam through a vent; once moisture is sufficiently removed, the temperature increases to break down animal tissues and release fat, which drains from the vessel. The remaining solids are removed and processed into meat and bone meal.

The dry batch process was invented in the 1920s, using horizontal steam-jacketed cylinders. Its claimed advantages over the earlier wet ‘tanking’ method included better energy economy, improved protein yield, faster processing, and fewer noxious odors. By the end of World War II, the dry batch process had become the industry standard for inedible rendering. Today, it remains well-suited to smaller operations and facilities processing mixed or variable raw material streams, offering flexibility and relatively low capital requirements.

Continuous dry rendering 🔗

Continuous dry rendering was introduced in the 1960s and has since largely displaced batch systems in high-volume operations. The key difference from batch processing is that a screw or rotating drum moves material through a steam-jacketed horizontal cylinder continuously, with throughput rates reaching up to 40 tons per hour and typical cycle times of two hours or less. The cooker is designed with distinct zones that facilitate sequential moisture evaporation and tissue breakdown, allowing steady-state operation once the system reaches equilibrium.

Continuous dry processes were introduced by The Dupps Company, one variant using a modified conventional dry cooker and another using a mincing and evaporation approach to dry the material and extract fat. Modern continuous systems often incorporate vacuum operation to enhance water removal and heat recovery mechanisms to improve energy efficiency. Their consistent output quality, lower labor requirements, and high throughput make continuous rendering the preferred choice for large-scale packer-renderer operations.

Continuous low-temperature rendering 🔗

Some rendering operations, particularly for edible-grade fats, use low-temperature continuous systems that rely on mechanical methods rather than high heat to separate fat and moisture from the raw material. These systems separate fat and moisture from material using mechanical methods, preserving fat quality by limiting heat-induced oxidation and off-flavor formation. This approach is standard for edible rendering, where the output is destined for direct food use or high-value cosmetic applications.

Products of the rendering process 🔗

Rendering generates two broad categories of commercial output: fat products and protein meal products. The quality and grade of each depends on the source material, the rendering temperature, and the processing system employed.

Tallow and lard 🔗

Tallow is the rendered fat from cattle and sheep; lard is the rendered fat from pigs. Both are produced in edible and inedible grades. Rendered fat is classified into categories – Category 1, 2, or 3 – depending on the source material, and this classification determines how it can legally be used. Edible-grade tallow and lard are used in food manufacturing, frying, and baking. Inedible grades are directed to industrial applications.

Meat and bone meal 🔗

Meat and bone meal (MBM) is the dried, ground protein fraction remaining after fat extraction. The product is rich in protein, calcium, and phosphorus, and is used extensively in animal feed, pet food, and fertilizers. Protein content in MBM typically ranges from 45 to 55%, making it a concentrated and cost-effective nutritional ingredient for livestock and aquafeed formulations. Blood meal, feather meal, and poultry by-product meal are additional protein outputs produced when specific raw material streams are processed separately.

Applications of rendered products across industries 🔗

The downstream market for rendered products spans a remarkable range of industries, which is precisely what makes rendering such an economically and environmentally significant process.

Animal feed and pet food 🔗

Animal feed is the single largest end market for rendered products. Category 3 rendered fat is mainly used as a feed ingredient in livestock feed, aquafeed, and pet food, where it provides preservative, nutritional, and binding properties. Meat and bone meal supplies concentrated protein and minerals to supplement grain-based feed rations, supporting growth rates and feed conversion efficiency in poultry, swine, and cattle production.

Food industry 🔗

Edible tallow and lard have long-standing roles in food processing. Lard is valued in bakery applications for producing flaky pastry textures and has a high smoke point that makes it effective for frying. Tallow was historically the dominant frying fat in fast food before being displaced by vegetable oils in the late 20th century. Both fats continue to be used in certain processed food formulations and are experiencing renewed interest in artisan food production.

Biodiesel and renewable fuels 🔗

Tallow serves as a feedstock in transesterification, the chemical reaction that converts fat into biodiesel. This application has grown substantially as governments in the European Union and North America have introduced mandates for renewable fuel content in transport energy. Animal tallow is increasingly attractive to renewable fuel manufacturers due to its availability, relatively low cost, and high cetane number – a measure of combustion quality in diesel engines. Lower-category rendered fats, which cannot be used in food or feed, are channeled into this energy recovery pathway.

Cosmetics, soaps, and industrial products 🔗

Higher grades of tallow are used in the production of soaps, lubricants, and the fatty acids required to manufacture cosmetics, paints, plastics, and detergents. Stearic acid derived from rendered fat is used as a processing aid in tire manufacturing and as an emulsifier and consistency agent in personal care products. The oleochemical industry converts rendered fats into glycerol and fatty acids – building blocks that appear in a wide range of consumer and industrial goods. Collagen extracted from animal by-products during processing is used to produce gelatin, which serves as a gelling agent in the food industry.

Fertilizers 🔗

Bone meal, blood meal, and other nitrogen- and phosphorus-rich rendering outputs are applied as organic fertilizers in both conventional and organic farming systems. These products release nutrients slowly as they decompose in soil, improving fertility and reducing dependence on synthetic nitrogen fertilizers derived from fossil fuels.

Why rendering matters: sustainability and economic value 🔗

The sustainability case for rendering is compelling. Without rendering, approximately 50% of each meat animal would go to waste, and the volume of material generated by the US meat industry alone would fill all landfills in as little as four years. By converting these materials into productive commodities, rendering prevents the generation of methane – a potent greenhouse gas – from decomposing organic matter in landfills. The rendering industry recycles 1.6 billion pounds of used cooking oils annually, converting them into biodiesel and renewable diesel.

The economic contribution is equally significant. The US rendering and meat by-product processing industry has grown at a compound annual growth rate of 6.0% over the past five years, reaching an estimated $8.3 billion in revenue in 2025. For slaughterhouses and meat processors, rendering converts what would be a waste disposal cost into a revenue stream, improving the overall profitability of meat production and keeping consumer prices lower than they would otherwise be. The development of industrial-scale rendering was primarily responsible for enabling the profitable utilization of meat industry by-products, which in turn allowed the meat industry to scale up and make animal protein more economical for consumers.

Regulatory oversight ensures that rendering remains safe. Standards set by bodies such as the US Food and Drug Administration and the European Union’s animal by-products regulations govern which materials can be rendered, at what temperatures, and into which product categories they can be directed. These rules are particularly strict regarding the use of ruminant-derived protein in ruminant feed – a precaution introduced following the BSE crisis of the 1990s – and they continue to evolve as the science of food safety advances.

What do you think? Given that rendering prevents roughly half of every slaughtered animal from going to waste, should more consumer-facing food and cosmetics labeling reflect the presence of rendered ingredients? And as biodiesel mandates grow, do you think the energy sector’s growing demand for rendered fats could create competition with the animal feed industry – and how should that tension be managed?

References

1. https://en.wikipedia.org/wiki/Rendering_(animal_products)
2. https://www.franklinmiller.com/applications/rendering
3. http://foodtechinfo.com/foodpro/index_gas_technologies/rendering/
4. https://mavitecrendering.com/about-rendering/
5. https://efpra.eu/rendered-products/rendered-fat/
6. https://bakercommodities.com/products/tallow/
7. https://buyofuel.com/blogs/animal-tallow-hidden-gem-industries/
8. https://www.targray.com/biofuels/feedstock/animal-tallow
9. https://www.sunriserendering.com/rendering-industry-understanding-the-process/
10. https://bakercommodities.com/blog/2022/01/15/rendering-organic-recycling/
11. https://www.ibisworld.com/united-states/industry/rendering-meat-byproduct-processing/5787/
12. https://www.fda.gov