Edible, inedible, low temperature, high temperature rendering, fat melting, tissue processing and gel bones – an overview of different processes and products
Animal fats that are sold as food, for example, must be treated and processed in the same way as food. This includes maintaining a cold chain and ensuring consistent hygienic conditions. Animal fats used in pet food are now subject to process and handling requirements that are just as stringent as those for food.
However, not all raw materials are suitable for use as food or pet food. Nevertheless, they contain valuable fats that are ideal as feedstock for biofuels or other industrial applications. For such applications, hygiene requirements, for example, are significantly lower. However, depending on the quality of the raw material, the application, and the type of by-products to be processed, higher processing temperatures and, in some cases, different equipment and process setups may be required.
GEA offers expertise in centrifugal separation technology - decanter centrifuges and high-speed separators - as well as evaporation technology for all rendering and fat-melting processes, as well as for gel bones and tissue processing.
What is rendering?
Rendering is the process for the production of:
- tallow
- lard
- poultry fat
- greases for oleochemicals, feed, and industrial applications
- fats to be used as feedstock for biofuels
Rendering uses heat and pressure to break down animal tissues, such as leaf fat, kidney and bacon fat, fat cuttings, but also bones and / or fallen animals. As the fat melts, it separates from:
- water
- proteins (i.e. “cracklings” or „greaves“)
- connective tissue
The melted fat is then purified and can be used as food, pet food, feed, biofuel, in cosmetics or industrial applications.
Wet Rendering
Also called “low temperature rendering".
Typical temperature: below 100 °C.
Method: Raw materials are cooked slowly at a temperature below 100 °C. Due to the overall lower process temperatures wet rendering produces stickwater which is evaporated in a separate evaporation stage.
Wet rendering with one decanter stage
When to go for wet rendering
Choosing the right process always depends on the quality or the raw material and how you intend to use the final products. Generally speaking, wet rendering produces higher-quality fats and proteins of better functionality than dry rendering. This is primarily due to the lower temperatures.
- Higher product quality: Produces lighter‑colored, more stable fats
- Less oxidation: Preserves natural fatty acid profile
- Better protein quality in by‑products: protein meals remain more digestible so that they can also be used for example as pet food ingredients
GEA scope for wet rendering
- 3-phase decanter centrifuges to separate the fat from the stickwater and solids, stand alone or installed on a skid
- Centrifugal separators to polish the fat, stand alone or installed on a skid
- Evaporators for stickwater evaporation
If the extracted fats and proteins are to be used exclusively for food applications, fat melting plants are the best option for which GEA can offer entire process lines.
Dry Rendering
Also called “high temperature rendering”.
Typical temperature: 115–145°C (sometimes higher).
Method: Raw materials are heated quickly - often under pressure - without added moisture, causing rapid breakdown and moisture evaporation. The high temperatures are required to inactivate any kind of bacterial activity.
Dry rendering with fat polishing
The high temperature vaporizes the water contained in the raw material so that there are only protein and fat that have to be separated by the decanter centrifuge. So, in many cases high temperature rendering does not require an additional separator for fat polishing.
However, if the quality requirements for the extracted fats are very high an additional disk-stack separator is the best choice to polish the fat.
When to go for dry rendering
Dry rendering is often the only viable option if the quality of the raw material allows nothing but high temperature treatment. Those raw materials are the perfect feedstock for biofuels or industrial applications.
In dry melting processes, these raw materials are safely and efficiently processed into valuable resources. They are
- Very efficient
- Less complex in their process setup
- Very effective: High heat destroys pathogens
- Often required for non-edible fats, particularly due to the raw material quality
- Best used for: biofuels, industrial-grade fats.
GEA scope for dry rendering
- Decanter centrifuges in 2-phase design for the separation of fats and proteins
- High speed separators for fat polishing
Fat melting – for high quality animal fats used for food and cosmetics
Fat melting plants produce high quality edible fats, cosmetic-grade tallow or pharmaceutical-grade raw materials. They focus on gentle heating and mechanical separation, ensuring that high‑quality raw fat can be removed efficiently without degrading the material.
Typical temperature: below 100 °C
In this process, the goal is generally to keep the temperature as low as possible in order to minimize any adverse effects on the quality of the obtained fat. For this reason, the process temperature during fat melting is typically set at the fat’s melting point. This has of course also a positive effect on the overall energy costs.
Fat melting process line
The process design varies depending on customer requirements and ultimately the intended use of the obtained fat. For example, a three-stage process in which the greaves are defatted can also be considered. This requires an additional decanter centrifuge but improves the overall yield of the process as well as the quality of the greaves.
In case the raw material is very high in protein even an evaporator for the stickwater can become feasible in order to recover the protein phase.
GEA Scope for fat melting plants:
- The design and engineering of the entire process line from grinder to the clarified fat tank after separator, including the supply of the necessary equipment for all process stages
- 2-phase as well as 3-phase decanters, depending on the desired process setup
- Centrifugal separators to polish the edible fats
- Evaporators for stickwater evaporation
