UKRA - The United Kingdom Renderers' Association
What is the Rendering Process
In its simplest terms, the rendering process is a cooking and separating process that uses animal and poultry
by-products to produce purified fat and protein products. These inedible portions of animals are cooked at high
temperatures to remove moisture, kill bacteria and separate out the fat and protein. The result is a protein
rich meal and a useful fat portion.
Rendering involves the processing of those parts of meat animals that are not used for human consumption. Those
parts include the head, feet, bones, intestines, blood and various other tissues, which we cannot or choose not
to eat. Processing involves the crushing or grinding of the raw material, followed by heat treatment to reduce
the moisture content and kill micro-organisms.
All rendering plants contain some or all of the following process steps and the figure below shows how
they fit together in the overall plant.
- Raw Material Reception - This is where the incoming raw materials enter the facility and is
usually characterized by some form of double door to provide an odour lock to prevent the release of odours
during unloading operations.
- Storage and Handling of Raw Materials - Raw materials are stored for the minimum length of
time to keep them as fresh as possible. Usually they will be stored in lidded hoppers which have odour
extraction and control fitted to them. To comply with animal by-products regulations rendering facilities need
to keep accurate records of what raw materials are received, when they are received and when they are
processed. Rendering plants also keep their own internal logs of raw materials and their condition so that the
production schedule is arranged so as to minimise degradation of materials.
- Size Reduction of Raw Materials - Before being passed into the rendering process the raw
materials are reduced in size. This is important in allowing accurate heat transfer during the rendering
process which ensures that all parts of the rendered materials receive sufficient treatment to fully sterilise
- Processing of Materials - The crushed raw materials are heated in the rendering plant, of
which almost all in the UK are continuous units. The rendering equipment will produce a defined temperature and
residence time that will achieve sterilisation of the raw materials. All rendering plant is checked and
validated by DEFRA to exacting European standards before it can receive an operating license.
- Treatment of Odorous Emissions - Because it deals with natural by-products (some of which
may be quite old before they are even sent to the rendering plant) rendering does produce odours. All plants go
to great lengths to fit odour capture and extraction equipment and to fit effective odour abatement equipment.
In the past few years many UK rendering plants have spent several hundreds of thousands of pounds fitting
thermal oxidisers to give the best possible destruction of captured odours.
- Storage of Processed Materials - After rendering the meal and fat are separated and stored
prior to being dispatched off the site.
- Washing and Cleaning - Vehicles delivering the animal by-products, processing equipment and
the general rendering plant building all require regular washing and cleaning. Plants aim to minimise the
amount of water used, and effluent produced, by having policies on housekeeping and spill procedures that use
dry cleaning as far as possible; they also design their equipment and operations to be as leak proof as
- Effluent Treatment (on site or to discharge) - The washing and cleaning operations produce
effluent. The rendering operation itself also produces quantities of water that is driven off the product
during rendering. Some plants pass this water vapour through the thermal oxidiser directly but others condense
out the majority of the water first. All effluent produced is either treated in an approved process on site or
sent off site for treatment at a suitable treatment works.
- Process Flow Diagram -