Volume 13: Industry Processes and Controls
6. Rendering
Processes involved in rendering in 1986
Raw materials for rendering
Manufacturing processes
Purchase of greaves for further processing

6.17 Rendering involves crushing animal by-products (eg, fat, bones and internal organs), heating them to drive off the water content (which can be as high as 65 per cent by weight) and then separating the residue into fat (generally called 'tallow') and solids (known as 'greaves').

6.18 There are different grades of tallow, the grading depending on the concentration of 'free fatty acid (ffa), colour, and general appearance, moisture and dirt content'. ¹ The single most important factor in determining grading is colour. Tallow of the highest calibre or 'good colour' tallow is used for soap manufacture and for human consumption, while the lower grades are used for animal feeds and fatty chemicals. ² The greaves were used in fertiliser or animal feed, or were processed further by pressing, centrifugation or solvent extraction to remove more tallow. After this further processing, the residue could be ground to produce MBM, which was used largely in animal feed, including pet food.

6.19 This section looks first at the types of raw material that were used by the rendering industry, and from where and how they were delivered to the rendering plant. Next, it describes the two main types of rendering, batch and continuous, and the solvent extraction process, which are important because of the interest in how these processes might have affected the BSE agent.

Raw materials for rendering

6.20 Renderers deal exclusively either with red meat material such as cattle, sheep and pig, or with poultry material. The term 'MBM' refers to meal produced from red meat animals, not poultry, so the renderers referred to in this chapter are only those processing non-poultry material.

6.21 In 1986, the material processed by renderers mostly came from slaughterhouses, and consisted of the parts of animals that were unsuitable for food or that people in the UK chose not to eat, such as:

• offal that did not have any more valuable use, such as the bladder, diaphragm and udder, as well as some intestines, kidneys, spleen, blood, stomach, heart, liver and lungs, which were only occasionally used for other purposes;
• the head, hooves, bones and tails;
• edible fat; and
• carcasses condemned as unfit. ³

6.22 Material from other sources accounted for 10 per cent or less of the raw materials used by renderers. ⁴ This included:

• whole carcasses of fallen stock from farms, kennels, veterinary sources (pets), and zoo animals such as antelope or giraffe; and
• waste from knacker's yards, and from other animal by-product trades such as hunt kennels, maggot bait farms, tripe dressers and tanneries.

6.23 In addition, renderers received waste fat and bones from butcher's shops, from food factories, and from boning-out and pre-packing operations supplying supermarkets.

6.24 Renderers could be categorised depending on the types and grades of animal material they processed. Therefore, this material was often sorted at the slaughterhouse before collection. The four main categories were as follows:

Technical rendering

The principal ingredient in technical rendering is low grade (green) offal and condemned material obtained from slaughterhouses, and other low grade material which may contain fallen stock (or parts thereof) from knackers and hunt kennels. The tallow is used for industrial purposes, including lubricants, and some in animal feed. The meat and bone meal produced by renderers is used in animal feed rations and pet food.

Rendering to produce high grade tallows

The raw material is the fresh fat and bones obtained from slaughterhouses, cutting plants and butcher's shops. The tallow may be used for high quality toilet soap, for further refining, bleaching and deodorising for use in food manufacture, catering etc. Animal protein [MBM] is used in animal feed.

Edible rendering

There are a number of plants which utilise fresh kidney suet and channel (opening) fats for direct human consumption. The raw materials are usually processed at lower temperatures to produce beef dripping for frying and 'premier jus' for packet suet and food manufacture. The greaves may be used in the manufacture of pet foods.

Specialist plants

There are a small number of plants which specialise in processing blood, feathers and poultry material. The products are used in animal feed and pet food. ⁵

6.25 A description of the further processing of tallow can be found in Annex A to this chapter.

6.26 Some renderers would therefore arrange with the slaughterhouse or gut room contractor to separate out certain material from the rest. ⁶ Other renderers operated gut rooms themselves. Any material not separated for renderers with specialised requirements would be thrown into a common skip to go to a renderer of low-grade, cheaper material. However, even among this low-grade material, the inclusion of stomach and intestine contents was discouraged by renderers:

The presence of stomach contents in intestines is much discouraged by renderers and always has been because of - I was going to say low-yield, non-yield, from such material, and because of its effect upon the colour of tallow produced. ⁷

This operation was all done in the in-house gut rooms. It was how well they operated as to whether there was any, or any stomach contents got into the rendering skip. But yes, we actively discouraged it. ⁸

Unfit meat and offal

6.27 Slaughterhouses sent most carcass parts that were unfit for human consumption to a renderer, in accordance with the Meat (Sterilisation and Staining) Regulations 1982. ⁹ The rendering process could be expected to ensure this material was 'sterilised' in the sense understood by these Regulations. For the reasons given in Chapter 1, such sterilisation was not capable of destroying the BSE agent.

6.28 Knackers sent carcass parts to renderers. Material from knackers was by definition unfit for human consumption, and therefore renderers of edible material did not accept knackery material. Certain classes of unfit material and knackery material were required to be stained before they could go to renderers, to prevent them from entering the human food chain. In practice, however, the majority of unfit material received by renderers was unstained. ¹⁰ Some renderers of inedible material refused to accept unfit material. However, those that did accept it did not have to handle it any differently from fit material, because their products were not for human consumption. ¹¹

Transport

6.29 Most rendering companies collected the material from slaughterhouses in their own vehicles. Some renderers, however, engaged contractors to do this. These contracting collectors mostly removed waste from butcher's shops and small slaughterhouses, often consolidating small collections of similar materials. Material was transported either directly to the rendering plant, or to a renderer's collection centre for consolidation and onward transport to the plant. ¹²

Arrival at rendering plant

6.30 Upon arrival at the rendering plant, the raw material would be weighed on a weighbridge, then either stored in the container in which it arrived, dumped into reception pits, or simply unloaded onto the floor in open bays.

6.31 As noted above, the raw material from slaughterhouses was sorted before it left the slaughterhouse. Hence material could usually be rendered as a batch on arrival at the plant, although there might be some rough redistribution to preserve a desired balance in the material being used for a batch. In reference to the undesirable inclusion of stomach contents in a load of material, Mr Bill Bacon of the UK Renderers' Association (UKRA) said: 'If a load arrived and you had stomach contents in it, you could not or you did not turn it away. You made a great noise about it the following day.' ¹³ A renderer specialising in edible tallow would only process a limited range of raw materials, and so would be more concerned about the content of a load than would one processing low-quality material into inedible tallow.

Manufacturing processes

6.32 The different rendering processes are described in Annex B to this chapter, as are the variations in processing time and temperature. All can be classified as either batch systems or continuous systems. As the names imply, in the former, material is cooked a batch at a time, while in the latter, raw material is fed in continuously at one end of the cooker and the finished product ejected at the other.

6.33 Batch rendering systems were used exclusively until the 1970s, when the first continuous rendering systems were introduced in the UK. As can be seen from Figure 6.4, the popularity of the various types of continuous system grew rapidly until the mid-1980s, by which time they were being used to produce at least 75 per cent of MBM in the UK. It has been suggested that the reduction in the use of batch rendering in favour of continuous rendering could have caused or contributed to the emergence of the BSE epidemic. This suggestion was made because the first identified cases of BSE were thought to have resulted from exposure to the disease in 1981/82, shortly after the time that continuous rendering became the primary method of rendering in the UK. ¹⁴ This issue is considered below under the heading 'Rendering, and inactivation of BSE' (paragraphs 6.45ff).

Figure 6.4: Proportion of MBM produced by plants using a continuous rendering process, 1971-88

• the energy crisis in the 1970s dramatically raised the price of solvents;
• the price of tallow fell relative to MBM in the late 1970s, reducing the profit in producing more tallow and less MBM;
• animal feed manufacturers began to produce higher-fat feeds, with about 10 to 12 per cent of fat, and no longer required the low-fat MBM produced by solvent extraction preferring higher-fat MBM instead; and
• the use of solvents entailed a risk of fire and explosion. ¹⁵

6.37 The proportion of MBM produced in the UK that was subjected to the solvent extraction method is not clear, as there are no authoritative statistics on this point. Mr John Wilesmith collated figures for Great Britain from the mid-1960s to the mid-1980s, which are set out in Figure 6.5. Witnesses from the rendering industry, however, said that the use of solvent extraction was never particularly widespread and that at no time was more than 50 per cent of MBM produced and used in the UK solvent-extracted. ¹⁶

6.38 According to MAFF figures, a number of plants stopped using solvent extraction during the 1970s, and two large plants (together producing 26 per cent of rendered material) stopped in 1980/81. However, at least 27 per cent of plants carried on using the solvent extraction process after that time, and at least one plant, in Scotland, was still using the process in 1992.

Figure 6.5: Proportion of MBM produced using solvent extraction, 1964-88

Source: Veterinary Record, vol. 128, 2 March 1991, p. 201

6.39 With the decline of solvent extraction, the secondary extraction of tallow from the solid greaves is now usually done with a press, ¹⁷ producing MBM with a fat content in the order of 10 to 14 per cent. ¹⁸

6.40 As with the shift from batch to continuous processing, the decline in the use of solvent extraction in the late 1970s has been suggested as a contributing factor in the emergence of the BSE epidemic. This is also considered below in the section on 'Rendering and inactivation of BSE'.

Purchase of greaves for further processing

6.41 When solvent extraction was common, small rendering plants often concentrated on the production of tallow, selling their greaves to other processors for further processing and grinding. The Inquiry did not receive comprehensive statistics on the size of this trade. By 1970 about half of the greaves being solvent-extracted by PDM were said to have been purchased from other renderers. ¹⁹ The greaves were bought from both inside and outside the UK. ²⁰ A 'very high proportion' of William Forrest & Son's greaves was imported from Northern Ireland. When the expensive solvent extractors were later phased out in favour of the more affordable presses, smaller renderers could afford to undertake the secondary processing of greaves themselves. ²¹ After the early 1980s, PDM's purchases of greaves from renderers outside its group were described as 'sporadic'. ²² Nevertheless, the practice continued. ²³

6.42 A renderer purchasing greaves from another renderer could not be absolutely certain of either the nature of its source material or the processing standards of the vendor.

Comparison of the UK rendering process with that of other countries

6.43 A comparison of rendering processes is set out in Annex C to this chapter. This is of interest when considering why BSE emerged in this country but not elsewhere. Unfortunately, information on processes used in different plants and details of the timing, temperatures and pressure used in other countries are difficult to obtain. The information we have gathered is therefore not comprehensive, and it is difficult to make exact comparisons.

6.44 However, similar changes to those experienced in the UK, both in the structure of the rendering industry and in the processes used, were seen throughout Europe and the United States. In particular, a movement away from solvent extraction seems to have been a common factor worldwide, and certainly the main equipment manufacturers sold their models throughout the world. ²⁴

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¹ YB92/06.00/9.3

² M12A tab 1 p. 17; YB89/06.06/7.3

³ Journal of the Society of Leather Technologists and Chemists, vol. 88, p. 71; S33 Rogers para. 17, S37 Foxcroft paras 43, 44

⁴ S37 Foxcroft para. 43; S33 Rogers para. 17

⁵ IBD1 tab 11, para. 2.4.4

⁶ T20 p. 78

⁷ T19 p. 91 - Mr Brian Rogers, Chairman of the UK Renderers' Association (UKRA)

⁸ T19 p. 92 - Mr Bill Bacon, UKRA

⁹ L17 tab 15

¹⁰ T60 p. 89 - Mr Paul Foxcroft, Prosper De Mulder

¹¹ T19 pp. 77, 79

¹² Animal Waste: A report on the supply of animal waste in England and Wales and in Scotland, paras 2.31-2.33, (M4 tab 3)

¹³ T19 pp. 91-3

¹⁴ J W Wilesmith et al., 'Bovine spongiform encephalopathy: Epidemiological studies', Veterinary Record, vol. 123, 17 December 1988, p. 638

¹⁵ S35 Bacon para. 17

¹⁶ S35 Bacon para. 17 and S33A Rogers para. 3 (4)

¹⁷ Animal Waste: A report on the supply of animal waste in England and Wales and in Scotland, para. 2.52 (M4 tab 3)

¹⁸ YB88/2.29/1.1

¹⁹ S37 Foxcroft para. 17

²⁰ T20 p. 94

²¹ Animal Waste: A report on the supply of animal waste in Great Britain, para. 2.36 (M4 tab 1)

²² T20 p. 92 - Mr Paul Foxcroft

²³ Animal Waste: A report on the supply of animal waste in England and Wales and in Scotland, para. 2.49 (M4 tab 3)

²⁴ S37 Foxcroft para. 31