Carcass butchery
Carcasses are sold whole, or as sides, or may be cut into smaller ‘primal’
or ‘retail’ joints. The exact way a carcass is butchered into joints varies between countries, within countries and depending on the particular use that may be made of the meat. Three ways of dividing up a side of beef into primal joints are shown in Fig. 4.5. These illustrate the variation between countries. In particular, in the French system, the carcass is cut into many more joints. This reflects the way retail joints in France are often based on individual, or small groups of adjacent muscles, dissected from others along the natural lines of separation between muscles. This allows inherent differences in the quality characteristics of different muscles, particularly tenderness, to be best exploited. In the systems used in the UK and USA, the differences in inherent quality are still recognized. For example the high value cuts of the loin and hindquarter (sirloin, rump, topside and silverside) are distinguished from lower value cuts such as those of the shoulder, brisket and flank, but the differentiation is less detailed. In the UK and USA, retail joints tend to be cut with less regard for differences between individual muscles, the cutting lines being across muscles rather than between them.
The smaller carcasses from pigs and lambs are cut into fewer primal joints. In the pig, after removal of distal ends of the legs, the carcass is cut into four main primal joints, the loin, belly, hind leg or ham, and the foreleg/shoulder. In North America the foreleg/shoulder is cut into the ‘butt’ and the ‘picnic’. An excellent account of the different cutting systems is given in Swatland (1994).
Fig. 4.5.Three methods of butchery of a side of beef into primal joints (based on information in Strother, 1975).
A major factor governing the design of modern slaughterplants is hygiene. The hygienic and other requirements are often laid down in legislation. In the UK, the requirements for the construction, layout and equipment of slaugherplants, meat cutting premises and cold stores are specified in The Fresh Meat (Hygiene and Inspection) Regulations 1995. These regulations also require the licensing of premises and give responsibility for ensuring compliance with hygiene, and animal and meat inspection requirements, to Official Veterinary Surgeons (OVSs) appointed by Central Government.
To maintain hygiene there must be clear separation of inherently dirty and clean areas, and the personnel who work in them. Therefore, the lairage and area up to the point of completion of bleeding is separated from subsequent areas to segregate live animals from carcasses and reduce to a minimum the chances of contamination of the clean areas. For the same reason, the entry of vermin, birds and insects, especially flies, must be prevented. Parts of the animal that are likely to be dirty, or potential sources of contamination, such as hides, skins, pelts, feet and guts need to be removed from the carcass dressing area as directly and quickly as possible. In poultry plants, stunning and bleeding, and scalding and plucking, should be carried out in separate rooms. Similarly, the evisceration of poultry must be in a separate room or at least in an area widely separated from other areas and partitioned off from them.
The lairage must be large enough to enable a sufficient reservoir of animals to be held while allowing a long enough resting period to recover from their journey from the farm or market. It must be provided with facilities for watering, and if necessary, feeding animals, and a pen with separate drainage to hold diseased or injured animals isolated from other stock. There need to be effective removal and disposal systems for the manure from the lairage.
The guts must be cleaned of their contents in rooms set aside for that purpose. There need to be rooms for the storage of hides and pelts, horns, hooves, fat and other waste material, and rooms for the prepara- tion and cleaning of offal. Hygienic facilities for the disposal of solid and liquid waste, and an adequate drainage system, are required.
Construction of the building must be appropriate. Floors need to be impermeable and non-slip, yet easily cleaned, walls impermeable and washable. All surfaces need to be impervious and easily cleanable with no areas that can retain dirt. Joints between walls and floors should ideally be rounded to facilitate cleaning. Equipment and fittings should be of durable, impermeable and corrosion-resistant materials such as stainless or galvanized steel or plastic. Wood is not acceptable.
Ventilation is important to provide good working conditions, prevent condensation and reduce the risks of contamination by aerosols. Even lighting with a minimum brightness of 220 lux in
working areas, and 540 lux where meat inspection is carried out, is required. It is important that the light does not distort normal colours.
There must be adequate lavatories and washing facilities for personal hygiene, adequate supplies of clean, wholesome (potable) hot and cold running water and cleaning facilities. There must be adequate facilities for disinfection of knives, tools and other equipment, and the cleaning and disinfection of vehicles delivering animals or transport- ing meat. People working in meat plants must not be suffering from any diseases that could be transmitted to others via the meat or equipment they handle, or have open (undressed) cuts or abrasions. They must wear protective clothing and footwear, cover hair and beards, and maintain personal cleanliness. Activities such as eating and smoking are unacceptable.
Sufficient and adequate refrigeration facilities must be available.
Within the EU, a Directive (64/433 EEC) specifies that all fresh meat that will be traded within the Union must be chilled immediately and kept at a temperature of +7°C or less for carcasses and cuts, and +3°C for offal. Frozen fresh meat must be maintained at !12°C or less.
Cleaning and disinfection
Plant and equipment hygiene is essential to the production of meat that is safe to eat. Two processes are necessary to achieve this. Cleaning removes dirt that could harbour or support the growth of micro- organisms. Disinfection kills remaining microbes, or at least reduces their numbers to safe levels. It may not kill bacterial spores, however.
Cleaning obviously has other benefits in improving the working environment and reducing the chances of contamination of carcasses and meat with other foreign matter. The cleaning process usually involves a combination of physical and chemical removal of dirt. It is therefore facilitated by scrubbing and hosing with water, often hot water and with the addition of detergents and other cleaning agents.
Although their main action is to remove fat and protein deposits (organic dirt) detergents also need to be effective against non-organic material, such as the scale formed from hard water, since in practice dirt is usually a combination of organic and non-organic components.
Important characteristics of detergents are surfactancy, or wetting power, dispersion and suspension. These characteristics enable the detergent to cover and penetrate the dirt, to break it up into small particles and to float these particles away from the surface. Alkaline detergents are very effective against organic dirt. They include caustic soda (sodium hydroxide), which is rather corrosive, and washing soda (sodium carbonate), which is less so. Acid detergents usually contain phosphoric acid and are particularly effective against non-organic dirt.
The most commonly used surfactants, or wetting agents, are anionic – forming a negatively charged active ion in solution. They are some- times mixed with non-ionic surfactants to improve the cleaning qualities in commercially available detergents. When used with hard water (containing high levels of dissolved calcium and magnesium salts), anionic surfactants can form a scum. To prevent this, chelating agents such as EDTA (ethylene diamine tetra-acetic acid), or amino carboxylic acids, are added. These sequester, or ‘lock up’, the calcium and magnesium ions so preventing scum formation.
The commonest disinfectants (sanitizers) are based on compounds that release chlorine such as hypochlorous acid (HOCl) or sodium hypochlorite (NaOCl). Chlorine has strong oxidizing properties that kill bacteria. Advantages are its effectiveness against most microbes, its cheapness and its being unaffected by hard water. A slight disadvantage of chlorine is that it is quite corrosive to metal. Quarternary ammonium compounds are much less corrosive but cannot be mixed with anionic detergents and are more expensive than chlorine-based disinfectants.
Neither are they as effective as chlorine against Gram-negative bacteria (see Chapter 9). They are, however, odour and taint free. A number of other types of disinfectant are available, often for specialist purposes.
Some cleansing systems are now based on foams. The foam sticks to surfaces and so increases the contact time, and therefore the effectiveness, of the system. Obviously, cleaners and disinfectants used in abattoirs must be non-toxic, must not lead to taints and should be as non-corrosive as possible. Also, after cleaning and disinfection it is important that all traces of the chemicals used are thoroughly rinsed away so no residues remain. It is important to clean plant and equip- ment throughout the daily operation as well as thoroughly at the end of the day. This can be done during, for example, refreshment and meal breaks so that normal operations are not disrupted.
By-products
In the early days of the meat packing industry in North America the offal, heads, guts and other parts removed from the dressed carcass were considered as waste products and thrown away. In Chicago in the early 1800s they were thrown into the local river until the smell became so bad that the city council forbade the practice. The material was then buried to dispose of it, or later, fed back to pigs. By the 1850s the value of the material previously considered waste was realized and plants would slaughter pigs for no charge except the right to keep the fat associated with the entrails and the bristles. Even now, the profit- ability of the slaughtering industry largely depends on the value of the by-products – the so-called ‘fifth quarter’ of the carcass.
By-products fall into four main categories. The most valuable are the edible by-products. These consist of livers, hearts, tongues, kidneys, spleens (melts), brains, blood, edible raw fat, pigs’ feet and cattle diaphragms (skirts) and various parts of the stomach and intestines.
The rumens and reticula of cattle, and sheeps’ rumens, produce edible tripe, the intestines of pigs, chitterlings, and the small intestines of cattle, sheep and pigs various types of sausage casings. In North America, offals such as liver, hearts, kidneys, tripe and tongues are referred to as ‘variety meats’. Gelatin is extracted from pig snouts and skin.
Cattle hides and pig skins go for the manufacture of leather. Sheep skins, known as pelts, are made into rugs, chamois leather and cloth- ing. Various organs and glands are used to produce pharmaceutical products. Heparin, used to prevent blood clotting, is extracted from lungs; insulin, for the treatment of diabetes, is extracted from the pancreases of pigs and cattle. Cattle pituitary, thymus and thyroid glands are also valuable in this regard. Rennet, used for curdling the milk in cheese making, is extracted from calves’ stomachs.
Edible bone, stomachs, lungs and spleens that are unsuitable for human consumption, are used for the manufacture of pet food, and blood, inedible fat and condemned carcasses and offal are processed into feed for livestock.
One of the most important factors determining the value of by- products is how well they are handled. Most are prone to rapid deterioration if not handled carefully and this leads to downgrading. A critical part of the handling is storage at low enough temperatures. Fats in particular are prone to oxidation and the development of rancidity.
Rendering
Waste tissues, including bones, meat and offal unfit for human or direct animal consumption, are disposed of by rendering. The material is cooked for an hour or longer with the aid of steam, sometimes under pressure, either in batch or continuous processes so that the fat melts and can be run off, and the remaining material breaks down. This produces tallow and, after the water has been boiled off, a residue known as greaves. The dried greaves are ground to produce meat and bone meal, which can be incorporated into animal feed as a protein source. The high temperature during cooking sterilizes the material.
The greaves will contain 10% or more fat. In some rendering processes they are further extracted with organic solvents. This increases the yield of tallow and reduces the fat content of the meat and bone meal. Hyperbaric rendering involves pressure-cooking the materials. Using pressures of 2–3 atm enables temperatures of between
120 and 130°C to be attained. The breakdown of the material is more effective and it is likely that all but the most resistant infective agents, such as those causing transmissable spongiform encephalopathies like BSE (Taylor et al., 1998), are destroyed.
Abattoir effluent
Very large quantities of water are used in the operation of slaughter plants. This is mainly used for cleaning and becomes very dirty with a high load of organic matter. This dirtiness is measured as its biological oxygen demand (BOD). The BOD is the amount of oxygen required to oxidize, and therefore break down, the organic matter completely in a certain time and at a certain temperature. Abattoir effluent may have a BOD five or six times that of normal domestic sewage and is therefore expensive to purify and has a high potential for polluting water- courses. Normally the effluent is given an initial cleaning treatment before it leaves the plant. Solids are screened out and fat particles removed by air flotation. Bacteria are then encouraged to break down remaining material, either anaerobically or aerobically, while it is held in tanks or ponds.
A period of time normally elapses between the slaughter of an animal and consumption of the meat. In practical terms, the carcass cools down and becomes stiffer or ‘sets’, the surface dries and the fat becomes firmer. With time, the texture and flavour of the lean improve.
These effects are accompanied by significant biochemical changes in the muscles: acidification, the development of rigor mortis and, later, the gradual resolution of rigor and tenderization of the meat by a process referred to as conditioning.