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Poultry slaughtering
Article index
 | Unloading bay | |
| Stunning | |
| Bleeding | |
| Scalding | |
| Plucking | |
| Neck slitting and foot removal | |
| Evisceration line | |
| Washing | |
| Chilling | |
| Draining | |
| Freezing |
Unloading bay
Legislation provides for the humane slaughter and pre-slaughter treatment of poultry (turkey, domestic fowl, guinea fowl or goose). On arrival of the transport vehicle into the covered slaughterhouse bay, living birds carried in fixed or loose plastic crates are unloaded and individually hung upside down by the feet on to the shackles from a continuously moving line. The centres of the shackles are approximately 15 cm apart. Ante-mortem inspection is carried out (crates are provided for birds rejected by the inspector).Stunning
The birds enter the slaughter room through a small narrow opening and are stunned instantaneously. Various types of electrical stunners are used. The birds are stunned either by their heads coming into contact with a 500 V electrified metal slope (wires) or by their heads passing through an electrically charged water bath with a variable voltage. The length of the water bath depends on the desired stunning time and line speed. Stunning with the normal mains frequency can result in bone fractures and in slight haemorrhages. That is why a high-frequency stunner is used with a frequency between 50 and 400 Hz.Recent research has shown that it is more humane to kill the birds in the stunner than just to stun them.
Bleeding
Within 30 seconds the birds are bled by an operator who severs either the right or left jugular vein at the base of the skull or automatically by a killer. Due to a precise way of positioning the head, the killer can apply a perfect slit at the side of the neck. Hereby the trachea and the gullet remain entirely intact. When the stunning has been effectively achieved, a consistent bleeding takes place.The birds now pass along a bleeding tunnel for at least 2 minutes for turkeys and at least 90 seconds for domestic fowls. This is to allow the birds to bleed before entering the scalding process. It is estimated that 50% of the blood is removed.
Scalding
The birds, still suspended from the line, pass through the scald tank in which there is continuously changing agitating water at a constant temperature between 50-80°C. Because of a controlled injection of air into the water through nozzles, a consistent, powerful turbulence is achieved which gives a better scalding effect.The time in the scald should be no more than 2 minutes. This ensures that the skin will be untorn and unblemished. The scalding loosens the feathers for the plucking process. Sometimes detergents are added to the scald water, making the penetration of the water to the feather follicles much easier.
Plucking
The birds pass into the plucking machines, which consist of revolving drums with rubber beaters or discs. The birds are continually flailed or scraped by these, while being sprayed with warm water. The process takes approximately 1 minute. Any feathers still remaining attached are removed by hand. Ducks are often further plucked by a hot wax process which removes the finer feathers and down.The first post-mortem inspection takes places in this area. Rejected birds are removed from the line.
To accelerate the removal of energy from muscles, electrical current pulses are applied to the carcass after plucking. The birds are then washed by overhead sprays.
Neck slitting and foot removal
A vertical incision is made in the skin on the dorsal surface of the neck to assist in the removal of the crop, oesophagus and trachea at a later stage. The feet are removed automatically by a cutter on the line or by manually operated scissors. The birds drop on to a conveyor that transfers them through a narrow opening from the “dirty” section of the slaughterhouse into the “clean” section.Evisceration line
The birds are hung up again by the hocks on to the shackles of the evisceration line. The line runs above a water trough or a mechanical conveyor, which carries away waste materials. Various operations are carried out on this line:• Head removal:
The heads are generally removed mechanically by traction of a head puller. After proper positioning the head and trachea puller breaks the spine at its weakest point after which the head, crop, oesophagus and trachea are stretched out.
• Venting:
Scissors cut a round vent in order to remove the intestines from the carcass. Great care is needed in this important operation as faecal contamination of the carcass, edible offals and operators’ hands has to be avoided.
• Drawing:
All of the viscera are drawn out of the body cavity, leaving them hanging from the carcass ready for inspection. The drawing is done either by hand or by operators using eviscerating forks or by automatic eviscerating machines.
At this point the inspectors examine the viscera, the body cavity and the carcass generally. Good lighting, properly directed into the body cavity is essential.
Some machines separate the viscera pack immediately from the carcass after drawing. The viscera packs can then be examined more quickly and under more hygienic conditions.
• Removal of offals:
The edible offals, i.e. the heart, liver and gizzard are removed for further cleaning and washing. The intestines, proventriculus and lungs are discarded into the water trough or mechanical conveyor. On some lines a suction tube is then introduced into the body cavity to remove any contamination or portions of lungs remaining.
When the viscera pack is already separated automatically, all operations on the pack can also be carried automatically. This results in a higher heart and liver yield and better microbiological quality.
An inspector or a quality control officer then examines the carcass generally, especially the body cavity.
• Neck removal:
The necks are removed by cutting through the vertebrae between the shoulders using automatic or manual scissors. The necks are classified as part of the edible offal or giblets.
• Line washing:
Before going into the washing and cooling tanks the birds are spray washed to remove blood and extraneous matter.
• Polyphosphate injection:
When polyphosphates are used, they are injected under pressure by guns with two hollow perforated needles. The solution is injected into the breast and sometimes also into the leg muscles. Up to 5% of the body weight of this permitted additive solution may be injected.
Washing
The carcasses can be dropped automatically from the evisceration line into long spin washer tanks, which contains water at a temperature of 10-16°C. The birds have a body temperature of 36°C. After 10 minutes in the washer the carcasses are about 24°C. The carcasses are propelled along the tanks by revolving rubber paddles. The water through the tanks may be with or contra-flow the direction of the carcasses. Chlorination is used at a level of 50 ppm free chlorine, which kills almost completely all bacteria in the tanks.Chilling
The carcasses are transferred from the washer unit by an elevator into the long immersion chiller tank. This works on the same principle as the washer unit. Flake ice is dropped into the water in the chiller tank from overhead flake-ice machines. Some chillers are fed with refrigerated water. The birds remain in the chiller tank for 30-40 minutes and leave at a temperature of 2-4°C.Chilling can also be achieved by accurately directed flow of cold air or by water film chilling, based on the evaporation of moisture which remove the heat from the carcass.
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