Dressing Techniques for Pigs: From Scalding to Evisceration

Pig dressing stands apart from the processing of almost every other livestock species because of one fundamental difference: the skin stays on. While cattle are dehided and sheep are fleeced, pigs retain their skin throughout the entire dressing process. This makes pig processing a uniquely specialized operation, demanding a distinct sequence of steps – scalding, dehairing, singeing, evisceration, washing, and postmortem inspection – each of which directly impacts the safety, hygiene, and quality of the final pork product.

Why pig dressing is different from other livestock 🔗

In cattle and sheep dressing, removing the hide or fleece is one of the earliest and most critical steps. Pig dressing takes a completely different path. The pig’s skin is retained because it holds culinary and commercial value – it is used in crackling, sausage casings, and gelatin production. However, keeping the skin means the hair must be removed through physical and thermal treatment, rather than simply pulling off a hide. This requires a sequence of operations – scalding, dehairing, and singeing – that are virtually exclusive to pig processing.

Before any of this begins, the pig undergoes stunning and bleeding (exsanguination). After stunning, the animal is shackled by the hind leg and hoisted on a rail. The jugular vein is severed with a sticking knife to initiate rapid bleeding. The sticking cut must be precise – for pigs, the knife is inserted just above the breastbone, directed toward the head, ensuring the carotid arteries and jugular veins are severed cleanly. Care must be taken not to puncture the chest cavity, which could allow blood to pool internally and compromise the carcass. The sticking wound should also be kept small to reduce contamination when the pig enters the scalding tank.

Scalding: the first major step after bleeding 🔗

Once bleeding is complete, the carcass moves to scalding – the process that makes hair removal possible. Scalding is accomplished by submerging the entire carcass in hot water, typically at 60-63°C, for several minutes. The heat penetrates the hair follicles and weakens the keratin proteins that anchor each hair to the skin, loosening the grip without cooking the skin itself.

Temperature control is everything at this stage. Using a water temperature of 58-62°C, the scalding process requires 4-6 minutes. If the temperature is too high – above 62°C – it causes coagulation of the skin proteins, which actually makes hair harder to remove and can damage the skin surface. If it’s too low, the follicles don’t loosen sufficiently, and manual labor increases significantly.

There are two primary scalding methods used in abattoirs today. Vat scalding involves immersing the carcass in a tank of hot water. A disadvantage of vat scalding is the possibility that scalding water can enter the lungs and, via the sticking wound, into deeper tissues of the carcass, introducing bacteria. Because multiple carcasses are processed in the same water, this method carries a bacteriological risk, making it critical that the water temperature be maintained above 60°C to limit microbial load. The alternative – the scalding tunnel – conveys pigs on a hanging rail through a chamber where they are sprayed with hot water or exposed to steam. This method is more hygienic, reduces cross-contamination between animals, and is preferred in larger, modern facilities.

Dehairing: removing the loosened hair 🔗

Dehairing must begin promptly after scalding. If the carcass cools, the follicles begin to tighten again, making hair removal more difficult. Dehairing is done with a specially formed scraper (bell scraper or knife), and if the scald is effective, all the hair can be removed by this manual method.

Mechanical dehairing 🔗

In modern commercial abattoirs, mechanical dehairing machines handle most of the work. Dehairing machines are constructed from heavy U-shaped bars, a steel frame, and one or two shafts to which belt scrapers are attached. The hogs are sprayed with water as they pass lying and rotating through the dehairer. The rotating rubber paddles or scrapers flex against the skin surface, dislodging the loosened hair without tearing the underlying tissue. Water sprays simultaneously flush away removed hair and keep the carcass surface clean throughout the process.

Some facilities use a combined scalding and dehairing tank in a single operation. Inside the tank are rotating rubber-tipped paddles which are started after closing the lid. As the hair is loosened by the scalding water it is removed by the rubbing effect of the paddles against the skin. This is particularly common in smaller operations where space and capital investment are limited.

Manual dehairing 🔗

In smaller abattoirs, manual dehairing remains common. Workers use bell scrapers – curved, blunt metal tools – to scrape hair from the carcass surface systematically. The scraping must follow the direction of the hair follicles to be effective. According to standard meat technology practice, a blunt knife is used during manual dehairing to avoid cutting the skin while dislodging bristles. This method is more labor-intensive but allows for more precise control, especially in areas where hair tends to be more stubborn, such as the head, ears, and feet.

An alternative used in some facilities involves dipping the pig in a bath containing a hot resin adhesive. The pig is removed from the bath and the resin allowed to set partially, when it is peeled off pulling the hair with it from the root. This method is less labor-intensive than scraping and produces a clean skin finish. The resin can be melted, strained of hair, and reused, making it cost-effective in certain operations.

Singeing: burning away what scrapers miss 🔗

Even after thorough scalding and dehairing, fine residual hairs and stubble remain embedded in the skin – particularly in skin folds, around the ears, and near the feet. Singeing addresses this. Singeing removes any remaining hairs, shrinks and sets the skin, decreases the number of adhering micro-organisms, and leaves an attractive clean appearance. It may be done with a hand-held gas torch.

In larger facilities, automated systems transport the pig into a furnace and leave it long enough for an effective singe. The temperature inside a singeing chamber can reach extremely high levels. The temperature of a singeing chamber can be about 1200°C, and the surface of the carcass can rise to over 100°C after only a 10- to 15-second exposure. This brief but intense heat burns residual hair completely while also reducing surface bacteria – an important food safety benefit.

After singeing, the blackened deposits and ash must be removed. After singeing, black deposits and singed hairs are scraped off, and the carcass is thoroughly cleaned before evisceration begins. The carcass then receives a rinse with clean, potable water to cool the skin, remove residue, and prepare it for the next stage.

Evisceration: removing the internal organs 🔗

With the exterior of the carcass now clean and hair-free, attention shifts to the body cavity. Evisceration in pigs follows principles similar to cattle processing, with some adaptations for the pig’s anatomy. When a carcass is to be dressed with the skin left on, the skin shall be thoroughly washed and cleaned before any incision is made for the purpose of evisceration.

The process starts with a circumanal incision – a circular cut around the anus using a sharp knife to free the terminal end of the large intestine from its attachments. The distal end of the rectum is then tied off, typically with a rubber band or ligature, to prevent any intestinal contents from contaminating the carcass during subsequent steps. This is a critical hygiene control point. Data indicate that carcasses were contaminated with bacteria mainly during dehairing and operations on the head, making proper technique at each step essential.

Next, a midventral incision is made from the midpoint of the pubic symphysis up to the level of the sternum. A longitudinal incision is made from the pubis to the neck to remove the offal. This opening must be controlled and precise – any accidental puncture of the stomach, intestines, or bladder can release contents that contaminate the meat surfaces with bacteria and render sections of the carcass unfit for consumption.

Systematic organ removal 🔗

Once the abdominal cavity is open, the omental and mesenteric fats are first cleared away to expose the organs. The digestive organs – stomach and intestines – are removed first, followed by the reproductive organs and urinary bladder. After dehairing or skinning, the abdominal and thoracic cavities are opened and the internal organs removed. Certain organs are washed, inspected, and saved as edible byproducts.

The thoracic cavity is then opened by continuing the midventral incision through the sternum, often using a saw or cleaver. The heart and lungs are typically removed together as a unit along with the trachea and esophagus – this combined structure is commonly referred to as the “pluck.” The liver is removed intact, with care taken not to puncture the gallbladder, as bile spillage can taint surrounding tissue. Throughout the entire evisceration, workers regularly sterilize their knives in hot water (82°C) to prevent cross-contamination between carcasses.

Carcass washing and preparation for inspection 🔗

After evisceration, the carcass is washed thoroughly with clean, potable water. High-pressure sprays or hoses are used to clean all internal and external surfaces, flushing away blood, bone fragments, and any debris that may have accumulated during dressing. Carcasses should be washed by spraying potable water on the surface and on the thoracic and abdominal cavity. This step is not merely cosmetic – it is a direct food safety measure that reduces surface bacterial loads before the carcass enters cold storage or inspection.

The removed organs are kept alongside the carcass and not separated from it at this stage. This is important for the next step: postmortem inspection must correlate the carcass with its organs for a complete evaluation.

Postmortem examination: the final safety check 🔗

The dressed carcass and all associated offal are presented together for postmortem inspection by a qualified veterinarian or official inspector. This inspection is a legal and public health requirement in virtually all regulated meat production systems. Inspectors examine animals immediately after slaughter and evisceration for possible changes and lesions that indicate unsuitability of the meat for food. Postmortem examination requires observation of all parts of the carcass, dressing procedures, equipment, and facilities to prevent contamination of edible parts.

For pigs specifically, the inspection covers the head, viscera, and the full carcass. Lymph nodes are incised and examined, organ surfaces are visually assessed and palpated, and the overall condition of the carcass is evaluated for any sign of disease, parasites, or systemic infection. Conditions such as pneumonia, pleuritis, liver lesions, and pericarditis are among the most commonly detected findings at postmortem. Research from pig slaughterhouses shows that pleuritis, pneumonia, liver alterations, and pericarditis are the most frequent lesions detected after slaughter.

The outcome of inspection results in one of three dispositions: passed (fit for human consumption and eligible for the mark of inspection), retained (held for further veterinary review), or condemned (deemed unfit and removed from the food chain). On-line post-mortem inspection activities include inspecting the head, viscera, and carcass of each animal at fixed locations on the evisceration line. Only carcasses that pass this final evaluation are cleared for chilling, further processing, or retail distribution.

The entire pig dressing sequence – from the sticking knife to the inspector’s stamp – is not simply a processing routine. It is a tightly controlled chain of hygiene, precision, and food safety measures, each step building on the last. The retention of the skin may seem like a minor biological detail, but it fundamentally shapes every decision made in the dressing process, from the temperature of the scalding tank to the flame intensity of the singeing torch.

What do you think? Given that vat scalding carries a documented risk of bacterial contamination inside the carcass, should smaller abattoirs be required to invest in scalding tunnels regardless of cost? And at what point in the dressing process do you think the greatest contamination risk occurs – during dehairing, evisceration, or somewhere else entirely?

References

1. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/pig-slaughter
2. https://www.fao.org/4/t0279e/t0279e04.htm
3. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dehairing
4. http://meattechnologyblog.blogspot.com/2014/01/dressing-of-animals.html
5. https://www.fao.org/4/y5454e/y5454e09.pdf
6. https://www.ecfr.gov/current/title-9/chapter-III/subchapter-A/part-310
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC340019/
8. https://www.cfs.gov.hk/english/import/import_smi.html
9. https://www.msdvetmanual.com/clinical-pathology-and-procedures/meat-inspection/postmortem-inspection-of-production-animals
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC10044242/
11. https://www.fsis.usda.gov/policy/fsis-directives/6600.1