Food Science & Technology · Commodity Processing Technologies · also Meat Technology, Processed Meat Products, Poultry and Egg Technology, Livestock Products Technology
Processed meat, poultry and egg products: meat as a raw material, curing and smoking chemistry, emulsion and restructured products, canned and dried meats, poultry further processing, and egg quality and egg products. Slaughter, inspection and abattoir design are in the Veterinary track (meat-science-abattoir, milk-meat-hygiene-food-safety).
In the exams: GATE XE-G Section 1 (post-mortem changes) and Section 3 (canning, drying and freezing of meat; egg powder); ICAR AIEEA-PG Code 18 Unit III; ICAR AICE 35.a Unit 3
Meat, poultry and eggs are among the most nutritious and the most perishable foods people eat. Muscle and egg are rich in high-quality protein, water and minerals, which makes them excellent media for microorganisms and gives them chemistry, such as the pigment myoglobin and the delicate proteins of egg white, that changes visibly with every step of handling. Meat and egg technology is the science of turning these raw materials into safe, consistent products: cured hams and bacon, sausages, nuggets and formed products, canned and dried meats, further-processed poultry, and liquid, frozen and dried egg.
This manual starts from the muscle and the egg as raw materials. It explains how muscle becomes meat after slaughter, why some carcasses give pale, watery pork or dark, sticky beef, and how tenderness can be improved. It then covers the chemistry of curing and smoking, the physics of meat batters and binding, preservation by heat, drying and cold, poultry further processing, and egg quality and egg products. Slaughter, stunning, carcass dressing, ante-mortem and post-mortem inspection and abattoir design belong to the Veterinary track (meat-science-abattoir and milk-meat-hygiene-food-safety); freezing equipment and freezing-time calculation are in chilling-freezing-frozen-foods; thermal process lethality is in thermal-processing-canning; and fish smoking and fish products are in fish-seafood-processing. Those subjects are referred to here, not repeated.
The subject is examined in GATE XE-G Section 1 (post-mortem changes in meat) and Section 3 (canning, drying and freezing of meat; egg powder), ICAR AIEEA-PG Code 18 Unit III and ICAR AICE 35.a Unit 3, and it is the daily work of technologists in meat plants, poultry processors and egg-breaking plants worldwide. Permitted additives, especially nitrite and phosphates, and product definitions differ between countries, so a practitioner must always read the current regulation of the market.
Skeletal muscle, the raw material of most meat, is built in a hierarchy. The whole muscle is wrapped in a connective tissue sheath, the epimysium. Inside, bundles of fibres (fascicles) are wrapped in perimysium, and each fibre, a single long multinucleate cell, is surrounded by endomysium. These connective tissue layers, mainly collagen with some elastin, carry blood vessels and nerves, transmit force to the tendons, and contribute the background toughness of meat. Each fibre is packed with myofibrils, and each myofibril is a chain of repeating contractile units, the sarcomeres. Under the microscope the sarcomere shows dark A bands, where thick myosin filaments lie, and light I bands of thin actin filaments, bounded by Z lines. Contraction is the sliding of actin over myosin, which shortens the sarcomere; the length of the sarcomere at the time meat sets in rigor has a strong effect on tenderness.
Muscles differ in fibre type. Red (slow, oxidative) fibres are rich in myoglobin and mitochondria and are used for sustained activity; white (fast, glycolytic) fibres have less myoglobin and more glycogen. This is why poultry leg meat is darker than breast meat, and why muscles used for locomotion and posture are darker and often tougher than little-used muscles.
Lean muscle is roughly three-quarters water, about a fifth protein, a few per cent fat within the muscle (intramuscular fat or marbling), about 1% carbohydrate, mostly glycogen, and about 1% minerals. These figures vary with species, breed, age, muscle and nutrition, and with the amount of fat trimmed. Muscle proteins fall into three groups. Myofibrillar proteins, about half of the total, include myosin and actin, which form actomyosin, together with the regulatory proteins tropomyosin and troponin; they are soluble in salt solutions and are responsible for the water-holding, binding and emulsifying properties of meat in processing. Sarcoplasmic proteins, about a third, are the water-soluble proteins of the cell fluid, including the glycolytic enzymes and myoglobin, the pigment that gives meat its colour. Stromal proteins, chiefly collagen and elastin, are the connective tissue proteins; they are insoluble and their amount and cross-linking set the background toughness of a cut.
Collagen becomes more heat-stable and less soluble as the animal ages, because its cross-links mature; this is why meat from older animals is tougher and needs long, moist cooking that converts collagen to gelatin. Meat is also an important source of iron in the haem form, which is better absorbed than plant iron, of zinc and of vitamin B12.
Fat is deposited in several places: subcutaneous fat under the skin, intermuscular fat between muscles, intramuscular fat within the muscle, and internal fats around organs. Its quantity and composition affect yield, flavour, juiciness, texture and keeping quality. The fatty acid composition depends on species and diet. Ruminant fats are relatively saturated and firm because rumen microorganisms hydrogenate dietary unsaturated fatty acids. Pig and poultry fats reflect the diet more closely; a diet high in unsaturated oils gives soft, oily fat that is difficult to slice and oxidises more readily. Oxidation of unsaturated fatty acids, especially in phospholipids of cell membranes, gives rancid and warmed-over flavours in stored, cooked and frozen meat, and is accelerated by haem iron, salt and grinding. Antioxidants, both from the animal's diet (vitamin E) and added in processing, slow these changes. Fat content is the main source of variation in the energy value of meat and must be declared accurately on processed products.
When the blood supply stops at slaughter, muscle loses its supply of oxygen but continues to need energy. It keeps making ATP anaerobically by breaking down glycogen to lactic acid, and because the lactic acid can no longer be removed by the blood, it accumulates and the pH falls. In a normal carcass the pH falls from about 7.0–7.2 in living muscle to an ultimate pH commonly around 5.4–5.8, often near 5.5. The rate and extent of this fall depend on the glycogen reserve at slaughter, the temperature of the carcass, the species and the muscle. If glycogen has been depleted by stress, exercise or fasting before slaughter, less lactic acid forms and the ultimate pH stays high. If glycolysis is very rapid while the carcass is still hot, the pH falls too fast. Both departures cause quality defects, described in the next chapter. The ultimate pH is one of the most important measurements in meat science because it predicts colour, water-holding capacity, tenderness and keeping quality.
As ATP is used up, myosin heads bind permanently to actin, forming actomyosin, and the muscle becomes stiff and inextensible: this is rigor mortis. Before rigor the muscle is soft and extensible; at full rigor it is rigid; with time it softens again as ageing proceeds. The time to the onset of rigor depends on species and temperature; it is generally shorter in poultry and pigs than in cattle and sheep.
Temperature during the pre-rigor period matters greatly. If carcass muscle of beef or lamb is chilled below about 10–15 °C while the pH is still high and ATP is present, the muscle contracts strongly, a phenomenon called cold shortening, because the sarcoplasmic reticulum releases calcium in the cold and the mitochondria cannot take it up. The sarcomeres shorten and the meat becomes very tough. Very rapid freezing of pre-rigor meat followed by thawing causes an even more severe contraction, thaw rigor, with large drip loss. Cold shortening is avoided by holding carcasses at moderate temperature until the pH has fallen, by hanging carcasses from the pelvis (tenderstretch) so that key muscles are held stretched, or by electrical stimulation, which accelerates glycolysis so the muscle enters rigor before it becomes cold.
After rigor, meat held under refrigeration becomes more tender over days to weeks. This ageing or conditioning is mainly the work of the muscle's own proteolytic enzymes. The calpains, calcium-activated proteases, degrade key myofibrillar and cytoskeletal proteins such as desmin and titin, weakening the structure at and around the Z lines; their activity is regulated by the inhibitor calpastatin, whose level varies between species and breeds and helps explain why some cattle give less tender meat. Cathepsins, lysosomal proteases, also contribute. Ageing proceeds faster at higher temperature but so does microbial growth, so beef is commonly aged at about 0–4 °C. Most of the improvement in beef occurs in the first one to two weeks; pork and poultry age faster.
Wet ageing is done in vacuum packs and gives little weight loss. Dry ageing hangs carcasses or primals uncovered in controlled cold, humid, ventilated rooms; it gives a concentrated, characteristic flavour but loses weight by evaporation and trimming of the dried surface. Ageing also develops flavour precursors from protein and nucleotide breakdown.
The colour of fresh meat depends on the concentration of myoglobin and its chemical state. Myoglobin content rises with species (beef is darker than pork, which is darker than chicken breast), with age and with muscle activity. Its colour depends on the state of the iron in the haem group and on what is bound to it. Deoxymyoglobin, with ferrous iron and nothing bound, is purplish red; it is the colour of the interior of fresh meat and of vacuum-packed meat. When exposed to air, oxygen binds to it to form oxymyoglobin, which is bright cherry red, the bloom that consumers associate with freshness. When the iron is oxidised to the ferric state, metmyoglobin forms, which is brown; it appears at low oxygen pressure, with time, with surface drying, and with microbial growth, and the meat is judged stale even if it is safe.
Packaging is designed around these states. Air-permeable overwrap gives bright red for a few days. Vacuum packs keep purple deoxymyoglobin and long life, and the meat blooms when opened. High-oxygen modified atmosphere packs extend the red bloom but accelerate lipid oxidation, while low-oxygen packs with carbon monoxide, permitted in some countries and not in others, stabilise a red colour. Cured meat colours are formed by nitric oxide and are discussed in the curing chapter.
Water-holding capacity (WHC) is the ability of meat to keep its own water during cutting, heating, grinding and storage. Most water in muscle is held in the spaces between the myofibrillar filaments and between the fibres. Water-holding is lowest near the isoelectric point of the main myofibrillar proteins, around pH 5.0–5.2, where the proteins carry little net charge, pull together and leave less room for water. Raising the pH away from this point, or adding salt, which increases electrostatic repulsion and dissolves myofibrillar protein, increases WHC; this is why salt and phosphates are used in processed meats. Pre-rigor meat has high WHC because ATP keeps the filaments apart, which is why hot-boned, pre-rigor meat makes good sausages if it is salted quickly.
Poor WHC shows as drip in packs, weight loss in storage, cooking loss and dry eating quality, and it costs the processor yield. Drip loss is measured as the percentage of weight lost when a sample is hung or stored for a set time: a 500 g sample that weighs 470 g after storage has lost 30 g, a drip loss of 6.0%.
Two defects show how the rate and extent of pH fall control quality. Pale, soft, exudative (PSE) meat occurs mainly in pork and in poultry breast. When glycolysis is very rapid, the pH falls low while the carcass is still hot; the combination of low pH and high temperature denatures myofibrillar and sarcoplasmic proteins, which lose water-holding capacity, scatter more light and look pale, and the meat is soft and loses much drip. In pigs, PSE is strongly associated with a mutation in the ryanodine receptor gene (the halothane gene) that makes the animals stress-susceptible, and with acute stress just before slaughter. It is commonly identified by a low pH measured within about an hour after slaughter. PSE pork gives poor yields in cured and cooked products.
Dark, firm, dry (DFD) meat, called dark cutting in beef, is the opposite. When glycogen has been depleted before slaughter by prolonged stress, fatigue, fighting, transport or fasting, little lactic acid forms and the ultimate pH stays high, commonly above about 6.0. The proteins hold water tightly, the surface looks dark and dry, the meat is firm and sticky, and because the high pH favours bacterial growth, it spoils faster. Good handling of animals before slaughter, breeding and rest periods reduce both defects.
Tenderness has two main components. The background toughness comes from connective tissue, its amount and the maturity of its collagen cross-links, and it differs between cuts and rises with age. The myofibrillar component comes from the state of the contractile apparatus: how short the sarcomeres were when rigor set in, and how far the myofibrillar structure has been degraded by ageing. Cooking adds its own effect: heating to moderate temperatures shrinks collagen and toughens myofibrils, while long, moist cooking at lower temperatures converts collagen to gelatin and tenderises connective-tissue-rich cuts. Tenderness is measured instrumentally by the Warner–Bratzler shear force of a cooked core, or by slice shear force, and by trained or consumer sensory panels.
Pre-slaughter and post-slaughter controls on tenderness include the age and breed of the animal, avoiding cold shortening by suitable chilling or electrical stimulation, carcass suspension, and adequate ageing, all covered in earlier chapters. This chapter covers interventions on the meat itself.
Mechanical methods break fibres and connective tissue physically. Blade or needle tenderising passes rows of thin blades or needles through whole cuts, cutting fibres and connective tissue while keeping the cut intact. Cubing and scoring cut the surface, and grinding reduces meat to small particles, removing the structure altogether. Massaging and tumbling in rotating drums, often under vacuum and with brine, flex and abrade the meat, extract salt-soluble proteins to the surface, and improve tenderness and brine uptake; they are standard in ham and poultry processing.
Mechanical tenderising and injection carry a safety consequence. The surface of an intact cut may carry pathogens such as Escherichia coli O157:H7, but the interior is normally sterile, so a rare-cooked steak is low risk. Blades and needles can carry surface organisms into the interior, where rare cooking will not destroy them. Several countries therefore require mechanically tenderised beef to be labelled with cooking advice, and processors sanitise blades and control the microbial load of the surface before tenderising.
Plant proteases are used to tenderise meat by digesting connective tissue and myofibrillar proteins. Papain from papaya latex, bromelain from pineapple stem, ficin from fig latex and actinidin from kiwifruit are the main ones; papain and bromelain act strongly on collagen and elastin. They are applied as powders or marinades on the surface, injected, or in some countries given to the animal before slaughter. Their main limitation is control: surface application gives uneven tenderising, enzymes act most rapidly during cooking until heat inactivates them, and over-tenderised meat becomes mushy with poor texture. Microbial proteases are also used.
Other approaches include injection of calcium chloride solution, which activates the calpains and speeds ageing; marinating in acids such as vinegar, wine or fruit juice, which swells and partly solubilises connective tissue and raises water uptake (the pH moves away from the isoelectric point); high-pressure processing of pre-rigor meat; and shock-wave treatment, still experimental. The choice depends on the product, cost, labelling rules and the consumer's acceptance of the texture produced.
Curing is the treatment of meat with salt and nitrite (or nitrate), usually with sugar, phosphates and a cure accelerator such as ascorbate or erythorbate, to give characteristic colour, flavour, texture and keeping quality. Salt lowers water activity, extracts myofibrillar proteins and contributes flavour. Sugar balances the saltiness and, in fermented products, feeds lactic acid bacteria. Phosphates raise pH and ionic strength and improve water-holding and yield. Ascorbate and erythorbate speed the reduction of nitrite to nitric oxide, stabilise cured colour and reduce nitrosamine formation.
Cure is applied in several ways. Dry curing rubs the salt mixture onto the surface and lets it diffuse in over days to weeks, as for traditional hams and bacon. Pickle or brine curing immerses meat in a curing brine. Injection (stitch or multi-needle pumping) puts brine directly into the meat, followed by tumbling for distribution; this is fast and standard in modern ham and bacon plants. The level of each ingredient in the finished product depends on the brine strength and the amount injected, called the pump or injection level. If 100 kg of pork is injected to 110 kg with a brine containing 20% salt, the meat has taken up 10 kg of brine and 2 kg of salt, giving 2 ÷ 110 = 1.82% salt in the product before any cooking loss. Ingoing and residual nitrite limits are set by each country's regulation.
Nitrite in meat forms nitric oxide, a process helped by the reducing conditions of muscle and by ascorbate. Nitric oxide binds to the iron of myoglobin to form nitrosylmyoglobin, which is red; on heating, the globin protein denatures and the pigment becomes nitrosyl haemochrome (nitrosylhaemochromogen), the stable pink colour of cooked cured meats such as ham and frankfurters. Cured colour fades when exposed to light and oxygen, because nitrosyl haemochrome is oxidised, which is why cured meats are packed in vacuum or modified atmosphere and protected from light in display.
Nitrate, used in traditional cures, has no direct effect; it must first be reduced to nitrite by nitrate-reducing bacteria such as micrococci and staphylococci, which is why nitrate is slower and is now used mainly in slow, traditional dry-cured products. Too little nitrite gives grey or brown areas; uneven distribution gives patchy colour. Green discoloration can arise from excess nitrite (nitrite burn) or from bacterial production of hydrogen peroxide or hydrogen sulphide reacting with the pigment.
Nitrite has three technical roles besides colour. It gives the characteristic cured flavour; it acts as an antioxidant, preventing warmed-over flavour; and, most importantly, it inhibits the outgrowth of Clostridium botulinum spores and the formation of botulinum toxin in cured products, especially in shelf-stable and vacuum-packed products, acting together with salt, pH and heat treatment. This anti-botulinal effect is the main reason regulators continue to permit nitrite despite concerns.
The concern is nitrosamines. Nitrite can react with secondary amines to form N-nitrosamines, many of which are carcinogenic in animals. Formation is favoured by high temperatures, as in frying bacon crisply, and by high residual nitrite. Ascorbate or erythorbate reduce nitrosamine formation by speeding the conversion of nitrite to nitric oxide, and limits on ingoing nitrite in bacon are often lower than in other products. Natural or vegetable-derived cures use nitrate from vegetable powders such as celery with a starter culture to form nitrite; they are still nitrite cures in chemical terms, and labelling rules for them differ between countries.
Smoke is produced by the slow, incomplete combustion (pyrolysis) of wood, usually hardwood such as oak, beech, hickory or fruit woods, as sawdust or chips. The wood's cellulose, hemicellulose and lignin break down into hundreds of compounds carried in the vapour and particle phases. The most important groups are phenols, mainly from lignin, which give smoky flavour and act as antioxidants and antimicrobials; carbonyl compounds, which react with amino groups at the meat surface by Maillard-type reactions and give the brown smoked colour; and organic acids, which help coagulate surface proteins to form a skin, aiding peeling of skinless sausages. Smoke also deposits polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene, which are carcinogenic; they form mainly at high combustion temperatures.
Smoking preserves partly by surface drying, by antimicrobial phenols and acids, and, in hot smoking, by cooking; but in most modern products smoking contributes flavour and colour more than preservation, and the product relies on salt, chilling and packaging. The chemistry of smoked fish, cold-smoked salmon and fish drying is covered in fish-seafood-processing.
Cold smoking is done at low temperatures, commonly below about 30 °C, so the product is flavoured and partly dried but not cooked; it is used for some fish, dry sausages and raw hams, which must be safe through salting, drying or fermentation. Hot smoking raises the product to cooking temperature in the smokehouse, giving a cooked, smoked product such as frankfurters, smoked chicken and hot-smoked fish. Modern smokehouses control air temperature, humidity and velocity through programmed cycles of drying, smoking, cooking and showering.
Smoke deposition is favoured by a moist but not wet surface, adequate smoke density and air movement. Smoke generators control combustion temperature to limit PAH formation; smoke can be cleaned by filtering, washing or electrostatic precipitation. Liquid smoke, made by condensing wood smoke in water and refining it to remove much of the tar and PAH, is applied by atomising, drenching or adding to the product; it gives more consistent results, less pollution and lower PAH levels. Smoke flavourings are regulated as flavourings in many jurisdictions, with specific approval of individual primary products in some, such as the European Union.
Comminuted meat products are made from meat reduced in particle size, from coarse ground sausages to finely chopped frankfurters, bologna and luncheon meats. In finely comminuted products, lean meat, fat, ice or water, salt, phosphates and seasonings are chopped in a bowl chopper (bowl cutter) or emulsion mill into a meat batter, often called a meat emulsion. Salt, with phosphates, extracts the myofibrillar proteins, mainly myosin, from the disrupted muscle. These dissolved proteins form a film around the small fat particles and bind water; on heating they gel, forming a network that traps fat and water and gives the cooked product its texture. The batter is therefore better described as a fat dispersion stabilised by a protein matrix than as a true emulsion.
Temperature during chopping is critical. Mechanical energy heats the batter; ice is added to keep it cold. If the batter becomes too warm, commonly above about 12–15 °C for pork and beef batters (the safe end-point temperature depends on the fat used), the fat softens and melts, the protein film cannot hold it, and the cooked product shows fat separation (fatting out), jelly pockets and poor texture. Over-chopping has the same result. Batter stability is tested by cooking samples and measuring fat and water released.
Sausage formulation balances lean, fat, water, protein and cost. Lean meats with high salt-soluble protein and good binding (bull meat, lean beef, pork trimmings) are distinguished from fillers with poor binding (high-collagen meats, heart, tripe). Non-meat binders and extenders include soy and milk proteins, starches and fibres, whose use and labelling are regulated. Water added during processing is controlled in some countries by rules based on the natural ratio of water to protein in lean meat. Under the Feder approach used in the United States, the water expected from the meat is about four times its protein content, so added water is estimated as moisture − 4 × protein: a frankfurter with 55% moisture and 12.5% protein has 55 − 50 = 5% added water by this rule. Fat content is also limited for many named products.
Casings shape the product and control its appearance. Natural casings are cleaned intestines of pigs, sheep and cattle; manufactured casings include collagen casings (edible), cellulose casings (peeled off after cooking for skinless frankfurters) and plastic casings (impermeable, for cooked products such as bologna and liver sausage). Co-extrusion forms a collagen or alginate casing around the batter as it is extruded.
Sausages fall into three broad technological groups. Fresh sausages are raw, seasoned ground meat sold refrigerated or frozen and cooked by the consumer. Cooked sausages, such as frankfurters, bologna and liver sausage, are filled, often smoked, cooked to a safe internal temperature, chilled and packed. Fermented sausages, such as salami and pepperoni, are made from raw meat and fat with salt, nitrite or nitrate, sugar and spices, inoculated with starter cultures of lactic acid bacteria (Lactobacillus and Pediococcus species) and often nitrate-reducing staphylococci; fermentation lowers the pH, commonly to about 5.3 or below, and drying then lowers water activity, so that the product becomes stable without cooking. The combination of nitrite, low pH and low water activity forms a hurdle system that controls pathogens; Escherichia coli O157:H7 and Listeria monocytogenes outbreaks linked to fermented sausages showed that the hurdles must be validated. Semi-dry sausages are fermented to a low pH and often cooked; dry sausages are dried for weeks to low water activity. Mould-ripened sausages carry selected moulds on the surface.
Restructured meat products are made by reducing meat to pieces, chunks, flakes or coarse particles and binding them back together into a product of uniform shape, size and composition: formed steaks and roasts, nuggets, patties, rolls, formed hams and doner-style cones. Restructuring adds value to lower-value trimmings, gives portion control and uniform cooking, and allows composition to be adjusted. The first step is particle reduction by grinding, flaking, dicing or slicing; the size of the particles decides whether the product resembles whole muscle or a ground product. The pieces are then bound and formed by moulding, stuffing into casings or forming machines, and are often frozen or cooked to set their shape. The raw material is selected and trimmed to a target lean-to-fat ratio, because fat content controls juiciness, cost and cooking loss, and connective tissue and bone fragments are removed or reduced, often by automated detection systems. Temperature is kept low throughout, commonly just above freezing, both to slow microbial growth on the large cut surfaces and to make the meat firm enough to form cleanly. Tempered frozen meat, just below its freezing point, is often used for slicing and flaking because it cuts into regular pieces.
Binding is the key technical problem. The classic system relies on salt and phosphate: massaging or tumbling the pieces with salt and phosphate extracts myofibrillar protein to the surface as a sticky exudate, which gels on heating and glues the pieces together. This works well for cooked products but gives no bind in raw products and adds sodium.
Cold-set binders were developed to bind raw products. Alginate with a calcium source forms calcium alginate gels at refrigeration temperature. Microbial transglutaminase catalyses cross-links between glutamine and lysine residues of proteins and binds pieces of meat, fish or poultry without heat. Fibrinogen and thrombin from animal blood plasma form a fibrin clot that binds pieces, as in blood clotting; its use is permitted in some countries and not in others. Non-meat proteins such as soy isolate, milk proteins and egg white, and starches and gums improve binding, water retention and slicing. Because restructured products can look like whole-muscle cuts, labelling regulations in many countries require the binding agent and the formed nature of the product to be declared, so that consumers are not misled and so that they cook the product thoroughly, because surface contamination is distributed through it.
Many restructured products are coated: predust (dry flour or starch to help adhesion), batter (a liquid mixture of flour, starch, water and seasoning) and breading (crumb). The coated product is often flash-fried or par-fried to set the coating and then frozen; the consumer finishes cooking. Coating pick-up, the proportion of coating in the final product, affects cost, appearance and fat uptake and is monitored by weighing.
Quality problems include poor bind, causing products to fall apart on slicing or cooking; excessive cooking loss; rancidity, because grinding and salt accelerate lipid oxidation; colour loss; and, in coated products, coating loss or blistering. Safety is managed by the same principles as for ground meat: because pathogens on the surface of the original pieces are mixed through the product, restructured and ground products must be cooked to a safe core temperature, and processors validate cooking steps for ready-to-eat items and control Listeria after cooking.
Meat is a low-acid food, with a pH well above 4.6, so canned meat must receive a sterilising process in a retort that destroys Clostridium botulinum spores, the botulinum cook, plus whatever extra lethality is needed to destroy more heat-resistant spoilage spores. Process calculation, F0 and the 12D concept are covered in thermal-processing-canning. Canned meats include corned beef, luncheon meat, meat curries and stews, sausages in brine and pet foods. Cured canned meats such as luncheon meat and canned ham can be given a milder heat process than uncured meats because nitrite, salt and other hurdles inhibit the outgrowth of surviving spores; some large canned hams are not shelf-stable and must be kept refrigerated, as their labels state.
Heat processing affects quality. Long retorting softens texture, can toughen lean pieces, develops cooked flavours and causes sulphide staining of uncoated cans, which is prevented by suitable lacquers. Fat separation and jelly formation in the can are controlled by formulation. Exhausting, seaming, cooling and the hygiene of cooling water are as critical for meat as for any canned food.
Drying is one of the oldest ways of preserving meat. Traditional dried meats include jerky (thin strips of lean meat, marinated and dried), biltong (salted, vinegar-treated and air-dried strips from southern Africa), pemmican (dried meat pounded with fat) and many regional products. Drying lowers water activity below the level that supports pathogens and most spoilage organisms; salt, acid and smoke add further hurdles. Because drying at low temperature may not kill pathogens, modern guidance for jerky requires a validated lethality step, cooking to a safe temperature before or during drying, followed by drying to a specified water activity.
The yield of dried meat follows from the solids balance. 50 kg of lean meat at 72% moisture dried to 20% moisture gives 50 × 0.28 ÷ 0.80 = 17.5 kg of product, ignoring losses of fat and solids. Intermediate-moisture meats, with water activity typically in the range where bacteria are inhibited but some yeasts and moulds can grow, use humectants such as salt, sugar or glycerol to lower water activity while keeping the product soft. Freeze-dried meat is used for camping, military and space rations; it rehydrates well but is costly and very susceptible to oxidation unless packed without oxygen.
Freezing preserves meat by stopping microbial growth and slowing chemical change. Fast freezing forms small ice crystals within the fibres and damages less tissue; slow freezing forms large extracellular crystals that distort and rupture fibres and increase drip loss on thawing. Meat should not be frozen pre-rigor unless it is to be cooked from frozen, because thaw rigor would cause severe shortening and drip.
During frozen storage, quality is lost mainly through lipid oxidation (rancidity), which is faster in pork and poultry than in beef because their fats are more unsaturated and is accelerated by salt, so frozen cured and salted products have short frozen lives; through freezer burn, the dry, discoloured surface patches caused by sublimation of ice where packaging is loose or permeable; and through protein denaturation that reduces water-holding capacity. Storage at a constant low temperature, commonly −18 °C or colder, in tight, moisture-proof and oxygen-barrier packaging minimises these changes. Thawing should be done under refrigeration or by other controlled methods to limit microbial growth on the surface. Freezer design and freezing time calculation are in chilling-freezing-frozen-foods.
Slaughter, scalding, defeathering, evisceration and chilling of poultry are covered in the Veterinary track (meat-science-abattoir). Further processing begins with the chilled carcass. Most poultry is now sold not as whole birds but as portions (breasts, legs, thighs, drumsticks, wings), boneless meat and processed products. Cut-up lines divide carcasses mechanically; deboning is done manually on cone lines or by machines. Timing matters for tenderness: breast meat removed from the carcass before rigor is complete contracts and becomes tough, so processors either age carcasses for several hours before deboning or use electrical stimulation to speed rigor. Poultry meat is particularly prone to PSE-like changes in breast meat after heat stress, and modern fast-growing broilers show breast myopathies such as white striping and woody breast, which reduce eating quality and processing yield.
Poultry carries Salmonella and Campylobacter, and further processing can spread them; control relies on hygienic slaughter, chilling, antimicrobial interventions where permitted, cold chain, and validated cooking for ready-to-eat products, as described in milk-meat-hygiene-food-safety.
Mechanically separated (or mechanically deboned) meat (MSM or MDM) is recovered from frames, necks and backs after the main cuts are removed, by forcing the bones and adhering meat through a sieve under pressure. It is a paste with fine texture, higher fat, haem pigments and bone marrow content than hand-deboned meat, and it contains small bone particles and more calcium. Because of its fine structure, high pigment and membrane lipids, it oxidises quickly and is usually frozen promptly and used in comminuted products such as frankfurters and nuggets. Its use and labelling are regulated, and limits on bone particle size and calcium content apply in some countries.
Marination is widely used to improve yield, juiciness, tenderness and flavour of poultry meat. Marinades containing salt and phosphates are added by injection, by tumbling under vacuum, or by soaking. The pick-up, the weight gain as a percentage of the original weight, is measured and controlled; a breast fillet of 200 g that weighs 220 g after marination has a pick-up of 10%. Retention after storage and cooking is the real measure of a marinade's performance.
Further-processed poultry products range from marinated raw portions to fully cooked ready-to-eat items. Coated products such as nuggets, tenders and patties are made from whole muscle, chopped or comminuted meat, often with mechanically separated meat, formed, coated, par-fried and frozen or fully cooked. Turkey is used for rolls, hams, pastrami, frankfurters and deli meats, cured and cooked like pork and beef products; turkey ham is made from thigh meat cured to resemble ham. Cooked products are given validated cooking to destroy Salmonella and Listeria, then chilled and packaged under conditions that prevent recontamination; post-packaging pasteurisation or high-pressure processing may be used for ready-to-eat sliced products.
A defect peculiar to cooked poultry is pinking: cooked white meat that remains pink although fully cooked, caused by nitrite or nitrate contamination (from water, vegetables or smoke), by carbon monoxide or nitric oxide from gas ovens, or by undenatured myoglobin and haem complexes at high pH. Because consumers read pink as undercooked, pinking causes complaints and rejections even though the product is safe.
A hen's egg consists of shell, membranes, albumen and yolk. By weight, the shell is roughly a tenth of the egg, the albumen about three-fifths and the yolk about three-tenths, varying with the age and strain of the hen and the size of the egg. The shell is mostly calcium carbonate in a protein matrix, perforated by thousands of pores that allow gas exchange, and covered by a thin proteinaceous cuticle that partly blocks the pores against bacteria. Inside the shell are two shell membranes; at the blunt end they separate to form the air cell as the egg cools and loses moisture. The albumen comprises an outer thin layer, a thick layer around the yolk and an inner thin layer; the chalazae, twisted cords of thick albumen, anchor the yolk in the centre. The yolk is enclosed by the vitelline membrane.
Whole egg contents are about three-quarters water, with roughly 12–13% protein and 10–11% lipid. Albumen is mostly water with about a tenth protein: ovalbumin is the main protein, with ovotransferrin (conalbumin), ovomucoid, lysozyme and ovomucin, which gives the thick albumen its gel structure. Yolk is about half solids, rich in lipids (triglycerides, phospholipids including lecithin, and cholesterol) and lipoproteins; its colour comes from carotenoids (xanthophylls) supplied by the feed.
Eggs lose quality from the moment they are laid. Carbon dioxide diffuses out through the pores, so the albumen pH rises from about 7.6 at laying to above 9 within days at room temperature. The thick albumen thins as its ovomucin structure breaks down, so a broken-out stale egg spreads over a wide area. Water moves from the albumen into the yolk, which swells, stretches the vitelline membrane, flattens and is more easily broken. Water also evaporates through the shell, so the air cell enlarges and the egg's specific gravity falls. Flavour declines. All these changes are much slower at refrigeration temperatures, which is why cooling soon after laying is the main tool of egg quality. In some countries eggs are kept refrigerated throughout marketing; in others, including the European Union, unwashed eggs are kept at stable cool temperatures but not refrigerated in retail, to avoid condensation on the shell when they are taken out.
Egg quality is assessed on the intact egg and on the broken-out egg. Candling shines a light through the egg to reveal cracks, the size of the air cell, blood and meat spots and the position and mobility of the yolk. Shell quality is measured by shell thickness, breaking strength or specific gravity (by flotation in salt solutions). The interior is assessed by breaking the egg onto a flat surface. The Haugh unit, the standard measure of albumen quality, is calculated from the height of the thick albumen (H, mm) and the egg weight (W, g) as HU = 100 log10(H − 1.7 W^0.37 + 7.57). An egg of 60 g with an albumen height of 7.0 mm has HU = 100 log10(7.0 − 1.7 × 4.55 + 7.57) = 83.5; with an albumen height of 4.0 mm, HU falls to about 58. Fresh, high-quality eggs have high Haugh units, and grading systems such as the US standards use Haugh unit bands for the top grades. The yolk index, yolk height divided by yolk width, measures how much the yolk has flattened: a yolk 18 mm high and 42 mm wide has an index of 0.43. Yolk colour is scored against colour fans. Egg grades, weight classes and the definitions of 'fresh' and 'extra fresh' are set by national or regional marketing standards and differ between countries.
Shell egg quality is preserved by prompt cooling, refrigerated or cool stable storage, and protection of the shell's barrier. Eggs are collected frequently and cooled. Washing removes dirt but can damage the cuticle; where eggs are washed, the wash water must be warmer than the egg so that water is not drawn in through the pores as the contents contract, and sanitisers are used; the European Union generally prohibits washing of class A eggs, while the United States requires washing. Oiling or coating the shell with mineral oil or other coatings partly seals the pores and slows loss of carbon dioxide and moisture; thermostabilisation, a short dip in hot water or oil, sets a thin layer of albumen under the membrane. In-shell pasteurisation, heating eggs in water baths under controlled conditions, reduces Salmonella inside the shell without cooking the egg and is used for eggs served to vulnerable groups.
Salmonella Enteritidis can infect the egg contents inside the hen, so even clean, intact eggs can carry it. Control combines flock programmes (testing, vaccination, hygiene), refrigeration that prevents its growth, and thorough cooking or pasteurisation, as described in milk-meat-hygiene-food-safety.
Egg-breaking plants break eggs mechanically, separate yolks and whites if required, filter, chill and pasteurise the liquid. Liquid whole egg is pasteurised at a temperature and time set by regulation in each country, chosen to destroy Salmonella while avoiding coagulation; the standards differ by product, because egg white proteins are much more heat-sensitive than yolk and whole egg, and salted or sugared yolk needs higher temperatures because the solutes protect the bacteria. Albumen pasteurisation therefore uses lower temperatures, sometimes with aluminium salts added to stabilise ovotransferrin or with hydrogen peroxide. Ultrapasteurised liquid egg with aseptic packaging has an extended refrigerated life.
Frozen egg products are used by bakeries and food manufacturers. Egg white and whole egg freeze and thaw without serious change, but yolk frozen below about −6 °C gels irreversibly, because ice formation concentrates and aggregates its low-density lipoproteins, giving a pasty, lumpy thawed yolk. Adding about 10% sugar or salt to yolk before freezing prevents gelation; the product is then labelled sugared or salted yolk and used accordingly, sweet products for bakery and salted for mayonnaise and dressings.
Egg powders are made mainly by spray drying pasteurised liquid egg. Whole egg, yolk and albumen powders are used in bakery, confectionery, pasta, mixes and ready meals because they are light, stable and easy to store. Egg white contains a small amount of free glucose, which during storage of the dried product reacts with the proteins by the Maillard reaction, causing browning, off-flavour and loss of solubility and whipping ability. Glucose is therefore removed before drying by desugaring: fermentation with yeast or bacteria, or treatment with glucose oxidase and catalase. Dried egg white is often heat-treated in the dry state ('hot room' treatment) to destroy Salmonella and to improve gel strength.
Powder yield follows from the solids balance: 1000 kg of liquid whole egg with 24% solids dried to a powder of 4% moisture gives 1000 × 0.24 ÷ 0.96 = 250 kg of powder. Powder quality is measured by moisture, solubility, colour, functional performance (foaming, gelling, emulsifying) and microbiological tests, especially for Salmonella. Spray-drying principles and equipment are covered in evaporation-dehydration.
A student uses this subject to answer the meat and egg questions that recur in food technology papers: why the pH falls after slaughter, what causes cold shortening, the colours of myoglobin, the difference between PSE and DFD, what nitrite does, why sausage batters must be kept cold, and why egg white is desugared before drying. In the laboratory the same student measures pH and drip loss, chops a frankfurter batter and tests its stability, cures and smokes a small ham, breaks eggs to measure Haugh units and yolk index, and works the mass balances for brine uptake, drying yield and egg powder.
Five years into a meat, poultry or egg plant, a technologist sets and defends process specifications: chilling profiles that avoid cold shortening, brine formulations and pump levels, chopping end temperatures, smokehouse cycles, cooking core temperatures and egg pasteurisation conditions within the national regulation. The same person investigates complaints of grey ham, fatting-out in sausages, pink cooked chicken, rancid frozen pork or brown egg powder, finds the cause in raw material or process, and corrects it while keeping labels, additive levels and pathogen controls in compliance.
After twenty-five years a senior manager decides what a plant makes and how: whether to invest in injection and tumbling lines, cold-set restructuring, high-pressure processing or egg drying; how to source animals and eggs that give consistent quality; how to respond to pressure to reduce salt, nitrite and phosphates without losing safety; and how to manage recalls and outbreaks linked to Listeria, Salmonella or E. coli. The manager also negotiates specifications with retailers and export markets whose rules on additives, labelling and washing of eggs differ.
A researcher with long industry experience works on the science behind these decisions: the control of post-mortem metabolism and its effect on tenderness and water holding, the genetics of meat quality defects, the chemistry of cured colour and the formation of nitrosamines and PAHs, protein functionality in batters and cold-set binders, the causes of broiler breast myopathies, the inactivation kinetics of pathogens in eggs and egg products, and alternatives to nitrite and phosphate. Such work produces the data and models that regulators and companies use to set limits and validate processes.
This manual does not give legal limits for nitrite, nitrate, phosphates or other additives, egg pasteurisation time–temperature standards, or national grade standards for eggs, because these differ by country and change; the current regulation must be read. It does not give time-to-rigor values for each species or validated cooking and drying parameters for specific products, which must be established for each process. Slaughter, stunning, carcass dressing, inspection and abattoir design are in the Veterinary track (meat-science-abattoir, milk-meat-hygiene-food-safety); freezing equipment and freezing time are in chilling-freezing-frozen-foods; thermal process calculation is in thermal-processing-canning; fish smoking and fish products are in fish-seafood-processing. Halal and kosher processing requirements and religious slaughter are covered in the Veterinary track only.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions. Every numerical answer was computed by script. Process conditions and compositions are standard textbook values that vary with species, product and plant; additive limits and egg standards differ by country.
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