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PRINCIPLES OF MEAT PROCESSING TECHNOLOGY

MEAT PROCESSING TECHNOLOGY

Meat processing technology comprises the steps and procedures in the manufacture of processed meat products. Processed meat products, which include various different types and local/regional variations, are food of animal origin, which contribute valuable animal proteins to human diets. Animal tissues, in the first place muscle meat and fat, are the main ingredients, besides occasionally used other tissues such as internal organs, skins and blood or ingredients of plant origin.

All processed meat products have been in one way or another physically and/or chemically treated. These treatments go beyond the simple cutting of meat into meat cuts or meat pieces with subsequent cooking for meat dishes in order to make the meat palatable. Meat processing involves a wide range of physical and chemical treatment methods, normally combining a variety of methods. Meat processing technologies include:

EQUIPMENT USED IN MEAT PROCESSING

In modern meat processing, most of the processing steps can be mechanized. In fact, modern meat processing would not be possible without the utilization of specialized equipment. Such equipment is available for small-scale, medium-sized or large-scale operations. The major items of meat processing equipment needed to fabricate the most commonly known meat products are listed and briefly described hereunder.

Meat grinder (Mincer) (see also page 301)


Fig. 19: Schematic drawing of grinder

A meat grinder is a machine used to force meat or meat trimmings by means of a feeding worm (auger) under pressure through a horizontally mounted cylinder (barrel). At the end of the barrel there is a cutting system consisting of star-shaped knives rotating with the feeding worm and stationary perforated discs (grinding plates). The perforations of the grinding plates normally range from 1 to 13mm. The meat is compressed by the rotating feeding auger, pushed through the cutting system and extrudes through the holes in the grinding plates after being cut by the revolving star knives. Simple equipment has only one star knife and grinder plate, but normally a series of plates and rotary knives is used. The degree of mincing is determined by the size of the holes in the last grinding plate. If frozen meat and meat rich in connective tissue is to be minced to small particles, it should be minced first through a coarse disc followed by a second operation to the desired size. Two different types of cutting systems are available, the “Enterprise System” and the “Unger System”:


Fig. 20: Grinder: Worm feed (feeding worm/auger) and cutting set with plates and knives (system "Unger")


Fig. 21: Grinder plates of different hole size, star knives and spacer rings for tightening of cutting assembly

The smallest type of meat grinder is the manual grinder (Fig. 22) designed as a simple stuffing grinder, i.e. meat material is manually stuffed into the feeder. For all these small machines the Enterprise cutting system is used with one star knife and one grinder plate. These machines are very common everywhere in food processing but their throughput and production capacity is limited due to the small size and manual operation.

The intermediate size meat grinder, also designed as a stuffing grinder, has orifice diameters up to 98 mm. It is driven by a built-in single-phase electrical motor (250 V) and available as both a table and floor model. The meat is put onto the tray and continuously fed by hand into a vertical cylindrical hole leading to the feed auger. The meat or fat is forced by its own weight into the barrel with the rotating feed auger. This type of meat grinder is the most suitable for commercial small-scale operations. Some brands use the Enterprise cutting system, others the Unger system (Fig. 23, 24).

Fig. 22: Manual grinder Fig. 23: Grinder as table model Fig. 24: Grinder as floor model

Large industrial meat grinders are driven by a three-phase electrical motor (400 V) and equipped with the Unger cutting system. The orifice cylinder diameter of this type of grinder ranges from 114 - 400 mm. Industrial grinders are either designed as stuffing grinders with either tray or hopper or as an automatic mixing grinder. The automatic mixing grinder has a big hopper and the meat falls automatically onto the mixing blades and the feeding worm (auger). The mixing blades and feeding worm can be operated independently with mixing blades rotating in both directions but the feeding worm only towards the cutting set. Most of the industrial meat grinders are also equipped with a device for separating tendons, bone particles and cartilage.


Bowl cutter (bowl chopper) (see also page 303)

The bowl cutter (Fig. 25, 26, 28, 29) is the commonly used meat chopping equipment designed to produce small or very small (“finely comminuted”) lean meat and fat particles. Bowl cutters consist of a horizontally revolving bowl and a set of curved knives rotating vertically on a horizontal axle at high speeds of up to 5,000 rpm. Many types and sizes exist with bowl volumes ranging from 10 to 2000 litres. The most useful size for small- to medium-size processing is 20 to 60 litres. In bigger models bowl and knife speed can be regulated by changing gears. Bowl cutters are equipped with a strong cover. This lid protects against accidents and its design plays a crucial role in the efficiency of the chopping process by routing the mixture flow. Number, shape, arrangement, and speed of knives are the main factors determining the performance of the cutter (see page 304). Bowl cutters should be equipped with a thermometer displaying the temperature of the meat mixture in the bowl during chopping.


Fig. 25: Small 20 litre bowl cutter, single-phase motor

Fig. 26: Bowl cutter assembled with 6 knives

Fig. 27: Bowl cutter, schematic

Fig. 29: Bowl cutter–grinder combination (twin model) with bowl cutter (60 liters capacity) and meat grinder (114 mm orifice diameter)

Fig. 28: Bowl cutter filled with meat for chopping

Fig. 30: Vacuum cutter; lid can be hermetically closed for vacuum treatment of batter in the bowl

Modern large scale bowl cutters may have devices to operate under a vacuum (Fig. 30), which helps to improve colour and texture of the meat products by keeping oxygen out of the meat mixes and avoid air pockets. Cutter knives should be adjusted to a distance of 1-2 mm from the bowl (Fig. 27) for optimal cutting (check the manufacturers recommendations for each model). Most of the large and high-speed bowl cutters are equipped with mechanical discharger devices for emptying the cutter. The process of chopping in a bowl cutter is used for producing fine comminuted products such as frankfurters, bologna, liver sausage etc., and enables processors to offer a much wider range of products.


Filling machine (“sausage stuffer”) (see also page 306)


Fig. 31: Piston stuffer, schematic

These machines are used for filling all types of meat batter in containers such as casings, glass jars, cans etc. The most common type of filling machine in small and medium size operations is the piston type. A piston is moved (Fig. 31) inside a cylinder forcing the meat material through the filling nozzle (funnel, stuffing horn) into the containers. Piston stuffers are either attached to the filling table (Fig. 32; manual) or designed as floor models (Fig. 33; hydraulic). In small-scale operations manual stuffers are usually sufficient, sometimes even simple hand-held funnels are used (Fig. 412) to push meat mixes into casings.


Fig. 32: Manual pistion stuffer (10 litres)

Fig. 33: Piston stuffer (20 litres) with different size filling funnels

Fig. 34: Principle of continuous stuffer (can also be operated with vacuum)
a = Hopper (recipient for meat mix), b = Rotating transport segments for meat mix
c = to filling nozzle; pink colour = meet mix (transport flow)

Modern filling machines for larger operations are designed as continuous vacuum stuffers (Fig. 34). During the filling process a substantial part of the enclosed air is removed from the product, which helps to improve colour and texture of the finished products. These models are usually equipped with a portioning and twisting devise and have a casing grip devise attached for filling of “shirred” (folded) uncut collagen and plastic casings. This type of continuous filling equipment is relatively expensive and are thus not used in small- to medium-size operations.

Clipping machine


Fig. 35: Manually operated sausage clipping machine with clip rails (left)

Clipping machines place small aluminium sealing clips on the sausage ends and replace the manual tying of sausages. They can be used for artificial or natural casings. Clipping machines can also be connected to filling machines. Such machines work with so called casing brakes, which are devices for slow release of the shirred casings from the filling horns ensuring tight filling. Then the filled casing segments are clipped in portions. So called double clipping machines place two clips next to each other, which ensures that the individual sausage portions remain clipped on both ends and easy separation of the sausage portions is possible. When using shirred casings (see page 263), the time consuming loading of pre-cut casings is no longer necessary. Wastage of casings can be reduced to a minimum by tight filling and leaving only as much casing for the sausage end as needed for the placing of the clips.

Clipping machines are mainly used in larger operations and in most cases operated by compressed air. For medium-scale operations manually operated hand clippers are available (Fig. 35).

Smokehouses (see also page 310)

Simple smokehouses are used for smoking only (Fig. 36, 37). In traditional and small-scale operations the most common methods of smoke generation include burning damp hardwood sawdust, heating dry sawdust or heating pieces of log. But technological progress has changed the smoke generation and application techniques. Methods used in modern meat processing include the following:



Fig. 36: Arrangement of sausages for smoking inside smokehouse, schematic

Fig. 37: Small-scale smokehouse (sawdust is placed on the smouldering tray)

Burning/smouldering of saw dust (Fig. 38)

In modern smokehouses (1), smoke generation takes place outside the smoking chamber in special smoke generators with electrical or gas ignition (4). Separate smoke generators allow better control of the quantity and temperature of the smoke produced. The sawdust or chip material (3) is moved from the receptacle to the burning zone (4) by a stirrer or shaker (3). It is ignited by means of an electrically heated plate or by gas flame. A smoke stripper, which is basically a cold water spray, can be placed in the initial part of the smoke pipe and serves to increase the purity of the smoke as undesirable substances are washed out. Smoke with a high degree of desirable smoke components can be obtained in the low temperature range of thermal destruction of saw dust beginning at around 230°C and not exceeding 400°C. The smoke is conveyed directly from the generator to the smoking chamber (Fig. 38(1), 41) via a smoke pipe (2). The burned sawdust is collected at the bottom (5).



Fig. 38: Smokehouse with generator for sawdust smoldering

Smoke generation through friction (Fig. 39)

Timber (3), which is pressed (1) against a fast-rotating steel drum (4) results in pyrolysis of the wood in the favourable temperature range of 300°C to 400°C. The flameless, light, dense and aromatic smoke contains a large proportion of desirable smoking substances and a low proportion of tars. The smoke is conveyed (2) into the smoking chamber. The creation of smoke can be commenced and completed in a matter of seconds. The operation of this type of smoke generators is usually carried out in a discontinuous manner. The smoke quantity and quality can be regulated by changing the speed and time of rotation. As this type of smoke can be produced at relatively low temperatures, it does not carry high amounts of hazardous substances such as benzopyrene (see page 40).


Fig. 39: Friction smoke generator

Smoke generation through steam (Fig. 40)

Overheated steam (3) at approximately 300°C is injected into a compact layer of sawdust (4), which causes thermal destruction of the wood and smoke is generated. This method allows the control of smoke generation temperature by choosing the adequate steam temperature. Impurities in the smoke caused by particles of tar or ash are minimal. The steam-smoke mixture condensates extremely quickly and intensively on the surface and inside the sausage products and produces the desired smoking colour and flavour. No connection to the chimney is required as smoke particles not entering the products settle down in the condensing steam. The condensed water is conducted to the effluent system. Other details of the system are: Hopper and conveyer for sawdust (1,2), smoke duct to smoking chamber (5), ashes (6).


Fig. 40: Unit for generation of smoke by steam

Combined equipment

Modern facilities can combine smoking, cooking and cooling operations for meat products in one continuous process. By means of automatic stirring systems processing parameters such as smoke generation, temperature (up to 100°C) and relative humidity (up to 100%) required to dry, smoke, or steam-cook any type of product, can be pre-set. With additional refrigerated units installed in the smokehouse, it is also possible to use it as a fermenting/ripening room for the first crucial steps in production of fermented sausages or raw ham products, where air temperature and air humidity have to be accurately controlled (see page 123, 177).


Fig. 41: Small smokehouse, inside view, air/smoke circulation forced by extraction fan on top (arrow) and recirculated through openings in double jacket side wall (arrow)

Fig. 42: Smokehouse with sausages ready for smoking

Brine injector

This equipment serves for the injection of brine into meat. Brine is water containing dissolved salt and curing substances (nitrite) as well as additives such as phosphates, spices, sugar, carrageenan and/or soy proteins (see page 179). The injection is done by introducing pointed needles into the muscle tissue. Brine injection is mainly used for the various types of ham, bacon and other whole muscle products.

Brine injectors are available in different sizes from manually operated single-needle devices (Fig. 43, 44) for small-scale operations to semi-automated brine injectors with up to 32 needles and more (Fig. 45, 46). In large machines the quantity of brine injected into the fresh meat can be determined by pre-setting of pressure and speed. It is very important that all parts of the brine injectors are thoroughly cleaned after every working session and disinfected regularly. Before the injector is used again all hoses and needles should be rinsed with warm water as particles left in the system can block the needles. Absolute cleanliness is necessary as microorganisms remaining in the system would be injected deep into the meat pieces during the operation.


Fig. 43: Brine injectors, pump driven, manually operated, with single needle (left) and multi needle device (right)

Fig. 44: Manual pump type injector (left), syringe type injector (right)

Fig. 45: Multi-needle injector, schematic
a - Main brine supply pipe, b - Brine distribution pipe, c - Injection needle, d - Meat piece to be injected, e - Sliding needle holder, f - Excess brine collection pan

Fig. 46: Multi-needle injector, semi-automated

Tumbler or Massager

Tumblers (Fig. 47) are used for the processing of meat products such as whole-muscle or reconstituted hams. Such machines resemble in principle a drum concrete mixer. A rotating drum with steel paddles inside slowly moves the meat pieces thus causing a mechanical massaging effect. This mechanical process is assisted by the addition of salt and phosphates to achieve equal brine distribution and liberates muscular protein from the meat tissue (protein extraction). The semi-liquid protein substances join the meat pieces firmly together during later heat treatment (see page 184, 185). For hygienic reasons it is important to place the tumbler below 10°C to avoid excessive microbial growth during lengthy tumbling times (more then 4 hours or even over night). In specific cases it is recommended that the tumbler should be operated refrigerated (Fig. 48, 49) or inside a cold room below -1°C, as these temperatures are best to extract as much soluble protein as possible from the muscle meat.


Fig. 47: Tumbler, schematic

Fig. 49: Tumbler inside mobile refrigerated housing

Fig. 48: Tumbler with double jacket for refrigeration and vacuum pump/motor device

Vacuum packaging machine

For vacuum packaging the meat product has to be placed into a vacuum bag (multi-layer synthetic bag, see page 270). Air is removed from the bag by means of the vacuum packaging machine (Fig. 50) and the bag then sealed (see page 273). Special vacuum packaging machines can operate with so called gas-flushing, where a mixture of gas is injected after evacuating the air. Such protective gas atmospheres inside the product package inhibit bacterial growth and stabilize the meat colour. The gas mixtures usually contain CO2 and N2 (see page 275).


Fig. 50: Vacuum packaging machine (table model)

Mixer / blender

Mixers are used to blend meat and spices, or coarse and finely chopped meat. The machine generally consists of a rectangular or round bottom vessel through which two parallel shafts operate (Fig. 51). Various paddles are mounted on those shafts to mix the meat. The mixer is discharged through tilting by 90 degrees. Some mixers are designed as vacuum mixers (Fig. 52), as the mixing under vacuum (exclusion of oxygen) has advantages for the development of desirable product colour and texture.


Fig. 51: Blender, schematic

Fig. 52: Blender with lid for hermetic closure for vacuum treatment; can be declined for emptying

Emulsifying machine (colloid mill)


Fig. 53: Emulsifying machine, schematic

The emulsifier (Fig. 53, 54) serves for the preparation of very fine meat emulsions. Its functional parts are a perforated plate, attached to which two edged blades are rotating (rotor blade) (Fig. 55). Next to the blades there is a centrifugal pump that forces the pre-ground meat through the perforated plate. Most emulsifiers are vertical units. Compared to the bowl cutter the emulsifier operates at much higher speed, producing a finer emulsion-like mix. The emulsifier is also perfectly suited to produce semi-processed products such as pig skin emulsions (see page 32).


Fig. 54: Emulsifying machine ( top down view)

Fig. 55: Emulsifying machine (plate and rotating blade)

Ice flaker


Fig. 56: Ice flaker with storage compartment

In these machines (Fig. 56) ice flakes are continuously produced from potable water. Ice is needed in meat processing for some types of meat products. Water, added in the form of ice, is an important ingredient in order to enhance protein solution (see page 128) and to keep the temperature of the meat batter low. Ice flakers with in-built UV-water-disinfection device are available for areas with unsafe water supply.

Frozen meat cutter


Fig. 57: Frozen meat cutter with rotating round knives for cutting out pieces/chips from frozen meat blocks

The purpose of cutting frozen meat blocks into smaller pieces is to make frozen meat suitable for immediate comminuting in grinders, bowl cutters etc. without previous thawing. There are two types of machines for the cutting of frozen meat blocks, working either with knives cutting in vertical direction (guillotine principle) or using rotating drums with attached sharp knives. In the guillotine-type machines a knife head is driven hydraulically and even the hardest frozen products can be cut into small pieces, either meat cubes or meat strips. Rotary frozen meat cutters (Fig. 57) operate according to the principle of carving out particles from the frozen meat blocks. The rotary drums can be equipped with knives capable of cutting out pieces of frozen meat from large fist-size to small chip-size.

MEAT PROCESSING TECHNOLOGIES – STANDARD PRACTICES

Meat processing technologies include on the one hand purely technical processes such as

On the other hand, chemical or biochemical processes, which often go together with the technical processes, are also part of meat processing technology such as

These processes are described hereunder and in the following chapters.


1. Cutting (reducing meat particle size)

There are five methods of mechanical meat cutting for which specialized machinery is used:

Mincing (grinding) of lean and fatty animal tissues (Fig. 58)

Larger pieces of soft edible animal tissues can be reduced in size by passing them through meat grinders. Some specially designed grinders can also cut frozen meat, others are equipped with devices to separate “hard” tissues such as tendons and bone particles from the “soft” tissues (minced muscle meat particles) (see page 18, 301).

Chopping animal tissues in bowl cutter (discontinuous process) (Fig. 59)

Bowl cutters are used to chop and mix fresh or frozen lean meat, fat (and/or edible offal, if required) together with water (often used in form of ice), functional ingredients (salt, curing agents, additives) and extenders (fillers and/or binders) (see page 20, 111, 137, 151, 157)


Fig. 58: Mincing of raw meat material for processed meat products in meat grinders

Fig. 59: Chopping of meat mixture in bowl cutter; lid opened after finalizing chopping, cutter knives visible

Chopping animal tissues in emulsifying machines (continuous process)

The animal tissues to be emulsified must be pre-mixed with all other raw materials, functional ingredients and seasonings and pre-cut using grinders or bowl cutters. Thereafter they are passed through emulsifiers (also called colloid mills) in order to achieve the desired build-up of a very finely chopped or emulsified meat mix (see page 30).

Frozen meat cutting

Boneless frozen meat blocks can be cut in slices, cubes or flakes by frozen meat cutters or flakers. The frozen meat particles (2-10 cm) can be directly chopped in bowl cutters without previous thawing thus avoiding drip losses, bacterial growth and discoloration which would happen during thawing (see page 31). For small operations the manual cutting of frozen meat using cleavers or axes is also possible.

Cutting of fatty tissues

Back fat is cut in cubes of 2-4 cm on specialized machines to facilitate the subsequent chopping in cutters/emulsifiers. In small-scale operations this process can be done manually.

2. Salting / curing

Salting – Salt (sodium chloride NaCl) adds to the taste of the final product. The content of salt in sausages, hams, corned beef and similar products is normally 1.5-3%. Solely common salt is used if the cooked products shall have a greyish or greyish-brown colour as for example steaks, meat balls or “white” sausages (see box page 33). For production of a red colour in meat products see “Curing” (page 34).

Chemical aspects of salting

The water holding capacity of meat can be increased with the addition of salt up to a concentration of about 5% in lean meat and then decreases constantly. At a concentration of about 11% in the meat, the water binding capacity is back to the same level as in fresh unsalted meat.

Sodium chloride has only a very low capacity to destroy microorganisms, thus almost no bacteriological effect. Its preserving power is attributed to the capability to bind water and to deprive the meat of moisture. The water loosely bound to the protein molecules as well as “free” water will be attracted by the sodium and chloride ions causing a reduction of the water activity (aw) (see page 323) of the product. This means that less water will be available and the environment will be less favourable for the growth of microorganisms. Bacteria do not grow at a water activity below 0.91, which corresponds to a solution of 15g NaCl/100 ml water or about 15% salt in the product. These figures explain how salt has its preservative effect. Such salt concentrations (up to 15%) are too high for palatable food. However, for the preservation of natural casings this method is very useful

Heat treatment of meat salted with NaCl results in conversion of the red meat pigment myoglobin (Fe+2) to the brown metmyoglobin (Fe+3). The colour of such meat turns brown to grey (see Fig. 60, 61).

Besides adding to flavour and taste, salt also is an important functional ingredient in the meat industry, which assists in the extraction of soluble muscle proteins. This property is used for water binding and texture formation in certain meat products (see page 129, 184).

The preservation effect, which is microbial inhibition and extension of the shelf-life of meat products by salt in its concentrations used for food (on average 1.5-3% salt), is low. Meat processors should not rely too much on this effect (see box page 33) unless it is combined with other preservation methods such as reduction of moisture or heat treatment.

Curing – Consumers associate the majority of processed meat products like hams, bacon, and most sausages with an attractive pink or red colour after heat treatment. However experience shows that meat or meat mixes, after kitchen-style cooking or frying, turn brownish-grey or grey. In order to achieve the desired red or pink colour, meat or meat mixes are salted with common salt (sodium chloride NaCl), which contains a small quantity of the curing agent sodium nitrite (NaNO2). Sodium nitrite has the ability to react with the red meat pigment to form the heat stable red curing colour (for details see box page 35, 68). Only very small amounts of the nitrite are needed for this purpose (Fig. 60, 61, 88).


Fig. 60: Pieces of cooked meat (pork) 4 pieces with common salt only (right) and 3 with common salt containing small amounts of nitrite (left)

Fig. 61: Two sausage cuts One produced with salt only (right) and the other with salt and small amounts of nitrite (left)

Nitrite can be safely used in tiny concentrations for food preservation and colouring purposes. Traces of nitrite are not poisonous. In addition to the reddening effect, they have a number of additional beneficial impacts (see below) so that the meat industries widely depend on this substance. Levels of 150 mg/kg in the meat product, which is 0.015%, are normally sufficient.

To reduce the risk of overdosing of nitrite salt, a safe approach is to make nitrite available only in a homogeneous mixture with common salt generally in the proportion 0.5% nitrite and the balance of sodium chloride (99.5%). This mixture is called nitrite curing salt. At a common dosage level of 1.5-3% added to the meat product, the desired salty flavour is achieved and at the same time the small amount of nitrite needed for the curing reaction is also provided. Due to the sensory limits of salt addition (salt contents of 4% are normally not exceeded), the amounts of nitrite are kept low accordingly.

Chemical and toxicological aspects of curing

In meat or meat mixes to be cured the nitrite curing salt must be evenly distributed (relevant techniques see page 37, 38, 39, 134, 173, 179)). During mixing the nitrite is brought in close contact with the muscle tissue and its red meat pigment, the myoglobin. Due to the acidification in meat after slaughter (see page 4), the pH of such meat or meat mixes is always below 7, which means slightly acidic. The acidity may be enhanced through curing accelerators such as ascorbic acid or erythorbate (see page 37, 68).

Nitrite (NaNO2), or rather nitrogen oxide, NO, which is formed from nitrite in an acid environment, combines with myoglobin to form nitrosomyoglobin, a bright red compound. The nitrosomyoglobin is heat stable i.e. when the meat is heat treated the bright red colour remains. The addition of nitrite curing salt in quantities of approximately 2%, which is the usual salt level, generates a nitrite content in the meat products of approximately 150ppm (parts per million or 150 mg/kg). This nitrite content is not toxic for consumers. Upon reaction of the nitrite with the myoglobin (which is the genuine curing reaction), there will be on average a residual level of nitrite of 50-100ppm remaining in the product. In any case the amount of residual nitrite in the finished product should not exceed 125ppm. The maximum ingoing amount for processed meat products is normally up to 200mg/kg of product (Codex Alimentarius, 1991).

Apart from its poisoning potential (which is unlikely when using nitrite curing salt), there is a debate concerning the possible health hazards of nitrite curing as under certain conditions nitrite can form nitrosamines, some of which can be carcinogenic in the long term. However, nitrosamines can only be found in strongly cooked or fried meat products which were previously cured with nitrite. Fresh meat for cooking (see page 90) and fresh burgers or sausages for frying (see page 103) do usually not contain nitrite but salt only. Hence the risk of formation of nitrosamines does not exist in such products. One product, where such conditions may be met, is bacon. Keeping the residual nitrite content low in bacon minimizes the risk of formation of nitrosamines.

Sodium or potassium nitrate (Na/KNO3) (“saltpetre”) may also be used for curing but it is limited to certain dry cured products such as raw hams, which require long curing and aging periods. Nitrate must be broken down by bacteria to nitrite, which is the substance to react through its NO with the muscle pigment myoglobin. The bacterial process is rather slow and time consuming. As most products require an immediate curing effect, the nitrite is the substance of choice in most cases and there is little use for nitrate (see also page 119).

A great deal of research has been done with regard to the utilization of nitrite and it can be said that nitrite in meat products is safe if basic rules (see box page 35) are adhered to. Nitrite is now recognized a substance with multifunctional beneficial properties in meat processing:

Many attempts have been made to replace nitrite by other substances, which would bring about the same beneficial effects as listed above. Up to now no alternative substance has been found. As the above desirable effects are achieved with extremely low levels of nitrite, the substance can be considered safe from the health point of view. Currently the known advantages of nitrite outweigh the known risks.

Curing of chopped/comminuted meat mixtures

Curing is applied for most chopped meat mixtures or sausage mixes for which a reddish colour is desired. The curing agent nitrite is added in dry form as nitrite curing salt (Fig. 62). The reaction of nitrite with the red meat pigment starts immediately. Due to homogenous blending the meat pigments have instant contact with the nitrite. Higher temperatures during processing, e.g. “reddening” of raw-cooked type sausages at 50°C or scalding/cooking of other products at 70-80°C, accelerate the process.


Another accelerating or “catalytic” effect is the addition of ascorbic acid, which slightly lowers the pH of the meat mixture. However, the dosage of ascorbic acid must be low (0.05%), just to provide the slightly acid conditions for the reduction of NaNO2 to NO. A pronounced reduction of the pH would negatively affect the water binding capacity of the product which is not desirable.


Fig. 62: Adding of nitrite curing salt during initial phase of meat mix fabrication

Curing of entire meat pieces

Besides the curing of chopped meat mixtures, entire pieces of muscle meat can be cured. However, due to size the curing substances cannot instantly react with the meat pigments as is the case in chopped meat mixes. Hence various curing techniques are applied.

The final products of curing entire meat pieces are either cured raw fermented products or cured cooked products (see page 98). The curing system to be used depends on the nature of the final product (uncooked or cooked). There are two systems for curing entire meat pieces, dry curing and wet curing (“pickling”) and the type of the final product determines which system will used.

In dry curing a curing mix is prepared containing salt or nitrite curing salt, together with spices and other additives. The pieces of meat are rubbed with this curing mix (Fig. 63, 64, 214, 215) and packed in tanks. The curing mix gradually permeates into the meat, which can be a lengthy process ranging from several days to several weeks. For more details see page 173).

Dry curing is exclusively used for the fabrication of cured raw fermented products, in particular those with a long ripening period.


Fig. 63: Application of dry curing mix (curing salt, curing accelerators, spices) on fresh ham (pork leg)

Fig. 64: Ham is uniformly covered by curing mix

The second method of curing meat pieces is wet curing, also called pickling, which involves the application of curing brine to the meat. For the manufacture of the brine, curing salt and spices, and other additives if required are dissolved in water (see page 179). The meat cuts are packed in tanks and brine is added until all pieces are completely covered (Fig. 65). A temperature of +8 to +10°C for the curing room is recommended as lower temperatures may retard curing. For equal penetration of the brine, the meat is cured for periods ranging from several days to two weeks depending on the size of the cuts and curing conditions. After completion of the curing, ripening periods for the products follow for taste and flavour build-up (for more details see page 175).


Fig. 65: Wet curing

Wet curing by immersion of meat pieces in brine is primarily used for the fabrication of cured raw fermented products with shorter ripening periods.

An alternative and quick way of wet curing is to accelerate the diffusion of the curing substances by pumping brine into the meat tissue (“injection curing”). For this purpose brine injectors with perforated hollow needles are used. The injection of brine into the muscles can be done manually by using simple pumping devices (Fig. 43, 44, 66, 67). At the industrial level semi-automatic multi-needle brine injectors (Fig. 45, 46, 68) are used which achieve very even distribution of the curing ingredients and can reduce the curing period (equal distribution of the curing substances or “‘resting period”) to less than 48 hours.


Fig. 66: Manual brine injection using a large syringe

Fig. 67: Brine injection with a manual curing pump

Fig. 68: Multi-needle brine injection (principle)

In addition, most injection cured meat pieces which are to be processed into cured-cooked products (such as cooked hams etc), are submitted to a tumbling process (see page 28, 184). Tumbling further accelerates the brine penetration throughout the meat prices and “resting periods” are not necessary.

Wet curing by brine injection is used for the fabrication of cured cooked products (see page 177).

3. Smoking

Smoke for treatment of meat products is produced from raw wood. Smoke is generated through the thermal destruction of the wood components lignin and cellulose. The thermal destruction sets free more than 1000 desirable or undesirable firm, liquid or gaseous components of wood.

These useful components contribute to the development of the following desirable effects on processed meat products:

The most known undesirable effect of smoking is the risk of residues of benzopyrene in smoked products which can be carcinogenic if the intake is in high doses over long periods. With normal eating habits, a carcinogenic risk is normally not associated with moderately smoked food such as smoked meat products.

Depending on the product, smoke is applied at different temperatures. There are two principal smoking techniques:

The principle of both methods is that the smoke infiltrates the outside layers of the product in order to develop flavour, colour and a certain preservation effect.

Cold Smoking – This is the traditional way of smoking of meat products and was primarily used for meat preservation. Nowadays it serves more for flavour and colour formation, for example in sausages made from precooked materials such as liver sausage and blood sausage (see page 153, 161).

The combination of cold smoking and drying/ripening can be applied to fermented sausages (see page 124) and salted or cured entire meat pieces (see page 176), in particular many raw ham products. In long-term ripened and dried hams, apart from providing colour and favour, the cold smoking has an important preservative effect as it prevents the growth of moulds on the meat surfaces.

The optimal temperature in “cold” smoking is 15 to 18°C (up to 26°C). Sawdust should be burned slowly with light smoke only and the meat hung not too close to the source of the smoke. Cold smoking is a long process which may take several days. It is not applied continuously, but in intervals of a few hours per day.

Hot Smoking – Hot smoking is carried out at temperatures of +60 to 80°C. The thermal destruction of the wood used for the smoking is normally not sufficient to produce these temperatures in the smoking chamber. Hence, additional heat has to be applied in the smoking chamber.


Fig. 69: Hotdogs are placed in the smokehouse for hot smoking (pale colour before smoking)

Fig. 70: After completion of the smoking process (brown-red colour after smoking, see also Fig. 42)

The relatively high temperatures in hot smoking assure a rapid colour and flavour development. The treatment period is kept relatively short in order to avoid excessive impact of the smoke (too strong smoke colour and flavour).

Hot smoking periods vary from not much longer than 10 minutes for sausages with a thin calibre such as frankfurters to up to one hour for sausages with a thick calibre such as bologna and ham sausage and products like bacon and cooked hams (see pages 142, 143).

Products and smoking – Cold smoking is used for fermented meat products (raw-cured ham, raw-fermented sausage) and precooked-cooked sausage (liver and blood sausages). Hot smoking is used for a range of raw-cooked sausages, bacon and cooked ham products. Smoke treatment can only be applied, if meat the products are filled in casings permeable to smoke (see page 248, 261). All natural casings are smoke permeable, as are cellulose or collagen basis synthetic casings.

Smoke permeable casings can also be treated using a new technology, where a liquid smoke solution is applied on the surface. This can be done by dipping in solution, showering (outside chamber) or atomization (spraying inside chamber). Polyamide or polyester based synthetic casings are not permeable to smoke. If smoke flavour is wanted for products in such casings, small quantities of suitable smoke flavour (dry or liquid) are added directly to the product mix during manufacture.

Production of liquid smoke

Liquid smoke can be used as an ingredient to sausages in smoke impermeable casings in order to achieve a certain degree of smoke flavour. As impermeable casings do not allow the penetration of gaseous smoke, liquid smoke can be added to the sausage mix during the manufacturing process. The starting point for the production of liquid smoke is natural smoke, generated by burning/smouldering wood under controlled temperatures with the input of an air supply. There are basically two different methods used for the subsequent processing of liquid smoke:

  • direct condensation of natural wood smoke to liquid smoke
  • penetration of the smoke into a carrier substance on the basis of water or oil and using this "smoked" carrier substance as an ingredient for meat products

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