meat processing

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:

• The primary purpose of nitrite is to create a heat resistant red colour in a chemical reaction with the muscle pigment, which makes cured meat products attractive for consumers.
• Nitrite has a certain inhibitory effect on the growth of bacteria. This effect is particularly pronounced in canned meat products which are usually stored without refrigeration, where small numbers of heat resistant bacteria may have survived but their growth is inhibited by the presence of nitrite (see also page 77).
• Nitrite has the potential of attributing a specific desirable curing flavour to cured products.
• In the presence of nitrite fats are stabilized and rancidity in meat products retarded i.e., an antioxidant effect.

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:

• Meat preservation through aldehydes, phenols and acids
• (anti-microbial effect)
• Antioxidant impact through phenols and aldehydes
• (retarding fat oxidation)
• Smoke flavour through phenols, carbonyls and others
• (smoking taste)
• Smoke colour formation through carbonyls and aldehydes
• (attractive colour)
• Surface hardening of sausages/casings through aldehydes (in particular for more rigid structure of the casing)

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:

• Cold smoking
• Hot smoking

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