Comminution
Texture is one of the most important palatability characteristics of meat. Generally, beef with the best texture characteristics is associated with the highest value parts of the carcass. This is the meat of the loin, Table 8.5. Effect of calcium chloride injection on beef quality (based on Kerth et al., 1995).
CaCl2(mM)
0 200 250
Shear force (kg) 5.6 4.7 4.4
Tenderness 5.0 5.6 5.8
Juiciness 5.4 5.9 5.7
Flavour intensity 5.9 6.2 6.3
Beef flavour 5.7 5.9 6.0
M. longissimus dorsi muscles were removed 48 h post mortem and injected with CaCl2at 5% of their weight. Shear force was measured instrumentally. The other values are mean scores from a trained taste panel using eight-point scales (8 = extremely tender, 1 = extremely tough, etc.).
sirloin, forerib, topside and fillet from young, rapidly grown animals.
However, it forms less than a third of the carcass. Meat from the remaining parts, and that from older animals, which is inherently tougher, can be comminuted. This is particularly appropriate for meat from the forequarter where the amounts of connective tissue are rela- tively high. At its simplest, the process consists of mincing or grinding the meat into small pieces, which can then be sold as ground beef or hamburger meat, or reformed by being compressed into convenient shaped products. By reducing particle size, comminution breaks up connective tissue and fat. The small pieces of meat are held together by exudate – a solution of the muscle proteins which is sticky. Binding between the meat particles can be improved by incorporating salts or other additives. By controlling the size of the meat pieces or particles, and the degree of adhesion, different textures and mouth feel can be produced. The size of the portion can also be chosen exactly and standardized to produce a consistent product.
There are other advantages to comminution. As well as enabling the modification and control of texture of meat, and increasing the economic value of lower quality parts of the carcass and trimmings from high value cuts, it leads to the potential development of meat products with similar added value. Potential problems are that, as well as as having relatively high loads of microorganisms, comminuted meat tends to lose beneficial vitamins. Comminuted meat products include burgers, reformed and restructured steaks, and sausages. They are often characterized by a relatively high fat content (Table 8.6).
Comminution methods
Comminution can be achieved by mincing (grinding), bowl chopping or flaking. The type of process affects particle size and shape, and so influences other properties. In mincing, a screw auger forces the meat through a plate against which operates a rotating knife. The size of the perforations in the plate determines the size of the particles of minced
Table 8.6. The composition of some comminuted meat products in the UK (derived from Chan et al., 1996).
Percentage Percentage Percentage Percentage
Product water protein fat carbohydrate
Beefburger 56 17 25 0.1
Beef grill steak 57 17 24 0.2
Beef sausage 55 10 24 9.4
Pork sausage 52 12 23 9.2
meat. The meat is subjected to high pressures in the auger and large shearing forces between the knife and plate. If the contact between the knife and plate is poor, or the blade is not sharp, connective tissue is not cut cleanly and can become trapped, therefore remaining unminced.
In bowl-chopping, a circular, slowly rotating bowl carries the meat into a set of rapidly rotating knives operating in a vertical plane. This can break the meat down into very fine particles, depending on the number of passes made past the blades. Bowl-chopping is also a very effective way of mixing added ingredients into the comminuted meat.
Both mincing and bowl-chopping increase the meat temperature. In bowl-chopping this can be controlled by introducing the meat at a temperature just below 0°C. In flaking, the temperature of the meat is very important and is maintained between !2°C and !4°C. A blade is used to cut flakes off the end of the frozen block of meat. The flakes have a good shape for sticking together.
Burgers
Traditionally, hamburgers are made of minced or flaked beef but nowadays other meats can also be used. Sometimes salt (sodium chloride) and ‘extenders’ such as soya protein are added to improve the cohesiveness of the burgers after cooking and reduce the cost of the product. They can also be used to reduce the fat content. In the UK the minimum allowed meat content is 80% but in the USA extenders are not permitted and hamburger meat must consist only of minced beef together with beef fat. The total fat content must also not exceed 30%
but is generally lower (15–20%). The best burgers are made from meat with a small connective tissue content. Too much connective tissue produces an undesirable texture. The minced meat is pressed or extruded into moulds to form round patties. Care is necessary not to subject it to too high shear stresses or the burgers will shrink unevenly and lose their shape on cooking.
Concern about eating large amounts of saturated fat has led to the development of low-fat burgers. These contain less than 10% fat, some fat being replaced by vegetable ‘binders’ such as soya protein, starches or carrageenan, derived from red seaweeds. These improve the WHC of the lean meat and retain some of the desirable organoleptic properties associated with fat, such as juiciness.
Reformed and restructured steaks
In reformed products, the comminuted meat is moulded into a shape resembling a natural steak. The process is a good way of upgrading the
value of beef forequarter meat. Flaked meat is used, rather than minced meat, because the particles bind together better and produce a better texture. Adhesion is promoted by the large surface area of the flakes, and the protein exuded from them. Binding is sometimes improved by incorporating salts, such as polyphosphates, or other additives.
Rather than rely on the natural adhesive properties of the meat proteins, systems have been developed in which sodium alginate is used to form a gel that binds the product together. Alginates are derived from brown seaweeds and are used as thickening agents in various foods. The gel is formed by reaction of the sodium alginate with calcium ions. Much of the success of a product depends on how closely this reaction can be controlled to produce the desired gel properties. Larger pieces of meat can also be formed into blocks of tissue using this technique. Reviews of many aspects of restructuring meat can be found in Pearson and Dutson (1987).
Sausages
Sausages are made from chopped or comminuted lean meat and fat, mixed with salt, spices and other ingredients, then filled into a con- tainer. The latter is often a casing, made from the cleaned intestines of cattle, sheep or pigs. In cleaning, much of the layered wall of the intestine is removed, leaving mainly just collagen. Artificial casings are now often used. These are made from reconstituted collagen derived from other parts of the animal, particularly the skin of cattle, and have the obvious benefit of uniformity of the product.
Fresh sausages
There are essentially three types of sausage: fresh, cooked and dry.
Fresh and cooked sausages are perishable unless refrigerated. A fresh pork sausage in the UK might be made from a mixture of lean meat (45–60%), fat (15–20%), rusk and water, together with salt and spices.
Rusk is a cereal filler, essentially made from bread dough, baked and crushed into granules, which binds together the other ingredients. The comminuted meat used to make sausages tends to carry a relatively high level of microbial contamination. To control this, sulphite or metabisulphite may sometimes be added in the UK. Many countries, however, do not allow this. The active agent is sulphur dioxide, which is particularly effective against Pseudomonas. Better-quality fresh sausages tend to contain a higher percentage of lean meat. Fresh sausages must be cooked before consumption – often by frying or grilling.
Cooked sausages
Cooked sausages, such as frankfurters and Bologna, as sold require no cooking by the consumer but can be eaten directly. Frankfurters may contain beef or veal as well as pork, and the meat is usually cured by the addition of nitrite or nitrate. Curing is described in Chapter 9. The amount of cereal used, if any, is relatively low (5% or less) and the product may be smoked before cooking. In blood sausage (black puddings), a mixture of pigs’ blood, fat and oatmeal, with salt and seasoning, is cooked in casings.
Dry sausages
Dry sausages are not normally cooked before eating but are preserved by the meat being cured with relatively large amounts of salt and by having a very low water content, and hence a low aw value (see Chapter 9). Examples are salamis and chorizos. In the case of salamis, some types are hot-smoked. Dry sausages are held for relatively long periods to develop their characteristic flavours. This is partly through the growth of various beneficial bacteria, especially lactic acid- producing types such as Lactobacillus. The lactic acid is produced during the ripening process. Lactic acid-producing bacteria are always present on meat to some degree. However, the bacteria are nowadays usually introduced as starter cultures inoculated into the sausage mix, which is held initially at quite high temperatures to promote fermenta- tion. Various additives may also be incorporated to increase the acidity of the meat, for example glucono-lactone, which is hydrolysed to gluconic acid, or lactic acid. The acidity inhibits the growth of undesirable microorganisms and reduces the WHC of the meat. The loss of water facilitates drying. In modern production systems the fermentation and drying are carefully controlled by regulating tempera- ture and humidity. A good series of papers relating to modern techno- logies used for producing cured and fermented meat products can be found in Smulders et al. (1992). The science of fermented meats is covered in Campbell-Platt and Cook (1995). An excellent source of information on all aspects of meat products is Varnum and Sutherland (1995).