Module 2. Definition, standards, classification, nutritive value and basic principles of cheesemaking

Lesson 5

5.1 Introduction

Cheese is the most diverse group of dairy products and is, arguably, the most academically interesting and challenging. While many dairy products, if properly manufactured and stored, are biologically, biochemically and chemically very stable, cheeses are, in contrast, biologically and biochemically dynamic, and consequently, inherently unstable. Throughout manufacture and ripening, cheese production represents a finely orchestrated series of consecutive and concomitant biochemical events. These, if synchronized and balanced, lead to products with highly desirable flavors and body and texture, but when imbalanced, result in off-flavors. Considering that the same raw material (milk) is subjected to a manufacturing protocol whose principles are common to most cheese varieties, it is fascinating that such a diverse range of products can be produced. No two batches of the same variety and indeed no two cheeses are identical. A further important facet of cheese is the range of scientific disciplines involved. Cheese manufacture and ripening involves the chemistry and biochemistry of milk constituents, fractionation and characterization of cheese constituents, microbiology, enzymology, molecular genetics, flavor chemistry, rheology and chemical engineering.

Cheese consists of a concentration of the constituents of milk, principally fat, casein and insoluble salts, together with water in which small amounts soluble salts, lactose and albumin are found. To retain these constituents in concentrated form, milk is coagulated either by means of lactic acid produced by bacteria or by the addition of rennet or by both. A portion of water is removed by cutting, cooking, stirring or draining the curd or by mechanical application of pressure. The cheese may or may not be ripened; the nature of the process depends upon the particular variety of cheese.

The hundreds of varieties differ very much in size, shape, color, hardness, texture, odour and taste. However, all cheeses, irrespective of country of origin and method of manufacture possess certain common characteristic steps as follow:

1. They are made from the milk (or derivatives of milk) of certain mammals derivatives

2. Souring

3. Clotting by rennet or a similar enzyme preparations

4. Cutting or breaking up of the coagulum to release the whey

5. Consolidation or matting of the curd

6. Maturing

The above traits are common to all cheeses, but the conditions vary considerably. The chief factors responsible for differences in the final cheese are:

1. Type of milk used

2. Degree of souring and type of souring organisms added

3. Temperature of renneting and subsequent cooking or scalding of the curd in the whey

4. Milling and salting of the curd before putting in the hoop or mould

5. Pressure applied to the green cheese

6. Time, temperature and relative humidity of ripening

7. Special treatments such as stabbing the cheese, bathing in the brine and surface treatment to produce a certain type of coat.

5.2 Outlines of Cheese Manufacture

Cheese manufacture involves the controlled syneresis of the rennet milk coagulum, the expulsion of moisture being affected by: i) acid development, the pH falling from 6.6 to about 5.0 as a result of lactic acid bacteria of the starter, chiefly Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris, ii) warmth, the temperature being raised to about 31°C for renneting and to about 38°C for scalding the curd, and especially iii) repeated cutting of the curd and stirring.

Although some soft cheese varieties are consumed fresh, i.e. without a ripening period, the production of the vast majority of cheese varieties can be subdivided into two well-defined phases, manufacture and ripening.


The manufacturing phase might be defined as those operations performed during the first 24 h, although some of these operations, e.g. salting and dehydration, may continue over a longer period. Although the manufacturing protocol for individual varieties differ in detail, the basic steps are common to most varieties. These are acidification, coagulation, dehydration (cutting the coagulum, cooking, stirring, pressing salting and other operations that promote gel syneresis), shaping (moulding and pressing), and salting. During the dehydration process of cheese manufacture, the fat and casein in milk are concentrated between 6-12 fold, depending on the variety. The degree of dehydration is regulated by the extent and combination of the above five operations, in addition to the chemical composition of milk. In turn, the levels of moisture and salt, and pH and cheese microflora regulate and control the biochemical changes that occur during ripening and hence determine the flavor, aroma and texture of the finished product. Thus the nature and quality of the finished cheese are determined to a very large extent by the manufacturing steps. However, it is during the ripening phase that the characteristic flavor and texture of the individual cheese varieties develop.


Fig. 5.1 General protocol for cheese manufacture

5.3 Selection of Milk

The quality of milk has a profound effect on the quality of cheese made from it. The composition of cheese is strongly influenced by the composition of the milk, especially the content of fat, protein, calcium and pH. The constituents and composition of milk are influenced by several factors, including species, breed, individual variations, nutritional status, health and stage of lactation of milk-producing animals. Owing to major compositional abnormalities, milk from cows in the very early or late stage of lactation and those suffering from mastitis should be excluded. Somatic cell (leucocyte) count is a useful index of quality. It is safe to say that all changes brought about by mastitis are bad from cheese making standpoint. The bad effect of mastitis is due almost entirely to the changes in the chemical composition of the milk. The firmness of the rennet coagulum or cheese curd is enhanced by: a) acidity, b) high calcium and c) high casein content. It is reduced by alkalinity, low casein, high albumin plus globulin and high sodium. Mastitis nearly always changes the composition of milk in this direction and so leads to weak curd formation. Some genetic polymorphs of the milk proteins have significant effect on cheese yield and quality and there is increasing interest in animal breeding for desirable polymorphs. The milk should be free of taints of chemicals and free fatty acids that cause off-flavors in the cheese, and antibiotics that inhibit bacterial cultures.

A major cause of variation in the characteristics of cheese is the species of dairy animals from which milk is obtained. The principal dairying species are cattle, buffalo, sheep and goats, which produce 85%, 11%, 2% and 2% of commercial milk, respectively. Goats and sheep are significant producers of milk in certain regions, e.g. around the Mediterranean, where their milk is used mainly for the production of fermented milks and cheese. Many world famous cheeses are produced from sheep’s milk, e.g. Roquefort and Feta and Romano; traditional Mozzarella is made from buffalo milk. There are very significant differences in the composition and physicochemical properties of milk, which are reflected in the characteristics of cheese, produced therefrom. Some varieties are always made from the milk of a particular mammal. Whereas the caseins of all tyrogenic milk (capable of being converted into cheese) are much the same, the fats of this milk may differ significantly in the proportions of the fatty acids in the triglycerides. The medium chain (C6-C10) fatty acids liberated during ripening are markedly more ‘peppery’ or biting in flavor than the very short (C2-C4) or longer (C12-C18) fatty acids. As it is known that cheese flavor is due to fat break down, it might be expected that varieties made from the milk of those mammals containing a higher proportion of C6-C10 fatty acids would develop a characteristic peppery flavor, as seen in Roquefort, which is always made from sheep milk. There are significant differences in milk composition between breeds of cattle, which influence cheese quality.

The milk should be of good microbiological quality, as contaminating bacteria are concentrated in the curd and may cause defects or public health problems. However, cheese milk is usually pasteurized or subjected to alternate treatments to render it free of pathogenic, food poisoning and/or spoilage bacteria.

5.4 Inhibitory Substances in Milk

All cheeses depend on the growth of lactococci and all matured cheese depends on the development of lactobacilli. It has been known for a long time that milks behave differently in the way lactic acid bacteria grow in them. Most important in cheese making is the slow growth of Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris in some milk, especially raw milks. One of the factors may be the presence of a group of inhibitory substances naturally occurring in milk. It has been reported that a substance called lactenin found in milk may inhibit the growth of certain streptococci. Lactenin has been shown to have two components, L1 and L2. L1 is present in colostrum and is inactivated by heating to 70°C for 20 min and L2 present in mid-lactation milk and is inactivated by heating to 70°C for 20 min.

The presence of antibiotics in milk has been a major cause of trouble in cheese making. Penicillin and other antibiotics used to control mastitis in cows find their way into milk and inhibit the growth of starter organisms. The best method to control this problem is to exclude such milk for cheese making. Alternatively, starters resistant to antibiotics should be used. Also enzymes such as penicillinase can be used to neutralize the antibiotics.

Preservatives like formalin, hypochlorite, quaternary ammonium compounds and other disinfectants present in milk may inhibit the growth of starter organisms.

5.5 Storage of Chilled Milk

In modern commercial practice, particularly in Western countries milk for cheese is normally chilled to 4-5°C immediately after milking and may be held at about this temperature for several days on the farm and at the factory. Apart from the development of an undesirable psychrotrophic microflora, cold storage causes physicochemical changes (e.g. shift in calcium phosphate equilibrium and dissociation of some micellar caseins), which have undesirable effects on cheese making properties of milk.

5.6 Standardization of Milk

The composition of cheese is prescribed in ‘Standards of Identity’ with respect to moisture and fat in dry matter, which in effect defines protein:fat ratio. Fat and casein together with moisture left in the curd control cheese yield, but fat also has a marked influence on appearance and feel of the curd and cheese. When ratio of casein to fat is high, the curd is more leathery and the final cheese does not acquire the mellow, velvetiness of a whole milk cheese. Skim milk cheeses are usually consumed ‘green’. In general, the casein:fat ratio (C/F ratio) in milk should be about 0.7 for good quality cheese. Depending on the ratio required, it can be modified by:

• Removing some fat by natural creaming or centrifugation,

• Adding skim milk,

• Adding cream,

• Adding milk powder, evaporated milk or ultrafiltration retentate.

Such additions also increase the total solids content of the milk and hence increase the yield of cheese curd per unit volume.

5.7 Heat Treatment of Milk

Traditionally, cheese was made from raw milk, a practice that was almost universal until the 1940s. Although cheese made from raw milk develops more intense flavor than that produced from pasteurized milk, the former is less consistent and poses a public health risk. When cheese was produced from fresh milk on farms or in small, local factories, the growth of contaminating microorganisms was minimal but as these factories became larger, storage of milk for longer periods became necessary and hence the microbiological quality of milk deteriorated and varied. Thermization of cheese milk is fairly widely practised on receipt at the factory to reduce the microbial load and extend the storage period. Pasteurization of cheese milk became widespread about 1940, primarily from public health reasons, but also to provide a milk supply of more uniform bacteriological quality. Although a considerable amount of cheese is still produced from raw milk, especially in Southern Europe (including such famous varieties as Swiss and Emmental) pasteurized milk is generally used, especially in large factories.

Pasteurization alters the indigenous microflora and facilitates the manufacture of cheese of more uniform quality, but unless due care is exercised, it may damage the rennet coagulability and curd-forming properties of milk. Even when properly pasteurized, Cheddar cheese (and probably other varieties) made from pasteurized milk develops a less intense flavor and ripens more slowly than raw milk cheese. Several heat induced changes, e.g. inactivation of indigenous milk enzymes, killing of indigenous microorganisms, denaturation of whey proteins and their interaction with micellar қ-casein, perhaps even shifts in salt equilibria and destruction of vitamins, could be responsible for these changes. Until now it has not been possible to establish which of these factors was principally responsible for the differences in quality between raw and pasteurized milk cheese. Therefore, normally sub pasteurization temperature is preferred to heat cheese milk, which is termed as ‘thermization’. Thermization (65°C/15 s) of cheese milk on arrival on factory is common or standard practice in some countries. The objective is to control psychrotrophs and milk is normally pasteurized before cheese making.

5.8 Ripening of Milk (Acidification)

The increase in acidity in the milk to be used for cheese making known as ‘ripening’ is usually brought about by starter culture. Acidity developed inhibits the growth of undesirable organisms and influences the rate of coagulation. When the desired acidity (0.01% increase) is reached, most varieties of cheese require the addition of rennet to the ripened milk in order to obtain a curd of the desired characteristics. Acidification is normally via in situ production of lactic acid, although preformed acid or acidogen (gluconic acid-δ-lactone) are now used to directly acidify curd for some varieties, e.g. Mozzarella cheese, UF Feta and Cottage. Until recently, the indigenous microflora of milk was relied upon for acid production. Since this was probably a mixed microflora, the rate of acid production was unpredictable and the growth of undesirable bacteria led to the production of gas and off-flavors. It is now almost universal practice to add a culture (starter) of selected lactic acid bacteria to pasteurized cheese milk to achieve a uniform and predictable rate of acid production. For cheese varieties that are cooked to not more than 40°C, a starter consisting of Lactococcus lactis subsp. lactis and/or Lc. lactis subsp. cremoris is normally used while a mixed culture Streptococcus salivarus var. thermophilus, Lactobacillus spp. (L. bulgaricus, L. helveticus, L. casei) or lactobacillus culture alone is used for varieties that are ‘cooked’ to higher temperature, e.g. Swiss, hard Italian varieties.

5.9 Coagulation

The essential step in the manufacture of all cheese varieties involves coagulation of casein of milk to form a gel, which entraps the fat, if present. Coagulation may be achieved by:

• Limited proteolysis by selected proteinases (rennets)

• Acidification to pH 4.6

• Acidification to pH 5.2 and heating to 90°C.

Most cheese varieties, and about 75% of total production, are produced by rennet coagulation but some acid coagulated varieties, e.g. Quark and Cottage cheese, are of major importance. The acid/ heat coagulated cheeses are relatively minor varieties which are usually produced from rennet cheese whey and a blend of whey and skim milk and evolved as a means for recovering the nutritionally valuable whey proteins; they are usually used as food ingredients. Important varieties are Ricotta (Italy), Anari (Cyprus) and Manouri (Greece). A fourth minor group of cheese is produced not by coagulation, but by thermal evaporation of water from a mixture of whey and skim milk, whole milk or cream and crystallization of lactose (e.g. Mysost).

Rennin is milk-curdling enzyme, which is usually obtained from the fourth stomach (abomasum) of suckling calves. In other animals, the proteolytic enzyme, pepsin, substitutes rennin. Rennin is prepared commercially for use in cheese making as a salt extract of dried calf stomach. Such an extract containing the enzyme is called rennet or rennet extract.

Rennin is an extremely powerful clotting enzyme; one part of pure rennin can clot more than five million parts of milk. The optimum pH for rennin action on milk is 5.4 and for pepsin it is 2.0. However, it can function very powerfully as a clotting agent at almost neutral pH (6.2-6.4). The ratio of clotting to proteolytic power is very high in case of rennin, but is lower in case of pepsin and other proteolytic enzymes tried in cheesemaking. The latter type of enzymes result in a bitter product. For hard cheese such as Cheddar, usually about 2.5 g of commercial rennet powder is used for 100 l of milk. In case of Meito rennet it is 1.65 g/100 l milk.

The formation of curd depends upon the coagulation of the casein in milk. With rennet this occurs in two steps. The calcium caseinate in milk is first changed to the paracasein, which then combines with the calcium ions present in the milk to form an insoluble curd. This curd is elastic and when heated or pressed it will shrink, squeezing out most of the retained whey. Slow development of curd may be due to too little rennet or to the use of overheated milk. In the latter case, the addition of small amount (0.02%) of calcium chloride to the milk usually will restore the calcium ion balance and permit the normal functioning of rennin. No satisfactory substitute for rennin has been found but at times other milk clotting enzymes, such as pepsin, papain, and microbial and recombinant rennets have been used.

Rennet extract is diluted up to 20-30 times with clean potable water before added to the cheese milk. After addition of rennet, the milk is stirred for about two minutes to distribute the rennet thoroughly, and then currents are stopped in the milk with a paddle or rake. Vibration of the vat must be prevented during setting. Steam leakage into the jacket of the vat during setting should be avoided. The milk is then left undisturbed for the curd to form, and this becomes apparent in about 15 min. After about 30 min the milk is ‘set’ with a firm curd.

5.10 Post-Coagulation Processing Operations

One of the main reasons for the great interest in studying rennet coagulation is to optimize the gel cutting time. When the gel (coagulum) is firm enough, it is cut by mechanical knives in both the horizontal and vertical directions to produce curd particles. In cheese making, the cutting range between 20 and 50 min, depending on:

1. Concentration of rennet used, e.g. 20 ml of single strength rennet per 100 l milk, although this depends on the strength of the rennet used and the other coagulation conditions.

2. Whether CaCl2 is added, as this accelerates clotting (the maximum legal level in many countries is 0.2%)

3. Coagulation temperature (coagulation occurs faster at higher temperature)

4. pH (the activity of chymosin decreases with an increase in pH)

5. Seasonal changes in milk composition; e.g. late-lactation milk can be slow to clot due to its high pH and hydrolysis of caseins within the mammary gland by plasmin. Low levels of plasmin hydrolysis reduce RCT and increase the initial rate of aggregation of rennet-altered micelles although final gel strength is reduced.

6. The quality of the dilution water used to make the rennet solution prior to the addition of cheese vat, as both excessive chlorine and a high level of water hardness can adversely affect activity.

5.11 Cutting the Coagulum

The rennet gel is quite stable if maintained under quiescent conditions but if it is cut or broken, syneresis occurs rapidly, expelling whey. Syneresis concentrates the fat and casein of milk by a factor of about 6.012, depending upon the variety. The rate and extent of syneresis are influenced by milk composition, especially Ca++ and casein, pH of the whey, size of cutting of cubes, cooking temperature, rate of stirring of the curd-whey mixture and time. The composition of the finished cheese is to a large degree determined by the extent of syneresis and since this is readily under the control of the cheesemaker, it is here that the differentiation of the individual cheese varieties really begins, although, the composition of cheese milk, the amount and type of starter and the amount and type of rennet are also equally significant.

The coagulum is ready to cut after a period of from 25 min to 2 h, as defined by the recipe. The determination of exact time of cutting is very critical for the quality of cheese. However, the cheese makers’ attempts to judge the exact point of cutting are fraught with difficulties. The surface layer of coagulum is often some degree colder than the coagulum underneath and is, therefore, softer. To judge firmness of curd on the surface, therefore, has little meaning.

The main method employed by cheesemakers is to plunge the hand, rod or thermometer stem below the surface layer and to lift the coagulum causing it to break in a cleavage line. A clear cleavage with green whey at the base of the cleft indicates that the curd is ready to cut. A soft irregular cleavage with white whey indicates that the curd is too soft. The sides of the cleft show the quality of the curd. Granular curds indicate that the curd is too firm. A rule used by some cheesemakers is that the curd should be cut earlier rather than later, and once cut; the curd should be left to complete its forming process in the warmer whey which rises over it. If the coagulum becomes too firm, knives or curd breakers crush the curd rather than cut it cleanly. When curd is ready for cutting, it is first cut horizontally and then vertically. This sequence is essential to follow because if the curd is cut vertically first, slabs so made will not have sufficient strength to stand and thus, will shatter.

The curds, which have been cut cleanly, will ‘heal’ or join up the cut fibrils on the new curd surfaces and thus prevent loss of fat and other milk components. Surface-active materials such as phospholipids and whey proteins accumulate on the cut surface and form a thin osmotic membrane. This membrane controls the whey expulsion during cooking.

The fat globules are held in the matrix of the casein network, partly by physical enclosure and party by loose bonding of the globule membrane and protein. Fat globules near the cut surfaces leak away. Such fat although only 0.2-0.3% in the whey, is really 10% of the original fat in the milk and leads to loss of cheese yield. The whey from the cut curds carries water-soluble components including lactose, whey proteins, salts, peptides and other non-protein nitrogenous substances.

The size of the curds after cutting depends on type of cheese to be manufactured. Thus curds, which need to be scalded to higher temperatures, are cut into smaller pieces, while those curds, which are scalded to lower temperatures, can be left in large pieces unless the curds are very acid.

Curved-wire-strung, harp-like curd breakers are used manually in the smaller cheese dairies. The larger installations use multibladed, hand held steel knives. The blades vary from 6-18 mm apart and 76 cm long. Some cutters are composed of wires strung on steel frames.

Mechanically operated curd knives are larger than the manual knives and use either blades or wires. It is very important that the edges of the blades are kept sharp enough to cut cleanly. Heavy gauge wires tend to tear the curd more than steel knives, and some cheesemakers cut slightly earlier with wires than the knives.

Cutting the coagulum lengthwise once manually in the long rectangular vats normally cut by mechanically operated knives prevents crushing of the soft curds during the first mechanical cutting. The rotating knives in round or oval vats do not crush the curd against the vat sides. Even so, the speed of rotation in some equipment can be controlled. The angle of the blade presented to the curd is such that if the rotation of the knife is reversed it stirs rather than cuts the curd.

5.12 Cooking

The curd, when first cut, is soft and the coat surrounding the particles is open. Stirring the curd gently until the first flush of whey has left the curd particles is necessary to prevent undue crushing and loss of fat and curd dust. Once the curd coat becomes more membrane-like the agitation rate can be increased.

Cooking or scalding the curd causes the protein matrix to shrink and expel more whey. The increase in temperature also speeds up the metabolism of bacteria enclosed within the curd. Lactic acid production increases, pH declines, and acidity assists in shrinking the particles to express more whey.

Since the whey has, in solution, lactose and salts, the amount of these substances retained in the cheese is proportional to the amount of moisture in the curd. The calcium phosphate associated with the casein and in colloidal state, will gradually become solubilized as the pH falls. Thus, high acid curds (i.e. blue veined cheese curds) lose more calcium (92%) than low acid curds such as Edam (35%).

Lactose is the main metabolite of the lactic acid bacteria in the curd for the production of lactic acid. Since lactose must cross the cell wall membrane, it is not only the presence of lactose but also the strength of the lactose solution, which is a controlling factor in the metabolism of the bacteria. Thus, once the lactose concentration has decreased to a certain point, then much smaller decreases have greater effect on the growth of bacteria and on the production of lactic acid. The cheese maker has control over lactose in the curd, and, therefore, the amount of lactic acid formed, through the size of the curd particles, scald temperature and the rate of rise of temperature of the curds. There are two methods of reducing the amount of lactose in the cheese curds:

1. Shrinkage of the curds brought about by heat and lowering of the pH owing to development of lactic acid in the curd.

2. The addition of water to the whey, which increases the osmotic effect across the curd membranes and thus extracts the lactose from the curd moisture into the diluted whey.

3. The addition of hot water to the whey/ curd mixture is used as a method of scalding (heating) the curd in the washed curd cheese processes.

The aim of scalding the curd is to shrink the curd to expel moisture and so firm up the curd to a state ready for texture formation, pressing or salting. This state provides the dividing between four main groups of cheese (excluding soft cheese, some of which may be scalded).

1. The textured cheese like Cheddar, Cheshire.

2. The pasta filata types or kneaded cheese.

3. The cheese untextured in the vat stage, like Edam and Gouda cheese, and also those which acquire texture later, like Tilsiter, Emmental, etc.

4. Blue veined cheese.

The variation of scalding rates is carried out according to the acidity produced and is under the control of cheesemaker. This is a further point in the recipe where previous experience aids in interpretation. A high rate of scald will shrink the coat of the curd particles so much that the membrane is so firm that moisture is locked in the curd. The resultant cheese is acid, harsh texture, crumbly and eventually dry.

Low rates of scald may be necessary for curds in which the bacteria are slow to produce acid. Alternatively, curd shrinkage may be by acid alone without the use of scald. The recipe determines the maximum scald temperature but it is important to note that the normal lactic starter bacteria will be inhibited, if not destroyed, if the scald temperature is too high (i.e. temperature beyond 40°C). Scald temperatures higher than normal need the inclusion of high-temperature-enduring starter bacteria (i.e. S. thermophilus, L. bulgaricus, etc.). Although lactose, being soluble tends to leave the curds to be concentrated in the whey, there may be reverse movement back into the curd if the curd and whey acidities are too different.

The cheesemaker has a decision to make in respect of when to cease stirring the whey curd mixture; this is not often included in the recipe. The cessation of the stirring is called the ‘pitching’ point when the curd sinks down to the bottom of the vat.

Normally, fast acid curds are stirred until the whey is removed. With very slowly developing curds, the stirring ceases altogether and the curd is ‘pitched’, or sometimes, to prevent excessive ‘matting’ of the curd into lumps, the curds are stirred at intervals.

5.13 Curd Treatment

The manner in which the curd is handled varies in some degree according to the kind of cheese to be made. The acidity of the curd continues to increase and its body becomes firmer owing to a decrease in its content of whey. Heating the curd favors these reactions. If a soft high moisture cheese is made, the curd is removed from the vat quickly and the whey is drained. For some varieties of cheese, the curd is cut and stirred in the whey while it is being heated. For Cheddar type cheese, the curd is heated in the whey and allowed to form continuous mass, which is then cut and milled into small pieces before further processing.

The manner in which the whey is drained from the curd varies with the kind of cheese:

1. Cream cheese, for example, is prepared by placing the curd on cloths which allow the whey to drain away.

2. Sometimes the curd is placed in forms or hoops put on mats or coarsely woven screens which allow the whey to drain as in the manufacture of Brick cheese,

3. In the making of Cheddar cheese, curd is allowed to sink in the vat and the supernatant whey is drawn off,

4. In making Swiss cheese, the curd is separated by placing a cloth under the curd and lifting it out of the vat or kettle.

The rate at which the whey is allowed to drain away is determined by the kind of cheese being made. Acid continues to develop in the curd as long as appreciable amounts of whey are present. With the increase in acidity the curd becomes elastic and can be stretched or, if heated, it can be drawn out into silky strings. This is the basis of practical test used by makers of Cheddar cheese. A hot iron rod is touched to the curd, and as it is drawn away, the length of the curd fibers at their breaking point is noted, the higher the acidity the longer the threads.

5.14 Pressing

The last portion of the whey is removed from the curd by pressing. This operation is also used to mould some varieties of cheese in their conventional shape. The degree of pressure used varies with the kind of cheese.

The curd is composed of a matrix of protein enclosing fat globules, moisture, lactose, salts, non-protein nitrogenous substances, as well as peptides. The curd also contains air and some gas (CO2) so that while it is warm it is springy, elastic and soft. The fat is also mainly in the liquid state. Salt (NaCl) may or may not have been applied and salt will dissolve some of the casein surfaces, and also releases water. Thus the surface layer of casein may be rendered hard and horny if the salt is not allowed to dissolve freely into the warm curd.

Pressing the curd should, therefore, be gradual at first, because high pressure at first compresses the surface layer of the cheese and can lock moisture into pockets in the body of the cheese. The temperature of the curd before pressing should be below the liquid fat temperature, i.e. 23.9°C in summer and 26°C in winter. Otherwise, fat will leak from the curd and be lost in the whey, or will fill spaces in between the curds and give a greasy cheese. The pressure applied to the cheese should be per unit area of the cheese and not per cheese, which may vary with size. Table 5.1 shows the pressure, traditionally applied and a comparison with pressures applied to 18 kg block cheese.

Since the cheese curd holds a volume of air before pressing, those cheeses requiring very closed curds (e.g. Cheddar) have been pressed under a vacuum of 85-95 kN/m2 (25-28 in Hg). The vacuum applied for only a short time (2-3 h), also assists in cooling the curd.

Pressures have been traditionally applied for 2-3 days to Cheddar cheese, but the more recent ‘block cheese’ pressing has been limited to 24-36 h, and with vacuum pressing, 10-15 h. This has enabled the cheese mould to be washed and reused the following days.

Cheese presses are either spring, dead weight, pneumatically or hydraulically operated. Recently, the larger ‘ton’ or ‘box’ presses have been used. The presses have vacuum cylinders so that the curd can be pressed under vacuum.

One of the requirements of the pressed cheese is that the outside (rind) surface is close, smooth and with no crevices for mold penetration. The traditional methods used coarse Hessian cloths to assist in closing up the holes in the curd. Sometimes, the cheese was immersed in hot water at 48.9°C to plasticize the coat and the cheese was then repressed in stiff Calico cloth to obtain a close finish.

These systems were highly labour intensive, and textured synthetic films have replaced the cloths previously used. Traditional cheesemakers and certain cheese buyers still prefer the older methods of cheese preparation, especially for the texture cheese varieties such as Cheddar, Cheshire etc.

Table 5.1 Pressures applied to cheese of various sizes

5.15 Treatment of Rind

The manner in which the surface of the cheese is treated also influences its characteristics, for example, frequently cleaning the rind, for Cheddar.

1. Cheddar and Swiss cheeses are given a smooth and uniform surface or rind by pressing the curd while it still is warm, and curing the cheese under conditions that allow the moisture to evaporate from the surface

2. The activity of organisms on the surface is prevented in Swiss cheese by frequently cleaning the rind. For Cheddar cheese, this is done by coating the cheese with paraffin wax and holding it in a cool room with low humidity,

3. Holding them in cool, moist environment encourages the growth of mold on Camembert and Roquefort type cheeses, and the growth of yeasts and bacteria on Brick and Limburger cheeses.

The soft types of cheese acquire a rind during ripening, often as a result of the growth of molds and bacteria. Later, the evaporation of moisture hardens the rind so that it is more rigid to handle. In many instances the rind is kept clean by repeated washing with a salt impregnated cloth (e.g. Emmental) or repeated brushing to remove mould growth (e.g. Cantal). When these cheeses are ripe and ready for sale, the rind is simply coated with vegetable (olive) oil, which may be colored brown or black (e.g. Parmesan, Romano).

Smoking of cheese also gives the coat a fatty layer and has a preservative effect, due to phenolic compounds from the smoke. Spices are also used on the coats of some cheese to impart a flavor to the curd, but mainly the spices are included in the curd. Feta and similar cheeses are packed in casks or drums filled with brine or salted whey.

Gorgonzola has also been coated with Plaster of Paris as a protective coat inside a woven basket. The plaster is not completely airtight and allows the cheese to ‘breath’ and mold to remain blue.

The larger hard-pressed cheeses, like Cheddar, Emmental, etc. have in recent years been produced in block shapes for two main reasons:

1. The packing of cheese in retail markets for consumer sale in small portions has accelerated the use of block cheese shapes. These cheese blocks range from 10 to 20 kg in weight, are rectangular and can be cut mechanically without waste into consumer portions.

2. The second reason is with respect to mold or cheese mite damage, which has caused serious loss in traditional round-shaped cheese.

Attempts to overcome these defects first employed, and still use, chemical treatments, i.e. sorbic acid and its salts, or pimaricin to stop mold growth, and/or waxing or resinous coating of the cheese rind to prevent both mould growth and mite infestation.

Waxing of cheese, like Cheddar, Cheshire, etc. over the bandage requires that the bandage is completely dry (2-3 days drying). If the bandage is not dry the wax coat eels away and is not effective as mold preventive. The waxes used are available with different melting points, from 49-82°C, for either temperate or tropical usage. The application of wax is usually by dipping the cheese in a bath of melted wax for up to 30 s and then allowing it to cool quickly. It may be necessary to dip twice if the cheese is not totally covered on the first occasion.

5.16 Salting

Salting of perishable foods is among the most ancient and widely practiced techniques of food preservation. Salt has achieved universal acceptance as a mineral of great importance in trade and industry, and, in view of its preservative qualities, it has become a peculiarly appropriate symbol of fidelity in many cultures. It is, therefore, no surprise that salting is a key element in that combination of techniques that has evolved for preserving the solids of milk in the form of cheese.

Common salt (NaCl) is an ingredient of practically every variety of cheese. It may be added to subdivide cheese curds, as is the case with Cheddar and related types, or apply by immersion of the formed cheese in brine, as for Gouda, Swiss, Feta and related types. For some cheeses, the salt is rubbed on the surface after moulding is complete and, for a few types (e.g. Domiati), some or all of the salt is added to the cheese milk before curd production commences. The presence of salt in cheese and the manner of its incorporation has a significant impact on the course of the cheese fermentation, and on the final characteristics of the cheese as consumed.

The salt in cheese:

• Draws the whey out of the curd,

• Suppresses the proliferation of unwanted microorganisms, including pathogens,

• Regulates the growth of desirable organisms, including lactic acid bacteria (acidity, oxygen tension and temperature also regulate the growth of these organisms),

• Promotes physical and chemical changes in the maturing cheese,

• Directly modifies taste, and

• Serves as a factor in control of acidity.

The salt in cheese is held in solution in the aqueous phase and its concentration in solution is a strong determinant of much of the biological and biochemical changes that occur during cheese maturation. The actual level of salt in cheese varies with the type, ranging from 0.5% to about 3% (w/w) but this range is amplified by the wide differences in water content between cheese varieties, such that the concentration of NaCl in the aqueous phase may range from less than 1% to about 8%. The level of salt in cheese, the manner of its addition and the joint impact of these factors on the time needed for equilibration of the salt concentration in the aqueous phase are key determinants of varietal differences in cheese characteristics.

Within any one cheese, the distribution of salt may vary considerably according to the method of application. Dry salted cheese, such as Cheddar, should have uniform salt levels throughout the body within just a few hours after salting, whereas for brine-salted cheese, there is a marked difference between the salt content of the surface and the interior, which persists for many days or weeks, dependent on the dimensions of the cheese. Rapid attainment of salt uniformity within dry salted cheese curds generally slows or stops fermentation of the residual lactose, leaving a pool of fermentable carbohydrate to support the growth of the more salt-tolerant strains of the starter bacteria and/or the growth of the non-starter lactic acid bacteria (NSLAB), with a potentially profound impact on the course of maturation. A low internal salt level in brine-salted cheese allows for continuation of the fermentation by the added starter organisms of practically all of the lactose to lactic acid and associated end products, thus leaving little fermentable carbohydrate to support the growth of NSLAB, resulting in a different course of maturation and different flavor profiles.

5.16.1 Methods of salting

There are three main techniques for salting of cheese:

• Mixing of dry salt crystals with subdivided cheese curds prior to the moulding/pressing stage of manufacture,

• Immersion of the moulded cheese in a brine solution,

• Application of dry salt or salt slurry to the surface of the formed cheese.

For a number of varieties, a combination of these techniques is used, and for a few cheese types, salt is added either to the milk or the whey.

Brined cheeses are formed into their final size and shape prior to being immersed in a solution for a period ranging from a few hours to a few days in vat containing circulating or static brine. Static brine systems usually have un-dissolved salt at the bottom of the vats and stirring must be carried out frequently. Circulating systems have means for automatically maintaining the strength of the brine. Brine concentration typically ranges from 15% to 25% (w/w) NaCl in water and temperature may vary from about 8 to 20°C.

The salting time depends primarily on the desired salt content, and is further influenced by:

• Brine temperature (Diffusion rate increases with temperature)

• Salt concentration (Higher concentration gives faster salt uptake, but more extreme variations within the young cheese)

• Cheese dimensions (Smaller and flatter cheeses take up salt more rapidly; spherical cheeses take up salt more evenly)

• Cheese moisture and pH (Higher moisture and pH both lead to more rapid salt intake).

Last modified: Thursday, 1 November 2012, 5:50 AM