Tradition and basic knowledge
- Cheese has been made in most cultures since ancient times.
- Cheese is a milk concentrate, the basic solids of which consist mainly of protein (actually casein) and fat. The residual liquid is called whey.
- As a rule of thumb, the casein and fat in the milk are concentrated approximately 10 times in production of hard and some semi-hard types of cheese.
- No strict definition of the concept of cheese is possible, as so many variants exist.
- The moisture content of the cheese serves to distinguish various categories, such as hard (low-moisture), semi-hard and soft cheeses. A generally accepted classification of cheese is given in FAO/WHO Standard No. A 6.
- Each category is distinguished by a number of characteristics, such as structure (texture, body), flavour and appearance, which result from the type of milk, the choice of bacteria and the manufacturing technique employed.
- Processed cheese is a heat-treated product based on different types of cheese of varying age according to FAO/WHO Standard No. A 8 (b).
- Whey cheese is a type of cheese predominantly produced in Norway and Sweden and is defined according to FAO/WHO Standard No. A 7 as follows: Whey cheeses are products obtained by the concentration of whey and the moulding of concentrated whey, with or without the additionof milk and milk fat.
- Cream cheese is a soft unripened cheese briefly described in the FAO/ WHO Standard C 31 as "possessing a mild creamy or acid flavour and aroma typical of a milk product cultured with lactic acid and aroma-producing bacteria. It spreads and mixes readily with other foods".
Terminology for classification of cheese
(Source: Codex Alimentarius, FAO/WHO, Standard A6)
Cheese is the fresh or ripened solid or semi-solid product in which the whey protein/casein ratio does not exceed that of milk, obtained:
A By coagulating (wholly or partly) the following raw materials: milk, skimmed milk, partly skimmed milk, cream, whey cream, or buttermilk, through the action of rennet or other suitable coagulating agents, and by partially draining the whey resulting from such coagulation;
B By processing techniques involving coagulation of milk and/or materials obtained from milk that give an end product which has similar physical, chemical and organoleptic characteristics as the product systemized under Classification of cheese.
1.1 Cured or ripened cheese is cheese that is not ready for consumption shortly after manufacture, but which must be held for such time, at such temperature, and under such other conditions as will result in the necessary biochemical and physical changes characterizing the cheese.
1.2 Mould-cured or mould-ripened cheese is a cured cheese in which the curing has been accomplished primarily by the development of characteristic mould growth throughout the interior and/or on the surface of the cheese.
1.3 Uncured, unripened or fresh cheese is cheese that is ready for consumption shortly after manufacture.
Classification of cheese
The classification shown in Table 14.1 applies to all cheeses covered by this standard. However, this classification shall not preclude the designation of more specific requirements in individual cheese standards.
Cheese production – general procedures for hard and
Cheesemaking involves a number of main stages that are common to most types of cheese. There are also other modes of treatment that are specific to certain varieties. The main stages for production of hard and semi-hard cheese are illustrated schematically on the block chart in Figure 14.1.
The cheese milk is pre-treated, possibly pre-ripened after addition of a bacteria culture appropriate to the type of cheese, and mixed with rennet. The enzyme activity of the rennet causes the milk to coagulate into a solid gel known as coagulum. This is cut with special cutting tools into small cubes of the desired size – primarily to facilitate expulsion of whey.
During the rest of the curdmaking process, the bacteria grow and multiply and form lactic acid from the lactose. The curd grains are subjected to mechanical treatment with stirring tools, while at the same time the curd is heated, according to a pre-set program. The combined effect of these three actions – growth of bacteria, mechanical treatment and heat treatment – results in syneresis, i.e. expulsion of whey from the curd grains. The finished curd is placed in cheese moulds, mostly made of plastic, which determine the shape and size of the finished cheese.
The cheese is pressed, either by its own weight or more commonly by applying pressure to the moulds. Treatment during curdmaking, pressing, brining and storage conditions determines the characteristics of the cheese.
The process flow chart in Figure 14.1 also shows salting and storage. Finally, the cheese is coated, wrapped or packed.
- Fat relative to SNF (Casein) = F/SNF (Casein)
- 70-72 °C/15-20 s (not always employed)
- Cooling to renneting temperature about 30 °C
Mechanical reduction of bacteria
- Spore and bacteria removing separators
From milk to cheese
In the cheese vat
- Conditioning of cheese milk
– Calcium chloride
– Saltpetre, if permitted by law
– Starter bacteria, appropriate to type of cheese
– Rennet as coagulant
- Cutting into grains (curd)
- Removing part of the whey
- Adding water to wash curd (semi-hard cheese production)
- Heating, scalding, directly or indirectly, depending on type of cheese
- Collection of curd for pre-pressing and/or final moulding/pressing, and if required
- Brine salting or for cheddar cheese
- Cheddaring followed by milling, salting, hooping, and pressing
- Formed, pressed, and salted cheese to ripening room storage for required time
Milk treatment prior to cheesemaking
The suitability of milk as a raw material for cheese production depends largely on conditions at the dairy farm. Quite apart from the general demand for strict hygienic conditions, milk from sick cows or animals undergoing treatment with antibiotics must not be used for cheesemaking, or any other milk product.
Feeding animals on badly prepared silage can adversely affect the quality of several varieties of cheese.
With the traditional method of milk reception, i.e. morning delivery of milk in churns to the dairy in the course of a few hours of all milk needed for the day’s production, the milk was treated almost immediately after being weighed in. The fat content was then standardized in conjunction with separation and pasteurization and, after regenerative cooling to renneting temperature, the milk was pumped to the cheesemaking tanks.
The practice of collecting milk from farms at intervals of two or three days is widespread. This means that particularly stringent requirements must be met regarding the way the milk is treated by the producers. Especially a quick cooling of the collected milk to 4 °C is essential. These requirements also extend to the tanker driver, who collects the milk at the farmhouses. He must have the authority to refuse to accept milk that is even slightly affected and/or impaired by off-flavours. Bovine mastitis is a common disease that causes the cow pain as well as drastically affecting the composition and the quality of the milk; farmers must discard such milk, or at least not send it to the dairy.
Heat treatment and mechanical reduction of bacteria
When collection of milk on alternate days was introduced, cheese producers who had to use such milk noticed that the quality of the cheese frequently deteriorated. This tendency was particularly noticeable when the milk had to be stored a further day after reception, even when it was chilled to 4 °C in conjunction with transfer from road tanker to storage tank. Even longer storage times may be expected when working weeks are limited to six or even five days.
During cold storage, the milk protein and milk salts change character, which tends to impair cheesemaking properties. It has been shown that about 25 % of the calcium precipitates as phosphate after 24 hours storage at +5 °C. This reduction, however, is temporary. When the milk is pasteurized, the calcium redissolves and the coagulating properties of the milk are almost completely restored. b-casein also leaves the complex casein micelle system during cold storage, which further contributes to reducing the cheesemaking properties. However, this reduction too is almost completely restored by pasteurization.
Another equally important phenomenon is that the microflora introduced into the milk by recontamination – especially Pseudomonas spp – will adapt to the low temperature at which their enzymes, proteinases and lipases, will decompose protein and fat respectively. The result is a “bitter" flavour emanating from decomposition of the β-casein that has left the casein micelle during low-temperature storage.
The proteolytic and lipolytic enzymes formed by Pseudomonas may also co-operate to penetrate the membranes of the fat globules. This symbiotic co-operation leads to liberation of fatty acids, especially the lower ones, by lipase action, giving the milk a rancid flavour.
So, if milk that is already at least 24 – 48 hours old cannot be processed within about 12 hours after arrival at the dairy, it is advisable to chill it to about +4 °C or, preferably, thermize it.
Thermization means moderate heat treatment, 65 °C for 15 seconds, followed by cooling to +4 °C, after which the milk is still phosphatase positive. This technique was basically introduced for the purpose of arresting growth of psychrotrophic flora when milk was stored for a further 12 – 48 hours after arrival at the dairy. As mentioned in Chapter 1, the “critical age” of raw milk kept at +4 °C normally falls between 48 and 72 hours after milking. Figure 14.2 shows the arrangement of a milk reception station.
Moderate heat treatment at 65 °C for 15 s, which is often given to cheese milk.
Before the actual cheesemaking begins, the milk usually undergoes pre-treatment designed to create optimum conditions for production.
Milk intended for cheese that requires more than one month of ripening needs not necessarily be pasteurized, but usually is. National legislation often stipulates if the milk has to be pasteurized or not.
From Table 14.1, you can see that milk intended for unripened cheese (fresh cheese) must be pasteurized. This implies that cheese milk for types needing a ripening period of at least one month need not be pasteurized.
On the other hand, whey used for fodder must be pasteurized, to prevent it from spreading bovine diseases. However, if the cheese milk is pasteurized, it is not necessary to pasteurize the whey separately.
Milk intended for original Emmenthal, Parmesan and Grana, some extra hard types of cheese, must not be heated to more than 40 °C, to avoid affecting flavour, aroma and whey expulsion. Milk intended for these types of cheese normally comes from selected dairy farms with frequent veterinary inspection of the herds.
Although cheese made from unpasteurized milk is considered to have a better flavour and aroma, most producers (except makers of the extra hard types) pasteurize the milk, because its quality is seldom so dependable that they are willing to take the risk of not pasteurizing it. Pasteurization equalizes the bacterial composition of the milk from one day to the next, eliminating disturbances in an automatic or time-controlled process.
Pasteurization must be sufficient to kill bacteria capable of affecting the quality of the cheese, e.g. Coliforms, which can cause early “blowing” and a disagreeable taste. It must also kill most of the natural pathogenic bacteria.
Regular HTST pasteurization at 72 – 73 °C for 15 – 20 seconds is therefore most commonly applied. (Phosphatase negative).
However, spore-forming microorganisms in the spore state survive pasteurization and can cause serious problems during the ripening process. One example is Clostridium tyrobutyricum, which forms butyric acid and large volumes of hydrogen gas by fermenting lactic acid. The butyric acid has an unsavoury taste, and the gas destroys the texture of the cheese completely.
More intense heat treatment would reduce this particular risk, but would also seriously impair the general cheesemaking properties of the milk, as it increases the level of denatured whey proteins. This is unacceptable in terms of both quality and legal requirements. Other means of reducing thermo-tolerant bacteria are therefore used.
Traditionally, certain chemicals have been added to cheese milk prior to production to prevent “blowing” and development of the unpleasant flavour caused by heat-resistant, spore-forming bacteria (principally Clostridium tyrobutyricum). The most commonly used chemical is sodium nitrate (NaNO3), but in the production of Emmenthal cheese, hydrogen peroxide (H2O2) is also used. However, as the use of chemicals has been widely criticized, mechanical means of reducing the number of unwanted microorganisms have been adopted, particularly in countries where the use of chemical inhibitors is banned. These inhibitors can also affect some of the added bacteria in the starter culture.
Mechanical reduction of bacteria
Spore and bacteria removing separators Bactofuge
As discussed in Chapter 6.2, specially designed hermetic separators for spore and bacteria removal is used to separate bacteria, and especially the spores formed by specific bacteria strains, from milk.
The use of bacteria and spore removing separators has proved to be an efficient way of reducing the number of spores in milk, since their density is higher than that of milk. These separators normally separates the milk into a fraction that is more or less free from bacteria, and a concentrate , which contains both spores and bacteria in general and amounts to up to 3 % of the feed to the separator .
In applications where quality milk for cheese and powder production is the objective, the spore and bacteria removing separator is installed in series with the milk separator, either downstream or upstream of it.
The same temperature is often chosen for spore and bacteria removal as for separation, typically 55 – 60 °C.
There are two types of spore and bacteria removing separators:
- Two-phase type
- One-phase type
The two-phase type has two outlets at the top:
- One for continuous discharge of the heavy phase via aspecial top disc, and
- One for the spore and bacteria -reduced phase
The one-phase type has one outlet at the top of the bowl, for bacteria-reduced milk. The concentrate is collected in the sludge space of the bowl and discharged at pre-set intervals through ports in the bowl body.
These two types make it possible to choose various combinations of equipment to optimize the bacteriological status of milk used for both cheesemaking and other purposes.
It should be mentioned at this point that whey, if intended for production of whey protein concentrate as an ingredient in infant formulae, should be processed after recovery of fines and fat.
There are about ten possible ways to configure a line with spore and bacteria removing separators ; three examples are given here:
Two-phase spore and bacteria removing separator with continuous discharge of concentrate
This concept, shown in Figure 14.3, works under airtight conditions and produces a continuous flow of air-free bacteria concentrate as the heavy phase. This phase, comprising up to 3 % of the feed flow (adjusted by an external pump with variable speed control) is often sterilized and remixed with the main flow.
The sterilizer can be of different types; plate heat exchanger, tubular or infusion heater. Typical heat treatment is 120 °C for one minute, which is sufficient to inactivate spores from Clostridia microorganisms. After cooling, the concentrate can be remixed with the clarified milk before it is pasteurized at 72 °C for 15 seconds followed by regenerative cooling to the renneting temperature.
The spore and bacteria removing separator with continuous discharge of concentrate is used in applications where:
- Remixing of sterilized concentrate is possible
- There is an alternative use for the concentrate in a product where the heat treatment is strong enough to inactivate the microorganisms
At nominal capacity a spore and bacteria removing separator reduce approximately 98 % of spores from Cl. tyributyricum and 95 % of the aerobic forming spores.
One-phase spore and bacteria removing separator with intermittent discharge of concentrate
To achieve the same reduction effect as mentioned above, nominal capacities are likewise recommended. The concentrate from a one-phase spore and bacteria removing separator is discharged intermittently through ports in the bowl body at pre-set intervals of 15 – 20 minutes, which means that the collected bacteriaconcentrate will be rather concentrated and thus also low in volume, 0.15 – 0.2 % of the feed. When the concentrate is to be re-introduced into the cheese milk, it must be sterilized. This is illustrated in Figure 14.4, which also shows that before being pumped to the sterilizer, the concentrate is diluted with clarified milk milk (about 1.8% of the feed) to obtain a sufficient volume for proper sterilization. Starting and stopping of the discharge pump (5) is linked to the operation mode of the discharge system of the centrifuge. .
Where legislation does not permit re-use of the concentrate , it can be discharged to the drain or collected in a tank.
Two one phase spore and bacteria removing separators in series
To process the milk once through a spore and bacteria removing separator is not always sufficient, particularly with high spore loads in the milk. With two of these types of separatos in series reduction of Clostridia spores reaches more than 99%. Figure 14.5 illustrates a plant with two one-phase type machines in series serving one sterilizing unit.
The concentrate treatment procedure mentioned above applies here too.
Two spore and bacteria removing separators in series is sufficient (in most cases) to produce cheese without addition of bacteria-inhibiting chemicals. However, for safety reasons, during periods when very high loads of spore-formers are expected, small amounts of chemicals (2.5 – 5.0 g per 100 l of milk) may be used, if legally allowed.
It has been known for a long time that a membrane filter with a pore size of approximately 0.2 micron can filter bacteria from a water solution.
In microfiltration of milk, the problem is that most of the fat globules and some of the proteins are as large as, or larger than, the bacteria. This results in the filter fouling very quickly when membranes with such a small pore size are chosen. It is thus the skim milk phase that passes through the filter, while the cream needed for standardization of the fat content is sterilized, typically together with the bacteria concentrate obtained by simultaneous microfiltration. The principle of microfiltration is discussed in Chapter 6.4, Membrane filters.
In practice, membranes with a pore size of 1.4 micron are chosen to lower the concentration of protein. In addition, the protein forms a dynamic membrane that contributes to the retention of microorganisms.
The microfiltration concept includes an indirect sterilization unit for combined sterilization of an adequate volume of cream for fat standardization and of retentate from the filtration unit.
Figure 14.6 shows a milk treatment plant with microfiltration. The microfiltration plant is provided with two loops working in parallel. Each loop can handle up to 5.000 l/h of skim milk, which means that this plant has a throughput capacity of approximately 10.000 l/h. Capacity can thus be increased by adding loops.
The raw milk entering the plant is pre-heated to a suitable separation temperature, typically about 60 – 63 °C, at which it is separated into skim milk and cream. A pre-set amount of cream, enough to obtain the desired fat content in the cheese milk, is routed by a standardization device to the sterilization plant.
In the meantime, the skim milk is piped to a separate cooling section in the sterilizing plant to be cooled to 50 °C, the normal microfiltration temperature, before entering the filtration plant.
The flow of milk is divided into two equal flows, each of which enters a loop where it is fractionated into a bacteria-rich concentrate (retentate), comprising about 5 % of the flow, and a bacteria-reduced phase (permeate).
The retentates from both loops are then united and mixed with the cream intended for standardization before entering the sterilizer. Following sterilization at 120 – 130 °C for a few seconds, the mixture is cooled to about 70 °C before being remixed with the permeate. Subsequently, the total flow is pasteurized at 70 – 72 °C for about 15 seconds and cooled to renneting temperature, typically 30 °C.
Due to its high bacteria-reducing efficiency, microfiltration allows production of hard and semi-hard cheese without requiring chemicals to inhibit growth of Clostridia spores.
Types of cheese are often classified according to a fat in dry solids basis, FDS. The fat content of the cheese milk must therefore be adjusted accordingly. The protein content of the cheese milk can in some cases also be standardized. For this reason, the protein and fat contents of the raw milk should be measured throughout the year and the ratio between them standardized to the required value. Figure 14.7 shows an example of how the fat and protein content of milk can vary over a year (the figures are a five-year average).
The final fat, protein and dry solids ratios are important factors in the yield and quality of the cheese.
Standardization of fat can be accomplished either by in-line remixing after the separator (see Chapter 6.2, Automatic in-line standardization systems), or, for example, by mixing whole milk and skim milk in tanks followed by pasteurization. The fat content must finally be adjusted to the protein content (or even better to the Casein content) in order to achieve the desired fat in dry solids ratio.
The protein level of the milk can be adjusted by membrane filtration techniques or by adding skim milk powder. The protein content can be levelled up to a constant value corresponding to the maximum level of the year.
When the protein content is increased by ultrafiltration, the level of total dry solids in the milk increases. This affects the cheesemaking process, and ultimately the quality of the cheese. It is also possible to standardize the casein fraction, not just the total protein content.
Additives in cheese milk
The essential additives in the cheesemaking process are the starter culture and the rennet. Under certain conditions it may also be necessary to supply other components such as calcium chloride (CaCl2) and saltpetre (KNO3 or NaNO3). An enzyme, Lysozyme, has also been introduced as a substitute for saltpetre to inhibit Clostridia organisms.
The starter culture is a very important factor in cheesemaking; it performs several duties.
Three principal types of culture are used in cheesemaking:
- Mesophilic cultures with a temperature optimum between 25 and 40 °C
- Thermophilic cultures, which develop at up to 50 °C
- Adjunct cultures. These are added for creating specific taste or texture. In many cases, it is the enzymes created by these bacteria giving these properties.
The most frequently used cultures are mixed strain cultures, containing two or more strains of bacteria, which can support each other in their functioning. Mixed strain cultures often consist of either a cocktail of mesophilic bacteria or thermophilic bacteria, or sometimes a combination of both. These cultures not only produce lactic acid, but also have the ability to form gas (CO2) and aroma components. Carbon dioxide is essential for creating the holes in round-eyed cheeses and supports the openness of granular types of cheese. Gouda, Manchego and Tilsiter are based on mesophilic cultures, and Emmenthal and Gruyère on thermophilic cultures.
Single-strain cultures are mainly used where the object is to develop acid and contribute to protein degradation, e.g. in Cheddar and related types of cheese.
Three characteristic abilities of starter cultures are of primary importance in cheesemaking:
- Produce lactic acid
- Break down the protein and, when applicable
- Produce carbon dioxide (CO2)
The main task of the culture is to develop acid in the curd.
When milk coagulates, bacteria cells are concentrated in the coagulum. Formation of acid lowers the pH, which is important in assisting syneresis (contraction of the coagulum accompanied by expelling of whey). Furthermore, salts of calcium and phosphorus are released, which influence the consistency of the cheese and help to increase the firmness of the curd.
Another important function performed by the acid-producing bacteria is to suppress surviving bacteria from pasteurization or recontamination bacteria, which either need lactose or cannot tolerate lactic acid.
Production of lactic acid stops when all the lactose in the cheese (except in soft cheeses) has been fermented. Lactic acid fermentation is normally a relatively fast process. For some types of cheese, such as Cheddar, it must be completed before the cheese is pressed, and for other types within a week.
If the starter also contains CO2-forming bacteria, acidification of the curd is accompanied by production of carbon dioxide through the action of citric acid fermenting bacteria. Hetero fermentative bacteria in a mixed strain starter culture have the ability to develop CO2 and are essential for production of cheese with a texture of round holes/eyes or irregularly shaped eyes. The evolved gas is initially dissolved in the moisture phase of the cheese; when the solution becomes saturated, the gas is released and creates the eyes.
The ripening process in hard and certain semi-hard cheeses is a combined proteolytic effect in which the original enzymes of the milk and those of the bacteria in the culture, together with rennet enzyme, cause the breakdown of the protein into peptides and amino acids.
Disturbances in cultures
Disturbances in the form of slow acidification or failure to produce lactic acid can sometimes occur.
One of the most common causes is the presence of antibiotics used to cure udder diseases.
Another possible source is the presence of bacteriophages, thermo-tolerant viruses found in the air and soil.
The detrimental action of both phenomena is discussed in Chapter 10, Cultures and starter manufacture.
A third cause of disturbance is detergents and sterilizing agents used in the dairy. Carelessness, especially in the use of sanitizers, is a frequent cause of culture disturbances.
- Detergent residues
CALCIUM CHLORIDE (CaCl2)
A low concentration of Ca ions in the cheese milk causes a soft coagulum. This results in heavy losses of fines (casein) and fat, as well as poor syneresis during cheesemaking.
Between 5 – 20 g of calcium chloride per 100 kg of milk is normally enough to achieve a constant coagulation time and result in sufficient firmness of the coagulum. By adding more CaCl2 the amount of rennet used can be reduced, as the CaCl2 supports the action of rennet. However, excessive addition of calcium chloride may make the coagulum so hard that it is difficult to cut.
For production of low-fat cheese, and if legally permitted, disodium phosphate (Na2PO4), usually 10 – 20 g/kg, can sometimes be added to the milk before addition of calcium chloride. This increases the elasticity of the coagulum due to formation of colloidal calcium phosphate, Ca3(PO4)2, which will have almost the same effect as the milk fat globules trapped in the curd.
Carbon dioxide (CO2)
Addition of CO2 is a method of improving the quality of cheese milk, as the carbon dioxide acts as an inhibitor. Carbon dioxide occurs naturally in milk, but most of it is lost in the course of processing. Adding carbon dioxide by artificial means lowers the pH of the milk. This will then result in shorter coagulation time and a reduction of the amount of rennet.
SALTPETRE (NaNO3 or KNO3)
As previously mentioned, fermentation problems may be experienced if the cheese milk contains spores of butyric-acid bacteria (Clostridia) and/or Coliform bacteria. If bactofugation or microfiltration is not applied, saltpetre (sodium or potassium nitrate) can be used to mask undesired gas forming. However, in recent times more and more saltpetre is being banned from production. Whey containing saltpetre spores are not suitable for infant formula usage.
The colour of cheese is to a great extent determined by the colour of the milk fat, and undergoes seasonal variations. Colours such as carotene and orleana, an anatto dye, are used to correct these seasonal variations in countries where colouring is permitted.
Green chlorophyll (contrast dye) is also used, for example in blue-veined and Feta cheeses, to obtain a “pale” colour as a contrast to the blue mould.
Except for fresh cheese types such as cottage cheese and quarg, in which the milk is clotted mainly by lactic acid, all cheese manufacture depends upon formation of curd by the action of rennet or similar enzymes.
Coagulation of casein is the fundamental process in cheesemaking. It is generally done with rennet, but other proteolytic enzymes can be used, as well as acidification of the casein to the iso-electric point (pH 4.6 – 4.7).
The active principle in rennet is an enzyme called chymosin, and coagulation takes place shortly after the rennet is added to the milk. The renneting process operates in several stages; it is customary to distinguish these as follows:
- Transformation of casein to paracasein under the influence of rennet
- Precipitation of paracasein in the presence of calcium ions
The whole process is governed by the temperature, acidity, and calcium content of the milk, as well as other factors. The optimum temperature for rennet is in the region of 40 °C, but lower temperatures are normally used in practice, principally to enable control of the coagulum’s hardness.
Rennet is extracted from the stomachs of young calves and marketed in the form of a solution with a strength of 1:10.000 to 1:15.000, which means that one part of rennet can coagulate 10.000 – 15.000 parts of milk in 40 minutes at 35 °C. Bovine and porcine rennet are also used, often in combination with calf rennet (50:50, 30:70, etc.). Rennet in powder form is normally 10 times as strong as liquid rennet.
Substitutes for animal rennet
The search for substitutes for animal rennet was carried out primarily in India and Israel, on account of vegetarians’ refusal to accept cheese made with animal rennet. In the Muslim world, the use of porcine rennet is out of the question, which is a further important reason to find adequate substitutes. Interest in substitute products has grown more widespread in recent years due to a shortage of animal rennet of good quality.
There are two main types of substitute coagulants:
- Coagulating enzymes from plants
- Coagulating enzymes from microorganisms
Investigations have shown that coagulation ability is generally good with preparations made from plant enzymes. A disadvantage is that the cheese very often develops a bitter taste during storage.
Various types of bacteria and moulds have been investigated, and the coagulation enzymes produced are known under various trade names.
DNA technology has been utilized in recent times, and a DNA rennet with characteristics identical to those of calf rennet is now being thoroughly tested with a view to securing approval.
Other enzymatic systems
Several research institutions are working to isolate enzymatic systems that can be used to accelerate the ageing of cheese. The technique is not yet fully developed, and is therefore not commonly used.
Cheese of various types is produced in several stages according to principles that have been worked out by years of experimentation. Each type of cheese has its specific production formula, often with a local touch.
Some basic processing alternatives are described below.
Fat, % 3.4
Protein, % 3.3
Lactose, % 4.7
Total solids, % 12.5
As discussed above, the milk intended for most types of cheese is preferably pasteurized just before being pumped into the cheese tank. Milk intended for traditional Swiss Emmenthal cheese or Parmesan cheese is an exception to this rule.
Milk intended for cheese is not normally homogenized, unless it is recombined. The basic reason is that homogenization causes a substantial increase in water-binding ability, making it very difficult to produce semi-hard and hard types of cheese. The losses of fat and dry solids in the whey will also increase.
However, in the special case of blue and Feta cheeses made from cows’ milk, the fat is homogenized in the form of 15 – 20 % cream. This is done to make the product whiter and, more importantly, to make the milk fat more accessible to the lipolytic activity by which free fatty acids are formed; these are important ingredients in the flavour of these two types of cheese.
In all cheesemaking, air pickup should be avoided when the milk is fed into the cheesemaking tank, because this would affect the quality of the coagulum and be likely to cause losses of fat and casein in the whey.
The milk is therefore preferably fed to the tank via a combined bottom inlet/outlet pipe or a foam repressing top inlet.
The starter is normally added to the milk at renneting temperature, while the cheese tank is being filled. There are two reasons for early in-line dosage of starter:
- To achieve good and uniform distribution of the bacteria
- To give the bacteria time to become “acclimatized” to the “new” medium
The time needed from inoculation to start of growth, also called the pre-ripening time, is about 30 to 60 minutes, special in case of adding deep-frozen starter.
The quantity of starter needed varies with the type of cheese. Further information about various starters can be found in Chapter 10, Cultures and starter manufacture.
Additives and renneting
If necessary, calcium chloride and saltpetre are added before the rennet. Anhydrous calcium chloride salt can be used in dosages of up to 20 g/100 kg of milk. Saltpetre dosage must not exceed 30 g/100 kg of milk. In some countries, dosages are limited or prohibited by law.
The rennet dosage is up to 30 ml of liquid rennet of a strength of 1:10.000 to 1:15.000 per 100 kg of milk. To facilitate distribution, the rennet may be diluted with at least double the amount of water. After rennet dosage, the milk is stirred carefully for not more than 5 minutes. It is important that the milk comes to a standstill within another 5 – 8 minutes in order to avoid disturbing the coagulation process and causing loss of casein in the whey.
To further facilitate rennet distribution, automatic dosage systems are available to dilute the rennet with an adequate amount of water and sprinkle it over the surface of the milk through separate nozzles.
Cutting the coagulum
The renneting or coagulation time is typically about 30 minutes. Before the coagulum is cut, a simple test is normally carried out to establish its whey-eliminating quality. Typically, a knife is stuck into the clotted milk surface and then drawn slowly upwards until proper breaking occurs. The curd may be considered ready for cutting as soon as a glass-like splitting flaw can be observed. Equipment for measurement of the progress of the coagulation is available on the market. The principle is the changing in light shattering and reflection. Based on experiences, the cutting point of the set can be started on a fixed output of the measurement.
Cutting gently breaks the curd up into grains with a size of 3 – 15 mm, depending on the type of cheese. The finer the cut, the lower the moisture content in the resulting cheese.
The cutting tools can be designed in different ways. In a modern, enclosed, horizontal cheesemaking tank, Figure 14.8, stirring and cutting are done with tools welded to a horizontal shaft powered by a drive unit with a frequency converter. The dual-purpose tools cut or stir depending on the direction of rotation; the coagulum is cut by razor-sharp radial stainless steel knives. Stirring blades mounted on the tip-ends of the tools, in combination with the rounded backside of the knives, give gentle and effective mixing of the curd.
In addition, the cheese tank can be provided with an automatically operated whey strainer, nozzles for proper distribution of coagulant (rennet) and spray nozzles to be connected to a cleaning-in-place (CIP) system.
Immediately after cutting, the curd grains are very sensitive to mechanical treatment, therefore the stirring has to be gentle. It must, however, be fast enough to keep the grains suspended in the whey. Sedimentation of curd in the bottom of the tank causes formation of lumps. This puts strain on the stirring mechanism, which must be very strong. The curd of low-fat cheese has a strong tendency to sink to the bottom of the tank, which means that the stirring must be more intense than for curd with a high-fat content.
Lumps may influence the texture of the cheese, as well as causing loss of casein in the whey.
The mechanical treatment of the curd and the continued production of lactic acid by bacteria help to expel whey from the grains.
First drainage of whey
For semi-hard types of cheese, such as Gouda and Edam, it is desirable to rid the grains of relatively large quantities of whey, so that heat can be supplied by direct addition of hot water to the mixture of curd and whey, which also lowers the lactose content.
Discharge of whey also makes space for the added water. Some producers also drain off whey to reduce the energy consumption needed for indirect heating of the curd. For each individual type of cheese, it is important that the same amount of whey, normally 30 % of the batch volume, is drained off every time.
Figure 14.8 shows the whey drainage system in an enclosed, fully mechanized cheese tank. A longitudinal slotted tubular strainer is suspended from a stainless steel cable connected to an outside hoist drive. The latest curdmaking vats are equipped with a pneumatic servo cylinder for the upwards and downwards movement of the strainer.
The strainer is connected to the whey suction pipe via a swivel union and then through the tank wall to the external suction connection. A level electrode attached to the strainer controls the hoist motor, keeping the strainer just below the liquid level throughout the whey drainage period. A signal to start is given automatically. A predetermined quantity of whey can be drawn off, which is controlled via a pulse indicator from the hoist motor. Safety switches indicate the upper and lower positions of the strainer.
The whey should always be drawn off at a high capacity, say within 5 – 6 minutes, as stirring is normally stopped while drainage is in progress and lumps may be formed in the meantime. Drainage of whey therefore takes place at intervals, normally during the second part of the pre-stirring period and after heating.
A less sophisticated manner to get rid of the whey is the “hole-in-the-wall” solution. This means that holes are positioned on the tank end walls at fixed levels. This is a cheap way of draining the whey, but has some disadvantages. Whey can only be discharged to fixed levels and the losses of fines in the whey are higher compared to a hoisted whey strainer.
Heat treatment is required during cheesemaking to regulate the size and acidification of the curd. The growth of acid-producing bacteria is limited by heat, which is thus used to regulate production of lactic acid. Apart from the bacteriological effect, the heat also promotes contraction of the curd accompanied by expulsion of whey (syneresis).
Depending on the type of cheese, heating can be done in the following ways:
- By hot water (or saturated steam) in the tank jacket only
- By steam in the jacket in combination with addition of hot water to the curd/whey mixture
- By hot water addition to the curd/whey mixture only
The time and temperature program for heating is determined by the method of heating and the type of cheese. Heating to temperatures above 40 °C, sometimes also called cooking, normally takes place in two stages. At 37 – 38 °C, the activity of the mesophilic lactic acid bacteria is retarded, and heating is interrupted to check the acidity, after which heating continues to the desired final temperature. Above 44 °C, the mesophilic bacteria are totally deactivated, and they are killed if held at 52 °C between 10 and 20 minutes.
Cheddar cheese is cooked by steam in the jacket. The heating slope is normally 0.2 – 0.5 °C/min. Heating beyond 44 °C is typically called scalding. Some types of cheese, such as Emmenthal, Gruyère, Parmesan and Grana, are scalded at temperatures as high as 50 – 56 °C. Only the most heat-resistant lactic-acid-producing bacteria survive this treatment. One that does so is Propionibacterium freudenreichii ssp. shermanii, which is very important to the formation of the character of Emmenthal cheese.
The sensitivity of the curd grains decreases as heating and stirring proceed. More whey is exuded from the grains during the final stirring period, primarily due to the continuous development of lactic acid, as well as the mechanical effect of stirring.
The duration of final stirring depends on the desired acidity and moisture content of the cheese.
Second drainage of whey
In many cheesemaking recipes, a second removal of whey is recommended, as it reduces the required drainage capacity of downstream equipment. This whey can be used for pre-filling of downstream pre-pressing vats or it can be used as start-up fluid for Casomatic systems. This amount of whey from the first removal can be reduced in order to obtain a better whey quality with less fines.
Final removal of whey and principles
of curd handling
As soon as the required acidity and firmness of the curd have been attained – and checked by the producer – most of the residual whey has to be removed from the curd. The already discharged whey is used for pre-fill of the pre-press vat or the drainage column. When continuous drainage equipment is utilized, the whey can be used to achieve the right curd/whey ratio.
The whey, when in the curd/whey mixture, is present in three forms:
- Whey between the curd particles – free whey
- Whey incorporated in the curd grains
- Whey bound to protein
The free whey is easily drainable by increasing the compactness of the curd block by pressing.
The whey inside the grains is more difficult to evacuate. However, by increasing the acidity and applying pressure on the grains, this whey is released and behaves as free whey.
The whey bound to protein is not drainable under normal cheesemaking procedures.
It is vital to the drainage process that the discharge of whey is gentle and does not exert excessive force on the curd. During whey drainage, the curd grains deform and partly fuse together due to the static pressure in the column or the pre-press vat.
Depending on how the curd grains are treated after whey separation, four different types of cheese are obtained.
- If the grains are separated first from the whey, filled in moulds and then turned and/or pressed, the result is a cheese with an open or granular structure, i.e. Tilsiter
- Collecting the grains in a layer for an acidification period results in a cheese with a closed texture, i.e. Cheddar, Mozzarella
- When the curd grains are washed with water and cooled, and then mixed with cream or dressing, the final product will be a type of Cottage cheese
- When the curd is kept under the surface of the whey during thecombined draining and pre-pressing sequence, the result will be a round-eyed type of cheese, i.e. Emmenthal, Gouda
Related properties, essential for cheese quality, are to be controlled via the following parameters of the curd before production continues:
- Moisture content
- Fat content
- Curd grain size and size distribution
- Curd strength and deformability
Cheese with granular texture
The curd/whey mixture is pumped across a static screen, a vibrating strainer or a rotating strainer. The grains are separated from the whey and discharged directly into the pre-pressing vat or column. The resulting cheese acquires a texture with irregular holes or eyes, also called a granular texture, Figure 14.10.
As the curd grains are exposed to air before being collected and pressed, they do not fuse completely; a large number of tiny air pockets remain in the interior of the cheese. The carbon dioxide formed and released during the ripening period fills and gradually enlarges these pockets.
Gas-producing bacteria (Sc. cremoris/lactis, L. cremoris and Sc. diacetylactis) are used in production of round-eyed cheese, Figure 14.11. The Propionic bacteria is responsible for the big eyes in Emmenthal cheese.
Studies of the formation of round holes/eyes have shown that when curd grains are collected below the surface of the whey, the curd contains microscopic cavities. Starter bacteria accumulate in these tiny whey-filled cavities. The gas formed when they start growing initially dissolves in the liquid, but as bacterial growth continues, local supersaturation occurs, which results in the formation of small holes. Later, after gas production has stopped due to lack of substrate, (e.g. citric acid), diffusion becomes the most important process. This enlarges some of the holes, which are already relatively large, while the smallest holes disappear. Enlargement of bigger holes at the expense of the smaller ones is a consequence of the laws of surface tension, which state that it takes less gas pressure to enlarge a large hole than a small one. The course of events is illustrated in Figure 14.12. At the same time, some CO2 escapes from the cheese.
Two systems can be applied for draining the whey under its surface: the horizontal in a pre-pressing vat or vertical in a perforated drainage column (Casomatic system).
The choice of system depends on:
- Type of cheese to be produced
- Batch or continuous production
- Plant production capacity
- Flexibility regarding cheese types and dimensions
- Addition of herbs, spices, etc. in the cheese
- Level of automation
- Level of investment
As part of the cheese production line, there are generally two methods of draining the whey from the curd; separating the whey from the curd grains by a strainer, or settling the curd in the whey before it is decanted. The first method creates a granular curd, while the second produces a round-eyed type of cheese.
Continuous drainage system
The continuous drainage, forming and mould-filling machine offers an advanced drainage system. The Tetra Tebel Casomatic single-column version is shown in Figure 14.14. There is also a multi-column version available in which a changeable insert is placed. This insert contains one to sixteen drainage columns.
Two buffer tanks are also required in the automatic and continuous system. One buffer tank is filled up and the other is emptying. To start with a filled buffer tank ensures a better whey/curd ratio during the whole batch. There is a better batch separation when using two tanks and the stirring action in the buffer tank can be used as a part of the final stirring in the curdmaking process.
The capacity per single column is 1.000 – 1.300 kg/h depending on cheese type. Several columns are usually placed in a row and work parallel filling moulds on a filling conveyor.
In the multi-column version, the capacity depends on cheese type, cheese size and number of drainage tubes in the insert. For semi-hard, round-eyed cheese, the capacity can be 1.000 – 3.000 kg/h.
The buffer tank is a vertical stainless steel tank with a conical bottom. The conical bottom is equipped with a dimple jacket for cooling. Inside the tank, a stirrer is situated in the lower conical part. The stirrer speed is adjustable in correlation with the filling height of the tank, as the intensity of stirring is critical for the curd/whey ratio.
The buffer tank in the drainage system is intended to:
- Create a uniform feed of curd/whey mixture
- Be a link between batch curd production and continuous drainage
- Cool the curd/whey mixture for moisture accuracy control of the final cheese
- Deaerate the curd/whey mixture
- Extend the stirring period and release the cheesemaking tank for a new batch
- Mix the curd with other ingredients, i.e. herbs, spices
The curd/whey mixture, normally in a ratio of 1:3.5 – 5.0, is pumped from the buffer tank to the drainage columns by a frequency-controlled positive displacement pump.
In the single-column system, the curd/whey mixture enters the column under the whey level for round-eyed cheese production. A hopper located on top of each column assures a more or less constant whey level during production. The column is filled up with curd, but the whey level is always above the level of curd to avoid incorporation of air in the curd.
The drainage columns can be round or rectangular-shaped to suit the cheese to be produced. The cheese size depends on the type of cheese, the drainability of the whey and the capacity.
A pre-drainage screen can be placed on the top of the column if granular types of cheese are to be produced. The hopper on top of the column contains two level control systems (whey and curd) and a pressure indicator. An overflow gauge assures that the level in the column is always constant.
The whey is drained off in three perforated sections at different levels of the column. For draining, the driving force is the pressure difference between the curd/whey mixture inside the column and the whey on the outside. The pressure difference is set as a recipe parameter in the processing control computer software. Each of the three perforated sections has its own specific pressure difference, controlled by remote regulating valves. As the curd column becomes more compact, the more the pressure difference can increase. The resulting effect is that when the curd column descends, a greater pressure difference is allowed and more whey can be drained.
The moisture accuracy at the bottom of the curd column will be high and, as the dosing height is pre-set, the final cheese weight is accurate.
The column of curd rests on a horizontal knife. At pre-set intervals, the curd column is cut in uniform blocks and placed in moulds. The operating sequence is:
- A slide cassette is positioned under the column and a support dosing plate is pushed up through the slide cassette until it is just underneath the knife
- The knife opens and the curd column rests on the dosing plate. This descends to the pre-set height for the cheese block
- The knife cuts off the curd column and the bottom of the column closes
- The dosing plate descends to its bottom position
- The slide cassette with the curd block is pushed forward to a horizontal sluice
- The sluice gate opens and the curd block falls into a mould
- The slide cassette is positioned back under the column, the sluice gate locks, and the dosing plate is again pushed up and ready for the next dosing and mould-filling sequence
The Tetra Tebel Casomatic multi-column system is a vertical unit that provides higher production flexibility in terms of cheese sizes and shapes. The inner drainage insert can be replaced by other inserts containing inner drainage tubes of various configurations and dimensions. The drainage insert can consist of one single tube, round or rectangular, i.e. one Euroblock 295 x 495 mm, or 16 small tubes, i.e. for baby Gouda.
The drainage inserts are hoisted and placed on a platform adjacent to the column when changed. Two or more columns are normally placed beside each other using the same mould conveyor for delivering cheeses. The moulds used must all have the same outer measurements. When inserts with several drainage tubes are used, multi-moulds with the same configuration as the insert tube must be used.
The curd/whey mixture is pumped from the buffer tanks to the top of the multi-column. The inlet is tangential and a rotating distributor ensures uniform filling of each drainage tube. The whey level is always above the curd level when producing round-eyed cheeses.
When granular cheese is to be produced, a pre-drainage screen is placed on top of the column.
The discharge of whey through three perforated sections is equal to that of the single-column system.
Both versions of the continuous drainage and mould-filling systems are designed and equipped for CIP cleaning.
The whey is drained off in the batch-operated pre-pressing vat, and the curd is pre-pressed before being portioned and moulded.
Pre-pressing vats are available for different batch sizes from 7,000 up to 20,000 l. The inside height of the vat is about 450 mm.
The pre-pressing vat consists of a stainless steel, rectangular open vat with double walls. In the front part of the vat is a door, which can be closed when the vat is filled. The end walls are covered with perforated screens for whey drainage. Their positions are not fixed and can be set depending on the type of cheese, curd amount, curd layer thickness, etc.
The bottom of the vat is covered by a plastic, woven belt that can move forwards or backwards. Whey is drained through the belt, which supports the curd layer. The plastic belt also transports the curd bed out of the vat after drainage.
Whey from the cheesemaking tank is pumped to the pre-pressing vat to prevent incorporation of air into the curd and warm up the cold stainless steel vat.
The curd/whey mixture is then automatically spread into a uniform layer by a movable distributor, which runs on the sidewall of the vat. In the case of granular cheese production, the curd is distributed in the same way, but the whey is first strained off and collected in a tank.
Curd/whey can also be filled through different pipe outlets above the vat. The operator then has to manually rake the curd to a uniform layer before pre-pressing is applied.
An overall, pneumatically-operated, pressing plate hangs in a frame over the curd bed and covers the whole layer. The pressing plate is perforated for whey drainage. Maximum pressure on the curd is around 50 g/cm2.
After the pressing is completed, the discharge end of the vat is opened and the plastic belt moves the complete curd block a pre-set distance. A guillotine knife cuts off a slab of curd. This slab is transported sideways and another guillotine knife cuts off a pre-set length, so that it fits in the mould for final pressing. These operations continue until the vat is empty. Alternatively, fixed vertical ribbon knives can be mounted at the end for longitudinal cutting of the curd bed. Mould filling can be manual or mechanized.
A modern pre-press vat is normally designed and equipped for CIP cleaning.
The curd blocks leaving the drainage equipment are placed in a mould for final pressing. The shape of the mould should correspond with the shape of the final cheese.
After the curd block is placed in the mould, a lid is placed on top of the curd block. The lid must fit the mould opening exactly in order to minimize uneven rims. The filled mould is conveyed to the pressing section of the plant.
The moulds are used to:
- Get rid of most of the remaining whey in the curd block
- Form a stable rind on the cheese surface
- Achieve the correct, uniform shape of the cheese
The mould and lid are either perforated or the inside is fitted with a net. The net can be free-hanging or incorporated in the mould. On micro-perforated moulds, grooves on the inside contribute to good rind forming and drainage.
Most of the cheese moulds are made from plastic, but in some plants stainless steel moulds are still in use. Their design must be very rigid to withstand the applied pressure, conveying and mechanized handling. Each mould and lid is in use several times during a production run. They must also withstand common cleaning detergents as they pass a cleaning station in their production loop.
Closed texture cheese
Closed texture types of cheese, of which Cheddar is a typical example, are normally made with starter cultures containing bacteria that do not produce gas – typically single-strain, lactic-acid-producing bacteria like S. cremonis and S. lactis.
The specific processing technique may, however, result in formation of cavities called mechanical holes, as shown in Figure 14.20. While the holes in granular and round-eyed cheeses have a characteristically shiny appearance, mechanical holes have rough inner surfaces.
When the pH of the curd mass has reached about 6.0 – 6.1 (about two hours after renneting), the whey is drained off, and the curd is subjected to a special form of treatment called cheddaring.
After all whey has been discharged, the curd is left for continued acidification and matting. During this period, typically 2 – 2.5 hours, the curd is formed into blocks, which are turned upside down and stacked. When the pH of the cheddared curd has reached 5.20 – 5.25, the blocks are milled into “chips”, which are dry-salted before being hooped (moulds for Cheddar cheese are called hoops).
Mechanized cheddaring machine
A highly advanced, mechanized cheddaring machine, the Tetra Tebel Alfomatic, is also available, and the principle is shown in Figure 14.21. These machines have capacities ranging from one to eight tonnes of cheese per hour. The most common version of the machine is equipped with four conveyors, individually driven at pre-set and adjustable speeds, and mounted above each other in a stainless steel frame. The curd/whey mixture is uniformly distributed on a special drainage screen, where most of the whey is removed. The curd then falls on to the first conveyor, which is perforated and has stirrers for further whey drainage. Guide rails control the width of the curd mat on each conveyor.
The second conveyor allows the curd to begin matting and fusing. It is then transferred to a third conveyor, where the mat is inverted and cheddaring takes place.
At the end of the third conveyor, the curd is milled to chips of uniform size, which fall onto the fourth conveyor. In machines for stirred curd types (Colby cheese), additional stirrers can be added on conveyors 2 and 3 to facilitate constant agitation, preventing fusing of the curd granules. In this case, the chip mill is also bypassed.
The last conveyor is the mellowing conveyor. Salt is added to the curd at the beginning and left on, so that it can diffuse into the curd. The curd is stirred during its mellowing time to prevent it from fusing, and to promote even absorption of the salt.
An alternative system for salt application is the salt mixing drum system as shown in Figure 14.21. After the chip mill, the curd is weighed and salt is added accordingly (on a weight-for-weight basis). The salt and curd enter a flighted mixing drum, which provides efficient mixing. The salted curd will then enter the last conveyor for its mellowing period.
The first conveyor can also be equipped with a wash-water system for production of the aforementioned Colby cheese.
A machine with two or three conveyors suffices for production of cheeses of the Pasta Filata family (Mozzarella, Kashkaval, Pizza cheese, etc.), in which cheddaring is a part of the processing technique, but the milled chips are not normally salted before cooking and stretching.
The machine, regardless of the number of conveyors, is equipped with spray nozzles for connection to a CIP system to ensure thorough cleaning and sanitation.
Final treatment of curd
As previously mentioned, the curd can be treated in various ways after most of the free whey has been removed. It can be:
- Transferred directly to moulds (granular cheeses)
- Pre-pressed into a block and cut into pieces of suitable size for placing in moulds (round-eyed cheeses)
- Sent to cheddaring, the last phase of which includes milling into chips, which can be dry-salted and either hooped or shaped under vacuum, if intended for Pasta Filata types of cheese, transferred unsalted to a cooking-stretching machine
After having been moulded or hooped, the curd is subjected to final pressing. There are five aims to:
- Assist final whey expulsion
- Provide texture
- Reach desired acidification
- Shape the cheese
- Provide a rind on cheeses with long ripening periods
The rate of pressing and pressure applied are adapted to each particular type of cheese. Pressing should be gradual at first, because initial high pressure compresses the surface layer and can lock moisture into pockets in the body of the cheese.
The pressure applied to the cheese should be calculated per unit area and not per cheese, as individual cheeses may vary in size, e.g. 300 g/cm2.
The pressure used depends on:
- Cheese dimensions
- Curd temperature
- Fat content
- Acidity level
- Type of mould
- Amount of residual whey in the cheese
- Available time for pressing
Most cheese presses are single presses, except for cheddar, in which case moulds are stacked. The pressure, hydraulic or pneumatic, is supplied to a pressing cylinder – one for each mould. The cheeses can be pressed per batch or per row in cases where a conveyor press is used.
The trend is to go for closed presses. The advantages are a better control over the ambient temperature and a total CIP cleanable press.
Pressing systems are available in open and close execution. Closed presses are applied in high capacity lines with a focus on hygiene and limited process variations. Open presses are normally applied in low-capacity and low-cost lines.
Recently producers with strong focus on whey quality and efficiency can choose for a new pressing system what's introduced; the container press system.
Arriving on a conveyor system, the filled moulds are automatically pushing device. The rows of moulds in the press are transported by push bars/side guidings and slide across a stainless steel floor.
When the press has been filled, the curd blocks will be pressed. The pressure and intervals between increases of pressure, as well as the total pressing time, are automatically controlled. A press system is designed for simultaneous loading and unloading, which allows optimum utilization of the press. Downstream the presses the curd blocks are demoulded and transported to the brining system. Moulds and lids are cleaned in a washing machine and transported back to the mould filling area.
The container press systems works according to the same principles as described above. The only difference is that moulds after filling are positioned in containers. During pressing the pressing whey is collected in the container instead of on the pressing floor. After each pressing cycle containers are emptied and cleaned ensuring first class pressing whey production during a whole production run. It also eliminates the need for cleaning of the presses after each production run.
The blockformer system
Producing well-formed uniform blocks has long been a critical problem for Cheddar cheese producers. The Tetra Tebel Blockformer, utilizing a basically simple system of vacuum treatment and gravity feed, solves this problem. The milled and salted chips are drawn by vacuum to the top of a tower, as illustrated in Figure 14.23. The tower is filled, and the curd begins to fuse into a continuous columnar mass.
Vacuum is applied to the column throughout the program to deliver a uniform product, free from whey and air, at the base of the machine. Regular blocks of identical size, typically weighing about 18 – 20 kg, are automatically cut, ejected, and bagged ready for conveying to the vacuum sealing unit, which is integral with the production line. No subsequent pressing is needed.
Different tower types are available, each offering a different capacity. A standard blockformer tower has a height of some 8 metres. An extended blockformer, with an actual column height of around 7.5 metres, has a capacity of 1.000 kg/h.
A Twinvac blockformer has a capacity of 1.600 kg/h. This blockformer’s column has a height of around 9 metres. The high capacity can be obtained as a result of a split in the vacuum applied to the curd column and the vacuum used for curd transport from the cheddaring machine. A more efficient and longer vacuum will be applied to the curd column, thus increasing the blockformer’s capacity. Two vacuum units are required for the Twinvac blockformer.
CIP manifolds at the top of the towers assure good cleaning and sanitizing results.
Cooking and stretching of Pasta Filata types of cheese
Pasta Filata (plastic curd) cheese is characterized by an “elastic” string curd obtained by cooking and stretching cheddared curd. The “spun curd” cheeses – Provolone, Mozzarella, and Caciocavallo – originate from southern Italy. Nowadays, Pasta Filata cheese is produced not only in Italy, but also in several other countries. The Kashkaval cheese produced in several Eastern European countries is also a type of Pasta Filata cheese. The terms “low-moisture Mozzarella” and “pizza cheese” may be used to describe Pasta Filata cheese products designed to meet the requirements of pizza manufacturers.
After cheddaring and milling, at an acidity of approx. 0.7 – 0.8 % lactic acid in the whey (31 – 35.5 °SH), the chips are conveyed or shovelled into a steel mixing bowl or container, or into a sanitary dough-mixing machine filled with hot water at 65 – 70 °C, and the pieces are processed until they are smooth, elastic, and free from lumps. The mixing water is normally saved and separated with the whey to conserve fat.
Stretching and mixing must be thorough. “Marbling” in the finished product may be associated with incomplete mixing, water temperature that’s too low, low-acidity curd, or a combination of these defects.
Continuous cooking and stretching machines are used in large-scale production. Figure 14.24 shows a Cooker-Stretcher. The speed of the counter-rotating augers is variable, so that an optimal working mode can be achieved. The temperature and level of cooking water are continuously controlled. The cheddared curd is continuously transferred into the hopper or cyclone of the machine, depending on the method of feeding – screw conveyor or blowing.
In production of Kashkaval cheese, the cooker may contain brine with 5 – 6 % salt instead of water. Warm brine, however, is very corrosive, so the container, augers and all other equipment coming into contact with the brine must be made of highly-durable special material.
As Pasta Filata cheese often occurs in various shapes – ball, pear, sausage, etc. – it is difficult to describe the process of moulding. However, automatic moulding machines are available for square or rectangular types, normally pizza cheese. Such a moulder typically comprises counter-rotating augers and a revolving mould-filling system, as illustrated in Figure 14.25.
The plastic curd enters the moulds at a temperature of 55 – 65 °C. To stabilize the shape of the cheese and facilitate emptying the moulds, the moulded cheese must be cooled. To shorten the cooling/hardening period, a hardening tunnel must be incorporated in a complete Pasta Filata line.
A production line for Pasta Filata types of cheese is illustrated in Figure 14.34.
In cheese, as in a great many foods, salt normally functions as a condiment. However, salt has other important effects, such as retarding starter activity and bacterial processes associated with cheese ripening. Application of salt to the curd causes more moisture to be expelled, both through an osmotic effect and a salting effect on the proteins. The osmotic pressure can be likened to the creation of suction on the surface of the curd, causing moisture to be drawn out.
With few exceptions, the salt content of cheese is 0.5 – 2.0 %. Blue cheese and white pickled cheese variants (Feta, Domiati, etc.), however, normally have a salt content of 3 – 7 %.
The exchange of calcium for sodium in paracaseinate that results from salting also has a favourable influence on the consistency of the cheese, which becomes smoother. In general, for semi-hard cheeses, the curd is exposed to salt at a pH of 5.3 – 5.6, i.e. approx. 5 – 6 hours after the addition of a vital starter, provided the milk does not contain bacteria-inhibiting substances.
Dry salting can be done either manually or mechanically. Salt is applied manually from a bucket or similar container containing an adequate (weighed) quantity that is spread as evenly as possible over the curd after all whey has been discharged. For complete distribution, the curd may be stirred for 5 – 10 minutes.
There are various ways to distribute salt over the curd mechanically. One is the same method as that used for salting of cheddar chips during the final stage of passage through a continuous cheddaring machine.
Another is a partial salting system used in production of Pasta Filata cheese (Mozzarella), illustrated in Figure 14.26. The dry salter is installed between the cooker-stretcher and moulder. With this arrangement, the normal brining time of eight hours can be reduced to some two hours, and less area is needed for brining.
Brine salting systems of various designs are available, from fairly simple to technically very advanced. The most commonly used system remains the placing of the cheese in a container with brine. The containers should be placed in a cool room at about 12 – 14 °C.
A variety of systems based on shallow brining or containers for racks are available for large-scale production of brine-salted cheese.
Shallow or surface brining
In a shallow brining system, the cheese is floated into compartments, where brining in one layer takes place. To keep the surface wet, the cheese is dipped below the surface at intervals by a roller on the rim of each compartment. The dipping procedure can be programmed.
Figure 14.28 shows the principle of a shallow brining system.
In a deep brining system, the cheeses float into hoisted cages. A cage consists of a number of perforated layers that are filled one by one with floating cheeses. Normally, the filling starts with the lowest layer. When one layer is filled, the cage descends one layer. The 2.5 – 3.0 m deep cages are mostly dimensioned for a batch covering a certain number of layers.
In general, deep brining is mostly used for longer brining times, due to the differences in brining time from the first to the last input. The system works on a first in-last out basis.
In the case of short brining times, there will be a difference in salt absorption. To achieve a more uniform brining time, the loaded cages can be emptied when half the time has elapsed and the cheeses are directed to an empty cage. The cheeses from the top layer of the first cage fill the bottom layer of the next cage.
Circulation of the brine through the filled cages is essential for refreshment of the brine around the cheeses. Turbines in the floating canals take care of both the transport of cheeses to and from the cages and the brine circulation.
Rack brining system
Another deep brining system is based on racks. These racks are filled with cheeses and the filled racks are placed in a brine bath. The size and loading of a rack predict the maximal variation in brining time. All operations – filling the racks, placing them in the brine solution, hoisting the racks out of the brine and guiding them to an unloading station – can be completely automated. The principle of a rack brining system is shown in Figure 14.29.
Preparation of brine
The difference in osmotic pressure between brine and cheese causes some moisture with its dissolved components, whey proteins, lactic acid and minerals to be expelled from the cheese in exchange for sodium chloride. In the preparation of brine, it is important that this is taken into consideration. The brine has to be tested regularly for composition and temperature.
Salt is normally dissolved in the transport canal. Besides dissolving salt to the desired concentration, the pH should be adjusted, e.g. with edible hydrochloric acid, to 4.6 – 4.8, but always lower than the final pH of the cheese. The hydrochloric acid must be free from heavy metals and arsenic. Lactic acid can of course be used, as can other “harmless” acids.
Calcium in the form of calcium chloride (CaCl2) should also be added to give a calcium content of 0.1 – 0.2 %. Normally, the Ca content of the brine is kept on level by the exchange of Ca and Na.
Table 14.2 can serve as guide for preparation of brine. There is often a brine buffer from which the brine is pumped in case the brine bath is not completely filled up with cheeses. Brine flows back into the buffer when the cages are being filled.
Salt penetration in cheese
The following brief description, based on Report No. 22 from Statens Mejeriforsøg, Hillerød, Denmark, gives an idea of what happens when cheese is salted:
Cheese curd is criss-crossed by capillaries; approximately 10.000 capillaries per cm2 have been found. There are several factors that can affect the permeability of the capillaries and the ability of the salt solution to flow through them, but not all such factors are affected by changes in technique. This applies, for example, to the fat content. As fat globules block the structure, salt penetration will take longer in a cheese with a high fat content than one with a low fat content.
The pH at the time of salting has considerable influence on the rate of salt absorption. More salt can be absorbed at low pH than at higher pH. However, at low pH, (e.g. <5.0), the consistency of the cheese is hard and brittle. At high pH, (e.g. >5.6), the consistency becomes elastic.
The importance of the pH of the cheese at the time of brining has been described by the research team at the Danish Government Research Institute for Dairy Industry in Hillerød:
Some parts of the calcium are more loosely bound to the casein, and at salting, the loosely bound calcium is exchanged for sodium by ion exchange. Depending on the quantity of loosely bound calcium, this determines the consistency of the cheese.
This loosely bound calcium is also sensitive to the presence of hydronium ions (H+). The more H+ ions, the more calcium (Ca++) ions will leave the casein complex, and H+ will take the place of calcium. At salting, H+ is not exchanged for the Na+ (sodium) of the salt. This means:
- At high pH (6.0 – 5.8), there is more calcium in the casein. Consequently, more sodium will be bound to the casein complex, and the cheese will be softer; it may even lose its shape during ripening.
- At pH 5.2 – 5.6 there may be enough Ca++ and H+ ions in the casein complex to bind enough Na+ to the casein. The resulting consistency will be good.
- At low pH (< 5.2), too many H+ ions may be included; as the Na+ ions cannot be exchanged for the H+ ions, the consistency will be hard and brittle.
Conclusion: it is important that cheese has a pH of about 5.4 before being brine salted.
Temperature also influences the rate of salt absorption and thus the loss of moisture. The higher the temperature, the higher the rate of absorption.
The higher the salt concentration of the brine, the more salt will be absorbed. At low salt concentrations, (e.g. <16 %), the casein swells and the surface will be smeary and slimy as a result of the casein being redissolved.
Salt concentrations of up to 18 – 23 % are often used at 10 – 14 °C.
The duration of salting depends on:
- Salt content typical of the type of cheese
- Size of the cheese – the larger it is, the longer it takes
- Salt content and temperature of the brine
In addition to readjusting the concentration of salt, the microbiological status of the brine must be kept under control, as various quality defects may arise. Certain salt-tolerant microorganisms can decompose protein, giving a slimy surface; others can cause formation of pigments and discolour the surface. The risk of microbiological disturbances from the brine is greatest when weak brine solutions, <16 %, are used.
Pasteurization is sometimes employed when the brine volume is limited.
- A hygienic design of the brining system is very important; easy cleaning, no dead corners and no difficult-to-reach spots. It is the foam and fat remains at the border between brine and air that enables bacteria to grow. That has to be cleaned by hand.
- The brining system should then be so designed that pasteurized and unpasteurized brine are not mixed
- Brine is corrosive, so non-corroding heat exchanger materials such as titanium must be used; these materials, however, are expensive
- Pasteurization upsets the salt balance of the brine and causes precipitation of calcium phosphate; some of this will stick to the plates and some will settle to the bottom of the brining container as sludge.
Other ways to reduce or stop microbiological activity are:
- Passing the brine through UV light, provided that the brine has been filtered, and will not be mixed with untreated brine after the treatment
- Microfiltration, which has become the most attractive method for brine purification
Table 14.3 lists the salt percentages in some types of cheese.
Ripening and storage of cheese
After curdling, all cheese, apart from fresh cheese, goes through a whole series of processes of a microbiological, biochemical and physical nature. These changes affect the lactose, protein and fat, and constitute a ripening cycle that varies widely between hard, medium-soft and soft cheeses. Considerable differences occur even within these groups.
The techniques that have been devised for making different kinds of cheese are always directed towards controlling and regulating the growth and activity of lactic acid bacteria. In this way, it is possible to simultaneously influence both the degree and the speed of fermentation of lactose. It has been stated previously that in the cheddaring process, the lactose is already fermented before the curd is hooped. As far as the other kinds of cheese are concerned, lactose fermentation ought to be controlled in such a way that most of the decomposition takes place during the pressing of the cheese and, at the latest, during the first week, or possibly the first two weeks, of storage.
The lactic acid produced is neutralized to a great extent in the cheese by the buffering components of milk, most of which have been included in the coagulum. Lactic acid is thus present in the form of lactates in the completed cheese. At a later stage, the lactates provide a suitable substrate for the propionic acid bacteria, which are important parts of the microbiological flora of Emmenthal, Gruyère and similar types of cheese. Besides propionic acid and acetic acid, a considerable amount of carbon dioxide is produced, which is the direct cause of the formation of the large round eyes in the above-mentioned types of cheese.
The lactates can also be broken down by butyric acid bacteria. If the conditions are otherwise favourable for this fermentation, hydrogen is evolved, in addition to certain volatile fatty acids and carbon dioxide. This faulty fermentation arises at a late stage, and the hydrogen can actually cause the cheese to burst.
The starter cultures normally used in the production of the majority of hard and medium-soft kinds of cheese not only cause the lactose to ferment, but also have the ability to attack the citric acid in the cheese simultaneously. This produces the carbon dioxide that contributes to formation of both round and granular eyes.
Fermentation of lactose is caused by the lactase enzyme present in lactic acid bacteria.
The ripening of cheese, especially hard cheese, is characterized first and foremost by the decomposition of protein. The degree of protein decomposition affects the quality of the cheese to a very considerable extent, most of all its consistency and taste.
The decomposition of protein is brought about by the enzyme systems of:
- Plasmin, an enzyme that is part of the fibrinolytic system
The only effect of rennet is to break down the paracasein molecule into polypeptides. This first attack by the rennet, however, enables a considerably quicker decomposition of the casein through the action of bacterial enzymes than would be the case if these enzymes had to attack the casein molecule directly. In cheese with high cooking temperatures, scalded cheeses like Emmenthal and Parmesan, plasmin activity plays a role in this first attack.
In medium-soft cheeses like Tilsiter and Limburger, two ripening processes proceed parallel to each other, such as the normal ripening process of hard rennet cheese and the ripening process in the smear that is formed on the surface. In the latter process, protein decomposition proceeds further until ammonia is finally produced as a result of the strong proteolytic action of the smear bacteria.
The purpose of storage is to create the external conditions that are necessary to control the ripening cycle of the cheese as far as possible. For every type of cheese, a specific combination of temperature and relative humidity, air circulation and air velocity must be maintained in the different storage rooms during the various stages of ripening.
Different types of cheese require different temperatures and relative humidities (RH) in the storage rooms.
The climatic conditions are of great importance to the rate of ripening, loss of weight, rind formation and development of the surface flora (in Tilsiter, Romadur and others) – in other words to the total nature or characteristics of the cheese.
Cheeses with rinds, most commonly hard and semi-hard types, can be provided with a plastic emulsion, paraffin or wax coating.
Rindless cheese is covered with a plastic film or packed in semi-permeable or shrinkable plastic bag, mostly under vacuum condition.
Covering the cheese has a dual purpose:
- Prevent excessive water loss
- Protect the surface from infection and dirt
The four examples below will give some idea of the variety of storage conditions for different kinds of cheese.
- Cheeses of the Cheddar family are often ripened at low temperatures, 4 – 8 °C, and a RH lower than 80 %, as they are normally wrapped in a plastic film or bag and packed in cartons or wooden cases before being transported to the store. The ripening time may vary from a few months up to 8 – 10 months, to satisfy the preferences of various consumers.
- Other types of cheese like Emmenthal may need to be stored in a “green” cheese room at 8 – 12 °C for some 3 – 4 weeks, followed by storage in a “fermenting” room at 22 – 25 °C for some 6 – 7 weeks. After that, the cheese is stored for several months in a ripening store at 8 – 12 °C. The relative humidity in all rooms is normally 85 – 90 %.
- Smear-treated types of cheese – Tilsiter, Havarti and others – are typically stored in a fermenting room for around two weeks at 14 – 16 °C and a RH of about 90 %, during which time the surface is inoculated with a special cultured smear mixed with a salt solution. Once the desired layer of smear has developed, the cheese is normally transferred to the ripening room at a temperature of 10 – 12 °C and a RH of 90 % for a further 2 – 3 weeks. Eventually, after the smear is washed off and cheese is wrapped in aluminium foil, it is transferred to a cold store (6 – 10 °C and about 70 – 75 % RH), where it remains until distributed.
- Other hard and semi-hard types of cheese, Gouda and similar, may first be stored for a couple of weeks in a “green” cheese room at 10 – 12 °C and a RH of some 75 %. After that, a ripening period of about 3 – 4 weeks may follow at 12 – 18 °C and 75 – 80 % RH. Finally, the cheese is transferred to a storage room at about 10 – 12 °C and a relative humidity of about 75 %, where the final characteristics are developed.
The values given for temperatures and relative humidities, RH, are approximate and vary for different sorts of cheese within the same group. The humidity figures are not relevant to film-wrapped or bag-ripened cheese.
Methods of air conditioning
A complete air conditioning system is normally required to maintain the necessary humidity and temperature conditions in a cheese ripening store, because humidity has to be removed from the cheese, which is difficult if the outside air has a high humidity. The incoming air must be dehumidified by refrigeration, which is followed by controlled rehumidification and heating to the required conditions.
It may also be difficult to distribute air humidity equally to all parts of the storeroom.
Distribution ducts for the air may be of some help, but they are difficult to keep free from mould contamination. The ducts must therefore be designed to allow cleaning and disinfection.
Storage layout and space requirements
The layout depends on the type of cheese. Installing permanent cheese racks in the store has been the conventional solution for both hard and semi-hard cheeses. The capacity of a store for cheeses weighing about 8 – 10 kg, with ten racks above each other is approximately 300 – 350 kg/m2. Gangways between the racks are 0.6 m wide and the main corridor in the middle of the store is usually 1.5 – 1.8 m wide. Mounting the racks on wheels or hanging them from overhead rails eliminates the need for gangways between racks. They can be put close to each other and need only be moved when the cheese is handled. This system increases the capacity of the store by 30 – 40 %, but the cost of the store and building remains at the same level because of the higher cost of this type of rack.
Pallet racks or containers are a widely used system. Pallets or pallet containers can also be put on special wheeled pallets running on rails. This method also permits compact storage. Figure 14.30 shows a mechanized cheese store. A wooden shelf holding five cheeses is conveyed into the green cheese storage and then into a specially designed elevator – not shown in the picture – which lowers or lifts the shelf to a pre-set level and pushes it into storage. Figure 14.31 shows a ripening store based on pallets.
Cheese ripened in film is packed in cardboard boxes and piled on pallets for the later part of the storage period. This means that the cheese can be stored compactly. The pallets cannot be stacked on top of each other, but pallet racks can be used. However, the load per unit area must be taken into consideration if this method is adopted, as the weight will far exceed the normal load allowed in old buildings.
In comparison with permanent racks, the container system increases the storage capacity considerably.
There are companies that specialize in storage systems of various degrees of sophistication; anything from traditional racks up to and including computerized systems. They can also advise about optimum air conditioning for the various systems.
Processing lines for hard and semi-hard cheese
The following part of this chapter will only describe examples of processing lines for typical types of cheeses.
Hard types of cheese
Processing line for Cheddar cheese
Cheddar cheese and similar types are the most widely produced in the world.
Cheddar cheese generally has a moisture on a fat-free basis (MFFB) of 55 %, which means it can be classified as hard cheese, although it is on the verge of semi-hard types. The principle of a highly mechanized production line is shown in Figure 14.32.
The curd is normally manufactured from fat-standardized and pasteurized milk. At a pH of about 6.3, after some 2 to 2.5 hours of curd production, the curd-whey mixture is pumped from the cheese tank into the continuous cheddaring machine (2). Pre-drawing of whey is not normally practised.
To maintain a continuous feed, a calculated number of cheese tanks is scheduled for emptying in sequence at regular intervals, say every 20 minutes.
After a cheddaring period of about 2.5 hours including milling and dry salting of the chips at a curd pH of 5.3, the chips are transported by vacuum to a blockformer (3). An adequate number of blockformers must be available to maintain continuity.
The exit of each blockformer is manually provided with a plastic bag into which the cut-out block is pushed. Also an automatic bag loader can be intergraded in the line. The bagged block is then conveyed to a vacuum sealing machine (4). Following sealing, the cheese is weighed (5) en route to a packing machine (6), where it is covered by a carton, which is then conveyed to a rapid cooling store (7). The cheese is cooled down to a core temperature of approximately 15 °C in about 24 hours at a store temperature of 2 – 3 °C. Finally, the cheese is palletized and held from 4 to 12 months in the ripening store at a temperature of 5 – 10 °C.
Semi-hard types of cheese
Processing line for Gouda cheese
Gouda is probably the best-known representative of typical round-eyed cheeses. A Gouda processing line is illustrated in Figure 14.33.
Fat-standardized pasteurized milk is transformed into curd and whey in the usual manner in about two hours. Normally, part or sometimes all of the heating is done by direct addition of hot (50 – 60 °C) water in an amount equal to 10 – 20 % of the original volume of milk. To make this possible, some 30 – 40 % of whey must first be drained off.
After completion of curd production and further drainage of whey to a curd/whey ratio of 1:3.5 – 5.0, the contents of the cheese tank are emptied into a buffer tank (2) provided with an agitator for proper distribution of the curd in the whey. The tank is also jacketed to enable the curd to be chilled to 1 – 2 °C with cold water and to control the moisture content in the batch.
The whey/curd mixture is pumped from the filled buffer tank into one or more drainage columns (4). At the very start, however, the column is first filled with whey, so that the subsequent curd will not be exposed to air when it enters the column.
For continuous operation, a suitable number of cheese tanks is operated in sequence and emptied at regular intervals of about 20 – 30 minutes.
Following pre-pressing, the cheese block is pushed out of the machine. Normally, the blocks are fed by gravity into clean moulds conveyed from the washing machine and stationed underneath the columns. A fully mechanized system also comprises:
- Mechanical lidding (5) of the moulds
- Transfer of moulds to conveyor or tunnel presses with pre-programmed pressures and pressing times (6)
- Filling and emptying of the presses
- Transport of moulds via a de-lidding station (7), a mould-turning device, a mould-emptying system and a weighing scale (8) to anadvanced brining system (9).
The moulds and lids are separately conveyed to a combined mould and lid washing machine before being re-used.
After brining, the cheese is stored in a green cheese store for about 10 days at 10 – 12 °C, after which storage continues in a ripening store at 12 – 15 °C for some 2 – 12 months.
Processing line for Tilsiter cheese
Tilsiter has been chosen as a representative of granular textured cheese. The principle of a mechanized production line is similar to that for Gouda, but with a few exceptions.
Milk pre-treatment and curd production are similar to those of Gouda cheese. The first basic difference is, that before the curd/whey mixture enters the column, the whey is separated from the curd. This is done in a strainer (4) located on top of the column.
After brining, however, Tilsiter cheese undergoes special treatment involving smearing of the surface with a bacteria culture in a 5 % salt solution to give it its specific flavour. Tilsiter cheese is therefore first stored in a fermenting room with a high relative humidity (90 – 95 %) and a temperature of about 14 – 16 °C. The smearing procedure is either manual or partly mechanized, and the smeared cheese is stored for about 10 – 12 days.
Following the period of surface treatment, the cheese is forwarded to ripening storage at 10 – 12 °C, often after having passed a washing machine. The time in this store is around 2 – 3 weeks.
In conjunction with dispatch from the ripening store, the Tilsiter cheese may be washed and wrapped in aluminium foil before being transferred to a cold store at 6 – 10 °C.
Processing line for Pasta Filata cheese
“Formaggio a pasta filata” is the Italian name for types of cheese that in English are called Pasta Filata cheeses, characterized by an “elastic” string curd, e.g. Mozzarella and Provolone. A production line is presented in Figure 14.34.
The typical Mozzarella cheese was originally, and still is, based on buffalo milk derived from the buffaloes bred in central Italy. Mozzarella is also produced from a mixture of buffalo and cow milk, but nowadays, most commonly from cow milk alone. We have "high moisture" mozzarella, which is known as the balls packed in whey and often consumed together with tomato, oil and basel, for example. The other type is "low moisture" mozzarella, which in fact is the pizza cheese sold in blocks or pre-shredded.
Production of Mozzarella typically involves:
- Curd production in the usual manner
- Cheddaring, including milling, but not salting
- Cooking and stretching to obtain the elastic, stringy character
- Forming, hardening and brining
- Packaging, e.g. in plastic bags. For consumer size packages it is packed together with some brine
- Short storage before dispatch
Fat-standardized pasteurized milk is converted to curd in the usual way. After that, the curd and whey are pumped to a mechanical cheddaring machine (2) of a somewhat simpler type than that used for Cheddar cheese production, where the curd is matted and milled into chips. The matting and milling process takes about 1.5 hours.
After cheddaring, the chips are transported into the receiver of a cooker-stretcher (4). The plasticized curd is then continuously extruded to the moulding machine (6), en route to which it may be dry-salted (5) to shorten the normal brining time of about eight hours to approximately two hours.
The curd is worked into the (multi-)mould, which is then conveyed through a hardening tunnel, where the cheese is cooled from 55 – 65 °C to 35 – 45 °C, by spraying chilled water over the moulds. At the end of the tunnel, the moulds pass a de-moulding device.
The cheese falls into the gently flowing, cold (2 – 5 °C) brine bath and the empty moulds are returned to the filling machine.
The cheese may be bagged and packed in cartons, before being loaded on a pallet, which is then trucked to a store.
Semi-hard, semi-soft and soft types of cheese
Sometimes it is difficult to classify a type of cheese as distinctly semi-hard or semi-soft, or as semi-soft or soft, as some types occur in intermediate forms. The Tilsiter types are typical representatives of the former intermediate forms, as are blue or blue-veined types of cheese, while Brie types may represent the latter.
The following brief descriptions refer to methods of production of:
- Blue (veined) cheese, representative of semi-hard and semi-soft types ofcheeses with inside mould formation by Penicillium roqueforti.
- Camembert cheese, representative of semi-soft/soft types of cheese with outside surface mould formation by Pencillium camemberti andPenicillium candidum.
- Cottage cheese and Quarg as representatives of soft fresh cheese.
Semi-hard and semi-soft cheese
The prototype of blue-veined cheese is Roquefort, which originates from the community of Roquefort in the Aveyron Departement in France.
Roquefort cheese is produced from sheep milk; if any other kind of milk is used in the production of a similar type of cheese, it must not be called Roquefort cheese. Blue-veined cheese is the generic name for cheeses that develop an interior blue-green mould. Other well-known representatives of the blue-veined group of cheeses are British Stilton, Danish Blue and Italian Gorgonzola.
To imitate the characteristic flavour of Roquefort cheese as closely as possible, cheese milk from cows should be partially homogenized, i.e. standardized by mixing skim milk with homogenized cream of about 20 %
fat. The reason is that fat which has been exposed to homogenization is more sensitive to the influence of the lipolytic enzymes emanating from the inoculated Penicillium roqueforti mould.
After fat standardization, the milk is normally pasteurized at about
70 °C, cooled to 31 – 32 °C and fed to the cheese tank. After addition of an ordinary starter culture and a spore suspension of P. roqueforti, the milk is gently but thoroughly agitated to obtain good distribution of the microorganisms before renneting.
The principle of blue cheese production is shown in the block chart in Figure 14.35. As this block chart is self-explanatory, only short comments are given here.
The cheese is pierced after about five days in the ripening store to facilitate admission of the oxygen needed for the growth of the mould. Piercing is done using a tool with needles about 2 mm in diameter and roughly equal in length to the height of the cheese. The number of needles depends on the diameter of the cylindrical cheese, which is often pierced alternately through the top and bottom, to avoid the risk of cracking. A piercing machine is shown in Figure 14.36.
During the ripening period of five to eight weeks at 9 – 12 °C and an RH of >90%, the cheese rests on edge, normally on cupped shelves or on pivoted rods, as shown in Figure 14.37. The latter system facilitates turning of the cheese, which is done frequently to maintain the cylindrical shape.
After the pre-ripening period, the cheese is passed through a washing machine, to remove the smear that normally develops at the high RH in the store, as well as mould. After washing, the cheese is usually wrapped in aluminium foil or plastic film before being transferred to storage at about 5 °C, from which it is dispatched to a retail store after a couple of days.
Camembert may serve as the characteristic type of cheese covered by white mould from Penicillium camemberti and Penicillium candidum. Brie is another representative.
The cheesemaking procedure is broadly the same as for blue-veined cheese.
The cheeses are, however, small and flat. Self-pressing in the moulds proceeds for about 15 – 20 hours, during which time the cheeses should be turned about four times. The cheese is then brined for 1.0 – 1.5 hours in saturated brine (about 25 % salt).
After salting, the cheeses are placed on stainless steel string racks, Figure 14.38, or trays. The racks are stacked as much as 15 – 20 high, and then trucked into a storeroom at 18 °C and 75 – 80 % RH, where they are dried for two days. Then the cheese is trucked to ripening storage at 12 – 13 °C and 90 % RH.
The cheeses are frequently turned during the ripening period. When the white mould is sufficiently developed, normally after 10 to 12 days, the cheese is packed in aluminium foil and often put in a box, before being transferred to a cold store, where it is held at 2 – 4 °C, pending distribution to retailers.
Cottage cheese is a creamed fresh curd, low in acidity due to the coagulation of the milk by reaching the iso-electrical point, pH about 4.7. The final curd is washed and covered with a dressing.
The producer of Cottage cheese can choose between three ways to make a product of identical character:
- Long-set method
- Medium-set method
- Short-set method
The basic differences between these methods are summarized in Table 14.4.
Irrespective of method, after cutting, the curd is left undisturbed for 15 – 35 minutes. At the cutting stage, the cheese maker normally makes another choice, such as whether to produce small curd, medium-sized curd or large curd Cottage cheese, which is a matter of the fineness of the grains obtained at cutting.
Following the resting period and stirring, the curd is cooked – usually by indirect heating – for 1 – 3 hours, until a temperature of 47 to 56 °C is reached.
When the complete Cottage cheese production process takes place in the same tank, a certain volume of whey is drained off to make room for a corresponding volume of washing and cooling water.
When the same tank is used for the complete production, the curd is normally washed with three batches of water at temperatures of 30 °C, 16 °C and 4 °C respectively. Thorough washing dilutes the lactose and lactic acid, and further acid production and shrinkage are stopped by cooling the curd to about 4 – 5 °C. The total time for washing, including intermediate whey-water drainage periods, is about 3 hours.
After all the water has been drained off, pasteurized (80 – 90 °C) cream at 4 °C containing a small amount of salt, known as dressing, is added and thoroughly worked in. Ordinary Cottage cheese contains approximately 79 % moisture, 16 % milk-solids-non-fat (MSNF), 4 % fat and 1 % salt.
Finally, the Cottage cheese is packed in containers and stored at 4 – 5 °C before being distributed to retail shops.
The description shows that Cottage cheese can be produced in a single tank. However, special washing and creaming systems have been developed to rationalize production, especially the washing of the curd and the dressing. The principle of a rationally functioning Cottage cheese production line is illustrated in Figure 14.39.
From the enclosed curd producing tank (1), which serves among other things to protect the milk from airborne infection during the long (16 – 20 hours) or relatively short (5 hours) coagulation period, the whey-curd mixture is pumped via a static whey strainer (3) to a cooling/washing (CW) tank (4).
While the whey is passed to a collection tank, the curd falls into the CW tank with a certain level of fresh water. Even before all the curd from the cheese tank has been transferred to the CW tank, fresh water is pumped in through the bottom inlet. At a certain level in the tank, there is an outlet for the surplus liquid, which passes an inner, perforated part so that the curd is retained. After some minutes, when the surplus liquid is more or less free from whey, the inflow of water is stopped and the water is circulated through a plate heat exchanger (2), where the temperature is gradually lowered to 3 – 4 °C. The whole cooling and washing procedure takes about 30 – 60 minutes, not including filling and emptying of the CW tank.
After washing and cooling, the curd is pumped via a drainer (5) to a creamer (6), designed for mixing the curd and cream dressing. Finally, the creamed Cottage cheese is packed in cups and stored in containers.
Quarg is defined as “a sour skim milk curd cheese usually consumed unripened”. Quarg is often mixed with cream, and sometimes also with fruit and seasonings. The standard of the product varies in different countries and the dry matter in non-fat Quarg may vary between 14 and 24 %. Quarg can be made in a traditional way as fresh curd but nowadays more and more quarg is produced with separator techniques.
When the Quarg separator was first introduced, the milk was pasteurized at approximately 73 °C, before fermentation and separation. This is referred to as the traditional method.
Nowadays, it is more common to use high-temperature, long-time
pasteurization of the skim milk, 85 – 95 °C for 5 – 15 minutes, and further heat treatment of the acidified milk before separation. The latter method is called thermization, and temperatures 56 – 60 °C for up to three minutes are recommended. This, together with high-temperature pasteurization of the skim milk, contributes to better yield.
A Quarg production line is illustrated in Figure 14.40.
After pasteurization and cooling to 25 – 28 °C, the milk is routed into a tank (1). A bacteria culture, typically containing Streptococcus lactis/cremoris bacteria, is also added, often together with a small amount of rennet, normally one-tenth of what is used in ordinary cheese production or about 2 ml liquid rennet per 100 kg milk. This is done to obtain a firmer coagulum.
A coagulum forms after about 16 hours at pH 4.5 – 4.7. After the coagulum has been stirred, Quarg production starts with thermization (3) and cooling to 37 °C. The next step is centrifugal separation (4). The Quarg leaves the machine through nozzles at the periphery of the bowl and is discharged into a cyclone from which it is forwarded by a positive displacement pump via a plate cooler (5) into a buffer tank (6). The whey is collected from the separator outlet.
The final cooling temperature depends on the total solids content and, in fact, on the protein content. At a dry matter content of 16 – 19 %, the cooling temperature is 8 – 10 °C. When the DM is 19 – 20 %, the Quarg should only be cooled to 11 – 12 °C.
Tubular coolers are also used, but they are uneconomical for small production volumes, because the losses of product expressed as a percentage of the feed are high, owing to the large hold-up volume of the tubular cooler.
The cooled product is normally collected in a buffer tank before being packed.
If the Quarg is creamed, an adequate volume of sweet or cultured cream is added to the flow and subsequently mixed in a dynamic mixing unit (8), before the product goes to the packaging machine (9).
Sometimes, there is a demand for a long-life Quarg product. The process includes heat treatment of the product to inactivate all microorganisms. Suitable stabilizers must be added in the buffer tank and thoroughly distributed by agitation. They are needed to stabilize the protein system prior to the final heating, which is performed in a plate, tubular or scraped surface heat exchanger.
The Quarg processing line outlined here can also handle production of strained yoghurt, Labneh, or Tvorog, as well as being a part of a cream cheese processing line.
Processed cheese is made by further processing of finished cheese, usually a blend of hard rennet varieties with different aromas and degrees of maturity.
There are two types of this cheese:
- Cheese blocks with a firm consistency, high acidity and relatively low moisture content
- Cheese spreads with a soft consistency, low acidity and high moisture content
Various flavourings can be added. Varieties with a smoked flavour can also be included under this heading.
Processed cheese usually contains 30 or 45 % fat, calculated by total solids, though varieties with lower or higher fat contents are also made. The composition in other respects depends entirely on the moisture content and the raw materials used in the manufacture.
Cheese for processing is of the same quality as cheese for direct consumption. Cheese with defects regarding surface, colour, texture, size and shape, as well as cheese with a limited shelf life, can also be used for processing, as can fermented cheese where the fermentation has been caused, for example, by coliform bacteria, provided that it is free from off-flavours. Butyric-acid fermented cheese can cause problems, as the bacteria may cause fermentation in the processed cheese.
High-quality processed cheese can only be produced from high-quality raw materials.
The manufacturing process begins with scraping and washing the cheese, which is then ground. In large factories, the shredded cheese is melted continuously. In smaller plants, it is transferred to cookers (of which there are several types).
Firstly, water, salt and emulsifier/stabilizer are mixed into the cheese. The mixture is heated to 70 – 95 °C, or even higher (depending on the type of processed cheese), in steam-jacketed cookers and by direct steam injection. This speeds up the cooking time of 4 – 5 minutes for block cheese and 10 – 15 minutes for spreads. It is kept constantly agitated during heating, to avoid scorching. The process usually takes place under vacuum, which offers advantages from the point of view of heating and emulsification. The vacuum also removes undesirable odours and flavours, and makes it easier to regulate the moisture content. The capacity of a batch cooker is about 75 kg.
The pH of processed cheese should be 5.6 – 5.9 for spreads and 5.4 – 5.6 for sliced types. Variations in the pH of the raw material are adjusted by mixing cheese of different pH and adding emulsifiers/stabilizers to adjust the pH. The emulsifiers/stabilizers also bind calcium. This is necessary to stabilize the cheese, so that it will not release moisture or fat.
The processed cheese is then discharged from the cooker into a stainless steel container, which is transported to the packing station and emptied into the feed hoppers of the packing machines. These machines are usually fully automatic and can produce packages of different weights and shapes.
Normally, the cheese is hot-packed at cooking temperature.
The spreadable type of processed cheese should be cooled as rapidly as possible, and should therefore pass through a cooling tunnel after packing. Rapid cooling improves the spreading properties.
The cheese block on the other hand should be cooled slowly. After moulding, the cheese is left at ambient temperature.