In this article we will discuss about the twenty-three steps involved in the process of making Cheddar cheeses. Some of the steps are: 1. Record Keeping 2. Preparation of Equipment 3. Receiving Milk 4. Filtration/Clarification 5. Standardization 6. Pasteurization 7. Homogenization 8. Addition of Calcium Chloride 9. Adding Starter (Ripening) 10. Adding Colour 11. Renneting 12. Coagulation 13. Cutting and a Few Others.
1. Record Keeping:
The objects are:
(i) To evolve a standard process-schedule and technique for cheese manufacture and curing suitable to local factory conditions;
(ii) To study seasonal trends in the manufacture of cheese;
(iii) To assess the efficiency of manufacturing operations;
(iv) To trace backwards any variation in the manufacturing technique affecting the quality of the cured cheese;
(v) To control variations caused by climatic, biological and chemical conditions so as to obtain a standard finished product;
(vi) To collect basic data for computing the cost of cheese production.
2. Preparation of Equipment:
This refers mainly to cleaning and sanitization of cheese-making equipment and accessories. Cheese milk should be received and processed only in thoroughly cleaned and properly sanitized equipment. Insanitary conditions during manufacture will cause contamination, thereby impairing the quality of the finished cheese.
All cheese-making equipment and accessories should be sterilized just before use by contact with hot water (at 82°C/180°F) or chlorine solution (having 100 ppm available chlorine) for at least 2 minutes.
3. Receiving Milk:
It is well known that- ‘Only high-grade milk can yield high-grade cheese’; ‘The quality of finished cheese depends upon the initial quality of the milk from which it is made’; ‘Cheese is no better than the milk from which it is made’.
The milk grader in a cheese factory has to perform his task conscientiously from day to day. He should intercept any can/tanker of inferior milk and not allow it to get mixed up with high-grade milk. Successful cheese factories follow a system of daily, efficient grading of all milk received.
This consists of:
(i) Determining the odour of the milk in each can/tanker. No off-flavour should be accepted.
(ii) Inspecting the appearance of the milk, which should be free from all extraneous matter.
(iii) Determining sediment, either once a week or every ten days, in each can of milk. (A minimum amount of sediment is desirable.)
(iv) Performing MBR, Resazurin and Rennet-curd tests on the milk once a fortnight or so for each producer/supplier and more frequently (weekly or even daily) on milk of doubtful quality.
(v) Determining the percentage of titratable acidity. (There should be as little developed acidity as possible.)
(vi) Examining milk for bacteriophage, antibiotics and inhibitory substances.
After the milk has been examined for quality and accepted, it is weighed; then a representative sample is taken for determination of fat and casein contents, etc.
4. Filtration/Clarification:
The chief object of this step is to remove any visible dirt in milk so as to improve the aesthetic quality of the cheese made. The milk is usually pre-heated to 35-40°C for efficient filtration/clarification.
5. Standardization:
In cheese making, standardization refers to adjustment of the casein/fat ratio in cheese milk to 0.68-0.70.
The objects are:
(i) To regulate the fat in the dry matter of cheese;
(ii) To produce the maximum amount of cheese per kg. of fat in cheese milk.
Note:
Standardization should either be done correctly, or avoided altogether.
Problem:
Standardize 1000 kg. milk testing 4.5% fat and 2.7% casein so that C/F ratio is 0.70. Available- Skim milk testing 2.8% casein. (Neglect the fat in the skim milk.)
Solution:
In given milk,
Fat = 1000 × 4.5/100 = 45 kg.
Casein = 1000 × 2.7/100 = 27 kg.
In standardized milk,
Casein = 45 × 0.70 = 31.5 kg.
Extra casein requited = 31.5 — 27 = 4.5 kg.
Hence
Skim milk required = (4.5/2.8) × 100 = 161 kg. Ans.
Note:
This is a rough method.
6. Pasteurization:
The usual temperature-time employed for pasteurization of cheese milk is:
1. Holder—63°C for 30 min.
2. HTST—71°C for 15 sec.
Objects:
The objects or advantages of pasteurizing cheese milk are:
(i) To destroy all pathogens;
(ii) To destroy fault-producing micro-organisms;
(iii) To produce a more uniform product of high quality;
(iv) To increase the yield.
Limitations:
The chief limitations of pasteurization are:
(i) It destroys the typical flavour and body of cheese;
(ii) It entails a longer ripening period;
(iii) It encourages the use of low-quality milk;
(iv) It increases the overall cost of cheese making.
Note:
The advantages of pasteurization heavily outweigh its disadvantages.
7. Homogenization:
Advantages:
(i) Lower fat losses in whey and thereby a higher yield of cheese;
(ii) Reduced fat leakage of cheese at elevated temperatures;
(iii) Increased rate of fat hydrolysis in some cheeses, such as blue cheese.
Disadvantage:
A softer curd is formed, which necessitates modifications in the cheese-making process.
Note:
Because of the disadvantage, cheese milk is normally not homogenized.
8. Addition of Calcium Chloride:
Excessive heat-treatment causes the precipitation of a part of the calcium salts in milk. This results in slower renneting action and a weaker curd, which can be corrected by the addition of 0.01-0.03 per cent calcium chloride to milk.
9. Adding Starter (Ripening):
Ripening or souring of milk refers to the development of acidity in milk from the time it is received in the cheese vat until renneting. In cheese milk, ripening is done by the addition of starter.
The starter is the ‘heart’ of cheese. A bad starter is almost certain to give low-quality cheese. A good starter may make up for other defects, such as contaminated milk. There are different kinds of cheese starters, such as those producing acids, aroma, special effects (such as ‘eyes’), etc. A cheddar cheese starter usually contains Str. Lactis and/or Str. Cremoris.
The usual time to add the starter is before all the milk has been received in the vat. The amount of starter added is to the extent of 0.5 to 1 per cent of the milk, and the temperature of addition is 30- 31°C (86-88°F). Before being added to the milk, the starter should be examined for its quality; it should then be stirred until smooth and creamy in consistency; then strained and added in the required quantity, and mixed thoroughly and uniformly into the milk.
Ripening (or addition of starter) aids in:
(i) The formation of desirable curd;
(ii) Establishing a favourable bacterial flora (and checking the growth of undesirable micro-organisms);
(iii) Controlling moisture.
Note:
Ripeness in milk is measured by: titration (for acidity); rennet test; and pH metre.
10. Adding Colour:
When colour is used, it is added just before renneting. The usual amount is 30 to 200 ml. or more (for buffalo milk) for 1000 kg. Milk. The colour is diluted with approximately 20 times its volume of (potable) water for even distribution. It is vigorously agitated to ensure uniform and rapid distribution. The colour of cheese is usually an alkaline solution of annatto. Rennet and colour should not be mixed together before being added to the milk.
11. Renneting:
Adding rennet to milk in cheese making is commonly known as renneting or setting.
What is Rennet?
It is the crude preparation or extract from the abomasum Rennet contains two principal enzymes, viz., rennin and pepsin. Rennin is an extremely powerful clotting enzyme, which causes rapid clotting without much proteolysis. On the other hand, pepsin induces proteolysis, leading to bitterness in cheese. Rennet is available as a liquid or powder or as tablets.
How is it Prepared?
Rennet is the preparation obtained commercially from the fourth or true stomach (abomasum) of the young calf, known as the veil. The lining of the stomach is washed, dried, cut into small pieces and macerated into water containing about 4 per cent boric acid at 30°C for 5 days. Milk-fed calves yield the purest rennet.
Alternatively, a brine extract at 15-20°C may be prepared. A common method is to dry the veils by inflation and afterwards cut them into strips and extract with brine, i.e. sodium chloride solution (up to 10 per cent) for a few days. Preservatives such as boric acid are commonly added.
Note:
The pioneer in the commercial manufacture of rennet was Christopher Hansen (Danish) who established his first rennet factory in 1874. The Hansen brand of rennet is world famous.
How is it Stored?
The essential properties of a commercial rennet are high activity, stability (constant strength) and a reasonable bacteriological purity. Rennet is commonly supplied in barrels, stone jars or plastic containers. Commercial rennet should be stored in a closed vessel, in a dark room at below 10°C. It should not lose more than 1-2 per cent of its strength per month.
Properties of Rennin:
This is a sulphur-containing protein. One part can clot about 5 million parts of milk. In cheese making, one part of liquid rennet (about 2 per cent protein) is used for about 5000 parts of milk. Being an enzyme, it is easily destroyed by heat, many chemical substances and some physical conditions. It is very sensitive to alkali. Heating to 70°C at pH 6.8-7.0 will destroy it in 14 minutes.
Factors Affecting Rennin Action:
(i) Temperature:
Below 20°C, rennin is almost inactive. From 30 to 48°C, it is about equally active, the optimum being 41°C. Above 50°C, the activity falls off rapidly.
(ii) Acidity:
The rate of clotting increases rapidly with small increases in acidity. Alkalis considerably retard the clotting of milk by rennet.
(iii) Calcium ions:
These have little, if any, effect on the first (enzymic) stage of rennin action, while the coagulation of milk (second stage) is very sensitive to changes in concentration of calcium ions. It is common practice to add calcium chloride to milk which has been severely pasteurized, e.g. at 80°C for 30 seconds. This acts in three ways by lowering the pH value, increasing the calcium ion concentration, and raising the colloidal calcium-phosphate content.
(iv) Inhibitory Substances:
Many colloidal substances interfere with rennin coagulation, e.g. albumin, serum peptone, etc. Albumin and globulin retard coagulation. (Mastitis milk clots slowly with rennet; the alkalinity of such milk also contributes to this effect.) Boiling, resulting in denaturation of the proteins, removes the inhibitory effect. Five per cent ‘peptone’ almost prevents clotting.
(v) Homogenization:
This has an accelerating effect on rennet clotting, but decreases the curd tension.
(vi) Heating of Milk:
Heat not only destroys rennin but also makes clotting of the milk by the enzyme less easy. The major reason for this is the removal or precipitation of calcium ions.
(f) Rennet Preparations Other than Calf Rennet:
These include goat and lamb rennets, plant enzyme’s such as withania coagulans, ficus, papain, etc.
(g) Difference in Behaviour between Animal and Vegetable Rennet:
Although vegetable rennets clot both cow and vegetable milks, animal rennets do not clot vegetable milks even if the calcium content is raised to that of cow milk.
(h) Bacterial Rennet:
The use of enzymes from micro-organisms, particularly aerobic spore-formers (Bacillus Subtilis) and some of the gram-negative rods (Scrratia Marcescens) is a fairly new development in cheese technology.
(i) Adding Rennet:
Rennet is added when it has been determined that the acid is developing at the desired rate. Thus, when making cheese from ripened milk, rennet is added when the acidity has increased from the initial level by 0.02 per cent. The ideal temperature for setting raw milk under normal conditions is 30°C (86°F), and for pasteurized milk, 31°C (88°F). The amount of rennet extract used should be such as to form curd that is firm enough to be cut in 25 to 30 minutes after the addition of rennet.
The amount of rennet which should be added depends on:
(i) Strength of the rennet;
(ii) Temperature of milk;
(iii) Acidity of milk; and
(iv) Composition of milk.
Usually, liquid rennet is added @ 15 to 25 ml. per 100 litres of milk. The rennet is diluted with 20 to 40 times its volume of (potable) water before it is added, to ensure proper distribution for uniform coagulation. The milk is thoroughly stirred during the addition of the rennet and also for 3 to 5 minutes afterwards. The vat is covered as soon as the stirring is over, to keep the surface warm and protect it from contaminating dust particles.
12. Coagulation:
This refers to liquid milk changing to a semisolid junket. The first signs of coagulation are that bubbles of air stirred into the milk surface take longer to break and a spatula dipped into the milk and withdrawn shows small flakes of curd.
13. Cutting:
This refers to the cutting of the ‘firm’ coagulum into cubes of a specific size.
(a) When to Cut Curd:
When a (sanitized) glass rod inserted at a 45° angle and lifted straight up makes a clean break in the curd, it is ready for cutting If the curd is cut too soon, there will be a lower yield of cheese; if cut too late, cutting will be difficult and moisture expulsion delayed.
(b) Curd Knives:
These consist of stainless steel wires or strips, 6 or 9 mm. apart, one horizontal and the other vertical.
(c) Method of Cutting:
The curd is usually first cut with the horizontal knife lengthwise, then with the vertical knife lengthwise and widthwise.
(d) Syneresis of Cheese Curd:
This refers to the expulsion of whey and contraction of the curd. From the cheese-making point of view, the factors controlling the loss of whey and contraction of the coagulum are- cutting, temperature, acidity, agitation, time and salt.
(e) Behaviour of Curd after Cutting:
After the curd is cut, whey begins to appear between the cubes and a film begins to form on the outer surface of each cube. This film should not harden, i.e. become firm, too rapidly. Care has also to be taken to avoid breaking this film.
(f) Acidity of Curd after Cutting:
Decreases by 0.05 to 0.08 per cent from that of milk at renneting.
(g) Stirring Curd after Cutting:
During the first 2-3 minutes after cutting, the curd is not stirred. Then gentle stirring starts. The speed of stirring increases with the gradual firming of curd cubes. Matting is indicative of inadequate stirring.
14. Cooking:
This refers to the heating of curd cubes; it begins within 15 minutes of cutting.
(a) Regulation of Heating:
The heat is applied slowly to begin with. If the temperature is raised too rapidly, a condition similar to ‘case-hardening’ will result, and the curd cubes will be hard on the outside but soft and ‘water-logged’ inside. The rate of heating is such that the temperature rises to 32°C in about 15 minutes and thereafter to the maximum cooking temperature (37 to 39°C) at the rate of 1°C every 4 minutes.
(b) Amount of Heat Required:
This depends chiefly on the type of cheese required. For cheddar, a maximum temperature of 37 to 39°C is normal. Too high a temperature can reduce the souring rate and activity of starter organisms.
Note:
If acidity is developing faster, then a faster rate of heating and cooking to a higher-temperature-than-normal is necessary, and vice versa.
15. Drainage of Whey (Dipping):
This refers to the removal of whey from the curd. When the curd cubes have been reduced to about one-half of their size at cutting, the acidity approaches a desirable limit and the cubes attain a desirable consistency (elastic feel when squeezed), stirring is stopped and the cubes are ‘pitched’. (Pitching refers to the curd cubes being dropped to the bottom of the vat and piling them up together.)
The curd cubes are pushed away from the gate of the vat, a strainer is inserted in the gate, a curd-pail is hung on the curd outlet and the whey is drawn from the vat. In actual practice, especially with large vats, it is desirable to remove one-half of the whey before the curd is quite ready so as to make quick removal of the remaining whey possible at the proper time.
16. Cheddaring:
This refers to the combined operations of packing, turning, piling and repiling the curd cubes.
(a) Packing:
After the bulk drainage of whey, the curd cubes are kept closely together in two heaps with a channel in between (for continuing the whey removal process). This is known as packing, and takes 5 to 15 minutes after dipping. It results in the formation of two long slabs of curd. These are cut with a cheese knife into blocks or strips 15 to 20 cm wide.
(b) Turning:
As soon as the blocks (strips) of curd can be handled without breaking, they are rolled bottom-side up in the vat. This is called turning and is carried out every 15 minutes till the curd is ready for milling and salting.
Note:
The vat is kept covered and the temperature of the curd maintained at about 32°C.
(c) Piling and Repiling:
Within 30 to 45 minutes of packing, blocks of curd are turned and laid one over another in twos or threes. This is called piling. Then the position of the curd blocks is altered and this is known as repiling.
(d) The cheddaring operation usually lasts two hours or more and is very important not only for moisture control but also for improving body and texture. After cheddaring, the curd becomes drier, more mellow and silky and changes from a sorbo rubber-like material to one resembling chicken breast-meat. In the later stages, it tends to tear apart in fibrous shreds and develops a characteristic nutty and buttery aroma.
The end of the cheddaring operation is indicated by:
(i) Titratable acidity- 0.30-0.35 per cent more than at cutting.
(ii) Hot iron test- long threads, 12 mm or slightly more.
(iii) pH- About 5.4.
17. Milling:
This refers to the mechanical operation of cutting the blocks of cheddared curd into small pieces with the help of cheese mill.
Objects:
These are:
(i) To promote the further removal of whey;
(ii) To enable quick distribution of salt in the curd;
(iii) To prepare curd for pressing into final form;
(iv) Other benefits include: de-odourization; cooling of curd, through more rinsing if needed; and making cheese more uniform in composition.
Types of Mill:
The curd mill may be hand or power-driven. Milling is done in such a way that the cut curd falls into the vat itself. The curd pieces are stirred gently to prevent matting.
Note:
(i) Milling normally releases a small amount of whey from the curd.
(ii) After milling, the curd pieces may be rinsed with water to improve their physical condition for salting and pressing.
18. Salting:
This refers to the addition of common salt to the curd pieces. Salt in cheese affects flavour, body and texture, and keeping quality. Cheeses without salt are soft, ripen quickly and rapidly develop unpleasant flavours.
Objects.
These are:
(i) The further removal of whey;
(ii) Hardening and shrinking of curd;
(iii) Retarding further formation of lactic acid;
(iv) Checking undesirable fermentation;
(v) Producing desirable quality characteristics.
Holding before Salting:
Salting may be delayed (by more than 15 minutes if needed) when it seems desirable to develop more acid in the cheese curd to encourage further drainage of whey, or to aerate the curd to improve its flavour.
When Done:
Cheese curd is normally salted:
(i) About 15 minutes after milling;
(ii) When a hot iron test shows threads 1 to 2 cm. long;
(iii) When acidity is 0.4 to 0.5 per cent; and
(iv) When pH is 5.4 to 5 0.
Amount of Salt Added:
This depends on the amount of curd in the vat and salt content desired, and generally varies from 1 to 2 per cent (average 1.5 per cent).
Note:
Both under-salting and over-salting of cheese are undesirable: while under-salting produces a weak and pasty body, open texture and abnormal ripening, over-salting produces a harsh body, slow ripening, close texture and cracked rinds.
Methods:
The curd is salted in one of the following ways:
(i) Direct addition- One-third of the calculated amount of salt is added to the curd in the vat in three applications;
(ii) Rubbing salt on the surface of the cheese;
(iii) Floating the cheese in 18-20 per cent brine.
Quality of Salt:
Same as for butter.
Note:
After the curd has been salted, there is no danger of matting.
19. Hooping:
This refers to the curd being placed in hoops or moulds in which the cheese curd is pressed into its final shape.
Condition of Curd at Hooping:
The salt should have dissolved completely and the curd should feel mellow and silky.
Temperature at Hooping:
Should be 30-32°C. Hooping and pressing at too high a temperature cause an excessive loss of fat, decreased yield, development of abnormal flavours and exaggeration of bacterial defects. On the other hand, hooping and pressing at too low a temperature result in an open texture, imperfect rind formation and lack of whey drainage.
Note:
Before filling, cheese-curd is weighed accurately enough so as to make cheeses of uniform size.
20. Dressing:
This refers to the arrangement of the cheese cloth before and after pressing.
Before Pressing:
Large cheese hoops are lined with cloth before they are filled with cheese curd for pressing. Small hoops are filled with curd and pressed for 30-60 minutes without any cloth. A cloth is necessary to form a closed rind or surface. The hoops are carefully lined with cloth in order to produce a smooth surface in the finished cheese.
After (First) Pressing:
To remove all wrinkles formed during pressing.
21. Pressing:
This refers to the operation of forcing the particles of milled and salted curd in the hoops into the smallest possible space.
Object:
To give cheese its final shape.
Method:
The curd is pressed in two stages:
(i) Preliminary or First Pressing:
This shapes the cheese and reduces it to almost its final volume. It ends after 30-60 minutes when the cheese is dressed.
(ii) Final Pressing after Dressing:
This lasts for 6 to 20 hours (average 15 hours).
The average pressure applied on round hoops is around 70 psi and on square hoops 25 psi. While pressing, some whey comes out of the cheese curd. Also, the air-spaces and whey-pockets are closed up by the curd. Pressure is applied lightly and gradually at first, but rapidly enough to prevent the curd settling at the bottom of the hoops. Full pressure is reached in about 30 minutes. Too much initial pressure traps whey in the openings between the curd particles and tends to produce on open texture.
Types of Press:
Cheese presses may be of the following types:
(i) Screw;
(ii) Pneumatic;
(iii) Hydraulic;
(iv) Spring—in this, full pressure is maintained all the time.
22. Drying:
This is done for rind formation in cheese.
It involves the following steps:
(i) Taking the Cheese Out of the Hoop:
Care is taken to see that the cheese removed from the hoop is neat, clean, uniform in size and regular in shape.
(ii) Stamping the Cheese:
The date, batch number, variety, name, etc., are stamped on the cheese for identification and record.
(iii) Keeping cheese in a drying room, where the temperature is maintained at 12 to 16°C (55-60°F) and the average relative humidity at 50 per cent for a few days. The cheese is turned at 24-hour intervals so that both ends and sides of the cheese can dry and form the desired rind.
Note:
Mould control in the drying room is important.
23. Paraffining:
This refers to the operation of dipping the cheese for a few seconds in a bath of melted paraffin, whereby a thin coating of paraffin is applied to the surface of the cheese.
Objects:
(i) To reduce loss of moisture during curing;
(ii) To prevent extensive mould growth (paraffin, however, is not mould-proof;
(iii) To protect it against insects (as long as the cheese is free from cracks).
Kinds of Paraffin:
(i) Paraffin Wax:
This is a product of the petroleum industry. The type used for cheese has a melting point of 51-52°C (125- 127°F).
(ii) Micro-Crystalline Wax:
More water and vapour-resistant.
(iii) Flexible Waxes:
These are combinations of paraffin and 16 (45- 19/1981) micro-crystalline waxes. They are frequently coloured (red, brown, black, etc.) for an identification of the cheese.
Note:
The samples of cheese for analysis are taken before paraffining.
Procedure:
The following steps are involved:
(i) Melting of paraffin in a steel tank. Only that quantity of paraffin is used which avoids overflow when the cheese blocks are dipped in it.
(ii) Keeping the cheese-blocks, a few at a time, on metal racks (with wooden slats) on which the blocks rest on their curved surfaces while being dipped.
(iii) Maintaining the temperature of liquid paraffin in the tank at 104-121°C (220-250°C). Both over-heating and under-heating are avoided for best results.
(iv) The cheese blocks are dipped quickly and completely, held under paraffin for about 5 seconds, and allowed to drain for 10 seconds or until they can be handled without rubbing off the paraffin coating.