Method of cheese manufacture.

Cheese manufacture is essentially a dehydration process in which fat and casein in milk are concentrated between 6-12-fold, depending on the variety. The degree of dehydration is regulated by the extent and combination of the above five operations, in addition to the chemical composition of milk. In turn, the levels of moisture and salt, and pH and cheese microflora regulate and control the biochemical changes that occur during ripening and hence determine the flavor, aroma and texture of the finished product. Thus the nature and quality of the finished cheese are determined to a very large extent by the manufacturing steps. However, it is during the ripening phase that the characteristic flavor and texture of the individual cheese varieties

develop.

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

A major cause of variation in the characteristics of cheese is the species of dairy animals from which milk is obtained. The principal dairying species are cattle,buffalo, sheep and goats, which produce 85%, 11%, 2%, and 2% of commercial milk, respectively. Goats and sheep are significant producers of milk in certain regions, e.g. around the Mediterranean, where their milk is used mainly for the production of fermented milks and cheese. Many world famous cheeses are produced from sheep’s milk, e.g. Roquefort and Feta and Romano; traditional Mozzarella is made from buffalo milk. There are very significant differences in the composition and physicochemical properties of milk, which are reflected in the characteristics of cheese, produced there. Some varieties are always made from the milk of the sheep, goat or other particular mammal. There are significant differences in milk composition between breeds of cattle, which influence cheese quality.

The milk should be of good microbiological quality, as contaminating bacteria are concentrated in the curd and may cause defects or public health problem.However, cheese milk is usually pasteurized or subjected to one or more of the treatments to render it free of pathogenic or food poisoning and certain spoilage bacteria.Factors inhibiting starter growth, giving slow coagulation and producing taints and gas lower the quality of resulting cheese. The starter aspect is very prominent and there is considerable truth in the statement that starter is 90% of the cheese making. Bulking of the milk in factory cheese making has almost entirely eliminated of these factors, This is particularly true for mastitis, inhibitory substances of physiological origin, preservatives and taint substances already in milk, because it is unlikely that all producers’ milk would be seriously affected by all these on the same day.

ii. Standardization of Milk: The composition of cheese is prescribed in ‘Standards of Identity’ with respect to moisture and fat in dry matter, which in effect defines protein: fat ratio. The moisture content of cheese, and hence mainly the manufacturing protocol and the protein determine the level of protein and fat ratio in cheese which in turn is determined by the casein: fat ratio in the milk. Fat and casein together with moisture left in the curd control cheese yield,

but fat also has a marked effect on appearance and feel of the curd and cheese.When ratio of casein to fat is high, the curd is more leathery and the final cheese does not acquire the mellow, velvetiness of a whole milk cheese. Skim milk cheeses are usually consumed “green”. In general, the casein : fat ratio in milk should be about 0.7 for good quality cheese. Depending on the ratio required,it can be modified by: (a) removing some fat by natural creaming or centrifugation,(b) adding skim milk, (c) adding cream and (d) adding milk powder.

Heat Treatment of Milk: Traditionally, cheese was made from raw milk, a practice that was almost universal until the 1940s. Although cheese made from raw milk develops more intense flavour than that produced from pasteurized milk, the former is less consistent and poses a public health risk. When cheese was produced from fresh milk on farms or in small, local factories, the growth of contaminating microorganisms was minimal but as these factories became larger, storage of milk for longer periods became necessary and hence the microbiological quality of milk deteriorated and varied. Thermization of cheese milk is fairly widely practiced on receipt at the factory to reduce the microbial load and extend the storage period. For public health reasons, it became increasingly popular from the beginning of the twentieth century to pasteurize milk for liquid consumption. The pasteurization of cheese milk became widespread about 1940, primarily from public health reasons, but also to provide a milk supply of more uniform bacteriological quality. Although a considerable amount of cheese is still produced from raw milk, especially in

Southern Europe (including such famous varieties as Swiss and Emmental) pasteurized milk is generally used, especially in large factories.

Pasteurization alters the indigenous microflora and facilitates the manufacture of cheese of more uniform quality, but unless due care is exercised, it may damage the rennet coagulability and curd- forming properties of milk.Even when properly pasteurized, Cheddar cheese(and probably other varieties) made from pasteurized milk develops a less intense flavour and ripens more slowly than raw milk cheese. Severe heat induces changes, e.g. inactivation of indigenous milk enzymes, killing of indigenous microorganisms, denaturation of whey proteins and their interaction with micellar k-casein, perhaps even shifts in salt equilibria and destruction of vitamins, could be responsible for these changes. Until now it has not been possible to establish which of these factors was principally responsible for the differences in quality between raw and

pasteurized milk cheese. Therefore, normally subpasteurization temperature is preferred to heat cheese milk, which is termed as ‘thermization’.

Thermization (65 0C/15 s) of cheese milk on arrival to factory is common or standard practice in some countries. The objective is to control psychrotrophs and milk is normally pasteurized before cheese making.

iv. Ripening of Milk (Acidification): The formation of acidity in the milk to be used for cheese making known as “ripening” is usually brought about by starter culture. The acidity development inhibits the growth of undesirable organisms and influences the rate of coagulation. When the desired acidity (0.01% increase) is reached, most varieties of cheese require the addition of rennet to the ripened milk in order to obtain a curd of the desired characteristics. This process of acidification continues during the manufacture of most, if not all, cheese varieties.

This process may last up to 24 h, and for some varieties during the early stages of ripening also, i. e. acidification commences before and transcends the other manufacturing operations. Until relatively recently, the indigenous microflora of milk was relied upon for acid production. Since this was probably a mixed microflora, the rate of acid production was unpredictable and the growth of undesirable bacteria led to the production of gas and off-flavours. It is now almost universal practice to add a culture (starter) of selected lactic acid bacteria to pasteurized cheese milk to achieve a uniform and predictable rate of acid production. For cheese varieties that are cooked to not more than 40 °C, a starter consisting of Lactobacillus lactis subsp.lactis and / or Lc. Lactis subsp.cremoris is normally used. For Cheddar cheese making the milk is heated to 29-31 °C with average of 30 °C. A culture of lactic acid bacteria about 0.75- 1.25% with the average of 1% is added after thorough blending of the starter to remove curd particles through a strainer. The milk is allowed to ripen for about 45-60 min. A rise of 0.02% in acidity is considered to be satisfactory for adding rennet.

v. Addition of Cheese Colour: The quantity of colour depends on the requirement for the intensity of the cheese colour. For light straw colour about 1/3 oz / 1000 lbs of milk and for deep yellow colour 2 oz / 1000 lbs is used.The milk is stirred thoroughly to ensure an even distribution of colour.

Setting the Curd: Milk is brought to the setting temperature ( 31°C ) by heating. The rennet is added in the form of solution at the rate of 1.5-2.5 g /100 depending on the type of rennet. The milk is thoroughly mixed for uniform distribution of the rennet. The coagulation is complete in about 20-30 min.

vi. Cutting the Curd: After the firm curd is formed, it is cut with cheese knives.The curd should be cut into small cubes about ¼-3/8 inch size. This is accomplished by cutting the curd length-wise of the vat with the horizontal knife and both length-wise and cross-wise of the vat with the vertical knife.Never permit the curd to get so firm that it pushes ahead of the knife. Conversely,never cut the curd when it is so soft, that it shatters. After cutting, allow the curd to remain undisturbed until the surface is completely covered with the whey. This resting period will reduce, to a degree, fat and curd losses in the whey through the development of a film on the outer surface of the curd. In addition, whey will form between the freshly cut cubes. During this period, titrate a clear sample of whey, free from curd, and record the results on the make record. If milk titrated 0.15 to 0.16 % acidity at setting when the rennet was added, the whey acidity at cutting should be 0.09 to 0.11%. Removal of the most of the casein and some of the phosphates by curd formation accounts for the decrease in acidity of the whey.Stir the curd when the surface of the curd is covered with whey and the individual particles are judged to have healed properly. The stirring should be started slowly after about 15 min of cutting. The curd should be stirred only enough to keep it from forming the lumps and matting. Too rapid agitation will shatter the curd. To make a firm, low moisture cheese, the curd should be stirred for 30 min after cutting before heat is applied. During this time the cubes expel whey and shrink in size favouring a more uniform cooking. Stirring the curd carefully for 30 min after cutting prevents the formation of a tough skin around each cube. This skin will retard or even prevent whey expulsion. The individual curd particles then retain soft center.

vii. The pitching of curd: This is the time when stirring of the curd particles ceases and they are allowed to fall to the bottom of the vat to form a mat. Like the cutting time, the decision as to when to pitch is not crucial, but the correct decision naturally leads to a better cheese. Generally the whey removal starts 21/4 hrs after adding rennet. Whey is removed from the curd by placing a screen strainer in front of the outlet of the vat. The curd remaining in the vat is then piled on each side of the vat to permit it to drain and mat. When the whey has drained, the whey acidity at packing should be from 0.18- 0.22%

viii. Packing: The curd should be packed on both sides of the vat leaving a narrow central ditch for whey drainage. Packing is considered to have begun when the whey has been drained and exposed curd has knit together sufficiently to be cut into slabs without crumbling. Cut the curd mass into slabs of 4” wide and give a half turn.

ix. Cheddaring: After removing the whey and piling, the curd is cheddared. It is this process which distinguishes cheddar cheese from many others. The slabs are turned at intervals of 15 mintues and piled two high and then 3 high as the cheddaring progresses. When the cheddaring process is completed, the small curd particles lose their identity completely, fusing together into a particularly solid mass of curd. Considerable whey is eliminated during the process. The fully cheddared curd has a dry, firm, mellow and meaty texture exhibiting chicken breast structure. It is free from openings at the time of milling. It is desirable to keep the curd warm while matting and cheddaring. The cheddaring may last for about 2 hours.

x. The Hot- Iron Test: One of the most characteristics changes in curd during Cheddaring is the acquirement of ductility or the capability of being drawn out into a thread when melted by heat. At the end of Cheddaring if an hot iron rod is brought in contact with the cheese block and drawn the thread length is 1 ½ - 2” long and the acidity should be 0.45-0.50%.

xi. Milling: After cheddaring the curd is passes through the curd mill which cuts the slabs of curd into strips about ½ - 1 inch wide and 2-3” long. Moisture or whey is eliminated during this process also.

xii. Salting the Curd:- The strips of the curd are stirred to prevent matting after milling and salt is sprinkled on the milled curd at the rate of 2.5% in three equal increments. The salt is applied uniformly because it diffuses very slowly thus it is very difficult to uniformly distribute in the finished product. After salting it is allowed to sit until hoped and pressed. Time from milling to salting is important. Shortening of time may cause defect in appearance. Salt creates osmotic pressure, water and CaPO4 are carried to surface. Thus at the surface there is a solution of salt and CaPO4. When NaCl starts diffusing inside cheese cubes the solubility of CaPO4 decreases and it precipitates out between particles.Thus white lines called seaminess are seen therefore, enough time should be given for CaPO4 to go out with the whey so that excessive amount of serum is not trapped.

Some salt is naturally lost in the whey when salt is mixed with the broken curd as in the cheddar process. In Cheddar cheese about 60% added salt is retained in the curd, 35% lost in the whey from press and 5% lost during salting and hooping.Salt in cheese together with acidity, lack of O2 and low temperatures is one of the major factors controlling the growth of microorganisms and so deciding the pattern of flora distribution.

Apart from the inherent salty taste of cheese quite different flavors would be obtained, if it were possible to make cheese without salt because of the different balance of micro flora which would be obtained, the proportion of common proteolytic, lipolytic and taint producing bacteria would be higher (these are normally only about 1% of the total in good Cheddar cheese) and the cheese would almost certainly possess an unpleasant odor and taste.

xiii. Hooping the Curd: After salting the curd is ready for the cheese hoop. The hoop is lined with a cheese cloth. In the bottom of the hoop is placed a starched cheesecloth and after the curd is placed into the hoop, it is covered with the remaining portion of the same cloth.

xiv. Pressing the Curd : The hooped curd is then placed in a cheese press where pressure is applied gradually at first and then increased as the curd cools to 75 KN/m2 for 12 –16 hours. Turn into fresh cloths and repress at 200KN/ m2 for a further 24 hours. The temperature of the curd should be high enough to permit the curd to fuse and to develop a closed rind. The normal pressing temperature is 30-31o C. the cheese left in the press about 24 hours, after which it is removed in order to smooth out all the wrinkles that may be formed on the bandage and to adjust the bandage along the rim at the top and the bottom of the cheese. It then is placed again in the press for another 24 – 48 h.