Defects in process cheese

Whosever takes the trouble to collect samples of processed cheese and processed cheese spreads regularly from the normal marketing sources, and submit them to a thorough organoleptic examination, would soon come, to the conclusion that with the exception of the well known top quality products, many processed cheese products found on the market are exceedingly inferior, with regard to consistency, structure,and flavour. Three well known defects in texture can be established here, “over creaming, stickiness and sandiness”. These defects, which are most certainly of a physico- chemical nature can be observed today more frequently than bacteriological defects, e.g., the dreaded “blowing” of processed cheese due to butyric acid bacilli and other clostridia. With respect to flavour, other objectionable defects include metallic, oily, cardboardy, soapy, bitter and indeed the frequent total absence of the desired characteristic flavour. The causes of these defects can be many: unsuitable raw material, additives of non- standard flavour, unsuitable seasoning, defective dosage and a faulty processing technique. In this connection, poor flavour can occur in the presence of an unsuitably high addition of whey concentrate.

During processing the, the blend thickens progressively with holding time in the cooker. The thickening, frequently referred to as ‘creaming’ or ‘creaming effect’ may be attributed to ongoing interaction of the emulsifying salts with the casein and with the consequent increases in para-casein hydration and degree of emulsification.Both factors contribute to an increase in the apparent viscosity of the molten blend.However, extending the holding time of the molten product at high temperature results in a gradual dehydration of the dispersed sodium para-caseinate, an occurrence which has the effect of imparting elasticity and firmness to the final product.Indeed, prolonged holding results in excessive protein dehydration and aggregation,and a concomitant destabilization of the emulsion, as reflected by the exudation of ‘beads’ of free oil on the surface of the product on cooling. This defect, known as ‘over-creaming’, is also accompanied by a tendency of the product to express some free water in the cooker or on subsequent cooling.

The flavour defects can be overcome by means of extremely careful control during the whole production run. This includes careful selection of raw materials, with regard to flavour and processing properties, the correct use of emulsifying salts and attention to all the features of procedure and critical examination of all finished products.

i. Spoilage of PCPs:

Processed cheese, cheese foods and cheese spreads constitute an important part of the cheese products marketed. Normally they keep satisfactorily because of the heat used in processing, acid and salt present, containers which prevent contamination of the finished products, and perhaps other factors. However, spoilage sometimes may occurs, it may involve microorganisms or chemical changes. Pasteurized processed cheese products are not sterile, as the spore forming bacteria are not destroyed by the heat used. Their growth is controlled by proper pH, salt and Eh level.

Defects in the films used to line boxes or in jar seals may permit the entrance of moulds which find the conditions suitable for growth. Such spoilage usually occurs in only occasional package. Serious spoilage commonly involves heat resistant bacteria which, because of some irregularity grow in the packaged products.Extensive gas blowing may occur in pasteurized processed cheese products. This is caused by Cl. sporogenes and related carbohydrate fermenting bacterial sps., but fortunately, they cause no safety problem. To minimize such an unpleasant occurrence as gas blowing, the basic natural cheese stock should not contain excessive numbers of anaerobic spores, the pH of the finished processed cheese should fall between 5.6 to 5.8, and NaCl content between 2.5 to 3.5(6.0-7.5% NaCl in serum).

The instances of spoilage in process cheese by Cl. Sporogenes has been reported which involved bleaching, development of softened and crumbled areas, and faecal odour, in some areas there was a small dark slit which was considered to be due to gas. The isolation of Cl. Sporogenes and Cl. perfringens from tinned processed cheese which was gassy and had a putrid odour also has been reported. The condition was observed only in cheese in which skim milk powder was added. The same types of organisms were isolated from cheese containing no milk powder, but they did not cause deterioration.

ii. Pinking of Processed Chees

Pinking is a colour defect in processed cheese. This defect is produced by overheating the cheese in the cooker. Its chemical cause is not known, but annatto colour break down during heating may cause this defect. Also in processed cheese containing young natural cheese, the pink colour may result from the Maillard type browning

iii. Browning

In case of processed cheese foods and spreads, the non-cheese dairy products have lactose which causes browning. Bigger the container slower the cooling and more is the browning. Kraft developed a new process to control this problem. The cheese from the cooker runs out and flows on cold water and then strips and pieces of cheese is made.

Storage of Packaged Processed Cheese

The finished, packaged processed cheese should be stored, as far as possible, at temperatures between 5 and 10 °C. Once again it is necessary to emphasized that the processed cheese must not be held at temperatures below 0°C, as freezing can upset its structure. In addition, when the boxes are removed from the cold room,condensation can occur quickly, leading to early spoilage.

When cooling has not been completed, quite often the processed cheese is exposed for a time to temperatures above 20 °C in hot countries as high as 30 °C. This can occur during transport or storage. There is unfortunately a prevailing belief that processed cheese possesses an unlimited keeping quality it often happens that little importance is attached to the storage of processed cheese at higher temperatures.Is processed cheese really absolutely sterile? If a sterilizing process has been used during manufacture, whether by means of a short period ultra high temperature procedure or by means of an autoclave, one can assume that the final product is sterile, so long as a very conscientious and painstakingly clean working operation has been carried out. Unfortunately, the use of a short high temperature processing machine is no guarantee for the production of sterile products. A large number of processing factories still use conventional cookers reaching a temperature between 85 and 95 °C or perhaps slightly higher, so that the possibility of the presence of Clostridia and, in addition, vegetative organisms must always be born into mind.

These organisms, including the Clostridia, will, of course, most certainly continue to multiply and develop with lengthy storage at temperatures around 25-30 °C and eventually cause spoilage and deterioration in the cheese. Therefore, one must avoid storage of processed cheese for long periods at temperatures above 20 °C.Storing sterile processed cheese at higher temperatures is also not advisable because the protein structure and the flavour are detrimentally altered, even though no bacteriological change takes place. In addition, certain defects, which are not evident at normal cold storage, are intensified at temperatures around 30 °C. An example of this is the occurrence of sandiness, which is mostly caused by the formation of fine or course crystals of calcium diphosphate (calcium pyrophosphate). Regular checks are made in most well organized factories by storing representative samples of processed cheese at various temperatures for a certain length of time, e.g., at 10,20,30, and 37°C. From the results obtained after the organoleptic examination of samples stored at 30 and 37 °C, conclusions can be drawn as to possible changes in the products at a later date

Manufacture of processed cheese

The manufacture of PCPs involves the following major steps:

1. Formulation, deciding on the different types and levels of ingredients to be included.

2. Cleaning and comminution of the cheese

3. Blending with ES, water and optional ingredients

4. Processing (heating and shearing) of the blend

5. Homogenization of the molten blend (optional)

6. Hot packing and cooling.

i. Selection of Natural Cheese

Selection is determined chiefly, by type, age, acidity, flavour, body, texture and composition of the lots of cheese available. Some successful operators make their selections entirely on the basis of flavor, body and texture. The proper choice of the cheese must establish uniformly desirable flavor, body, slicing properties and composition. These are attained by mixing many lots of cheese.

In practice any type of cheese without exception can be used. During the entire history of processed cheese there remains scarcely a single type of cheese which has not been investigated. In practice, for economic reasons, factory technique and consistency in quality, cheese which is available in plentiful quantities giving little difficulty in processing and little waste in cleaning is used. The most important types are the hard and semi- hard types, such as, Cheddar, Gouda, Edam, Emmentaler,and Provolone to mention but a few. Due to their relatively high dry matter content and their high intact protein content as structure building matter, they guarantee to the processed cheese the necessary stability. Amongst these types which are easy to process and which cause few complications one can name Cheddar. For this reason,Cheddar is the most widely used type of raw material for processing throughout the world.

It is generally accepted that old cheese alone is not suitable for processing as it results in a cheese having a loose and grainy texture, weak body, poor slicing properties and being liable to fat separation. On the other hand, very young cheese gives a viscous, glutenous mix while young cheese yields a stable emulsion having a smooth texture, firm body and good slicing properties. Old cheese may be blended in with the latter in small amounts to give added flavour to the product. Usually approximately 75% of the blend consists of short held cheese (1-3 months) and the rest consists of cheese 5-6 months old. It has been found that 15% current (tough) cheese may be incorporated in batch taking care to avoid lumps in the finished product, but acid current cheese should not be used as colour defects ranging from straw to deep pink are then likely to occur. Acid cheese should be at least 8 weeks old when used and it is best not to use over 12%. As regard flavour, cheese on the acid side can be an asset. High acid cheese tends to produce grainy texture.

In a successful blending of a batch of cheese for processing it has been suggested that at least three, and often up to a dozen, different kinds of bulk cheese may be required. It was further recommended that the cheese should be of three different stages of ripening:

1. Young cheese 25%, 1-3 month old to impart a cohesive quality to the product.It must not have acid character.

2. Short held cheese 50%, from 3-4 months in age, the cheese must not have rubbery texture, provides mellowness and flavor.

3. Aged cheese- aged 6 months or more- 25% provide flavor.

Thus, it can be seen that young cheese is used for its desirable body texture, and slicing properties and older cheese is used to impart satisfactory flavor. Also, by using a combination of young and old cheese, the average storage time necessary to produce a desired flavor is less than when only medium ripened cheese is used. This practice also caters for the early usage of young cheese of poor curing properties before definite flavour defects are evident.

Many cheese unfit for retailing, i.e. with broken or damaged rinds or cheese invaded by mould after sampling can be salvaged for processing. It has been reported that up to 5% of inferior cheese may be blended with good cheese with no noticeable ill effects, but that putrid cheese should never be used as even 1% in a blend is detectable in the finished product.

ii. Trimming and Grinding

The first step after the cheese has been selected is to trim off all non- edible portions.In processed cheese the trimming is not done as deeply as in case of natural table purpose cheese. This is due to the following:

a) The surface layer is inferior in flavour, and may be unclean, and

b) Beyond this, additional rind may be removed because it is so firm and dry as to be unpalatable.

In processing, only the first of these reasons applies, rind need not be discarded,solely because it is too firm, because grinding and heating will remedy this condition.The rind may be removed by knives. Another method is to soften the rind by tempering.

a) Tempering: Cheese is held in the blending room until it approaches a temperature of 15-21 °C. This may require 48-72 hrs. Warming the cheese in the blending room softens it and facilitates the cleaning, cutting and grinding operations. It has added advantage of reducing the amount of heat required to bring the cheese to its final cooking temperature

b) Trimming: The first step in cleaning is the removal of paraffin and bandage.The first rough cleaning removes most of the soiled areas on the surface of the cheese. The cheeses are then moved to the next area, where all inedible portions of the cheese are scraped of or cut away.

c) Trimming losses: The amount of rind removed from a normal, undamaged cheese is determined by the flavour and consistency of the rind itself. The surface areas of cheese in storage absorbs odours from boxes and storage rooms, the areas affected must be removed in cleaning. A critical operator assumes that any portion of the surface that is not suitable for consumption in its natural state is undesirable for processing. Damaged rinds, cracked surfaces containing mould growth. Mouldy areas surrounding trier holes, spots damaged by box nails and the like are entirely removed. Weight losses in cleaning may range from a few ounces in current cheese to several pounds in an old cheese which may have been damaged by excessive mould growth or other from rind injury. It is minimized by flexible wrapping. The rind can also be softened by exposing the cheese to steam for a short time and then removing the surface by scraping.

iii. Processing

Processing refers to the heat treatment of the blend, indirectly or by direct steam injection, while constantly agitating. Processing has two main functions: 1) to kill any potential pathogenic or spoilage microorganisms, and thereby extend the shelf life of the product; 2) to facilitate physico-chemical and microstructural changes which transform the blend to an end product with the desired characteristics and physico-chemical stability.

The cheese is grinded directly into the cooker. For grinding it is usually necessary to cut the cheese into strips 2-3 inches square. The order of addition of the ingredients varies with plant practices, cooker type, overall plant design, and duration of cooking.A typical order of addition is: ground cheese, a dry blend of emulsifying salts and optional dairy ingredients (e.g. skim milk powder), water and flavours. When the cooking time is relatively short, the ES may be dispersed in a portion of the water added at the beginning of the processing. This approach minimizes the time required for the ES to dissolve during cooking, increases the concentration of ES during early cooking and thereby enhances the effectiveness of the ES in promoting the desired physico-chemical changes in the blend. After the preset time, the remaining water may be added manually, delivered by metering pump, or drawn in by vacuum inside the vessel. Flavours may be added later in the process to minimize the loss of volatile flavour compounds.

Processing may be performed in batch cookers (e.g. Stephan, Damrow) or continuous cookers (e.g. Kombinator, Votator) connected to water, steam and vacuum. During processing, the ground cheese remains crumbly until a temperature of about 49 °C is reached. Beyond this point the cheese becomes sticky, stringy and plastic and may effectively retain (or reincorporate) the fat without the addition of an emulsifying agent. In the early stages of heating there is usually some “oiling off”, especially at temperatures where the fat is fluid and before the plastic condition has been reached, i.e. between 35 and 49°C. If the conditions are correct, this free fat will be reincorporated into the cheese by the stirring at temperatures beyond 49°C. Factors affecting fat separation are 1) age of cheese, 2) acidity, 3) water content, 4) velocity of agitation.

The temperature-time treatment in batch processing varies (e.g.70-95°C for 4-5 min), depending on the formulation, extent of agitation, the desired product texture and shelf-life characteristics. The bacteria in the vegetative state are killed by these temperature treatments. However, a temperature >130 °C may be required to kill some spores. A temperature of 140 °C can be achieved in continuous cookers by virtue of their design, e.g. scraped surface tubular heat exchangers which maximize the surface area of contact between the heating medium (e.g. steam, oil or hot water) and the blend, and ensure sufficient agitation to prevent burn-on of the blend on the heat transfer surface. In continuous cookers, the blend is, typically, heated to 140 °C for 5 s and then cooled to 70-95 °C by flash evaporation of moisture due to a pressure drop, or by passing through scraped –surface tubuler coolers. The product is then held at this temperature for 4-15 min to allow adequate time for interaction of the different blend ingredients, the desired physico-chemical changes to occur and the development of the desired textural characteristics. The blend thickens progressively with holding time at 70-95 °C.

iv. Cooking Technique

The oldest method is heating in a steam jacketed kettle equipped with double action agitators. Steam pressures up to 30lbs/ sq. inch may be used in the jacket. A definite weight of the selected, ground cheese and the calculated and weighed amounts of emulsifying salt and other ingredients are placed in the kettle. The required amount of water and possibly cheese colour are added. Heating and agitation are preferably started before the kettle is completely loaded. The water and emulsifying salts should be present before the heating has progressed very far. The heating and stirring are continued until a temperature of 75 °C is reached. At that stage there should be no free fat and the hot cheese should be semi-fluid with quite a pronounced tendency to draw string. As soon as this condition and the temperature of 75 °C have been reached, the cheese may be discharged from the kettle for packaging. No holding is necessary for the sake of pasteurization, since the packaged product will cool slowly and will be within an effective pasteurizing range for some time.

v. Packaging

The cheese is packed as soon as possible after heating to avoid aerial contamination.It has been reported that 18-21° C is the best temperature for the cooling room,the packages should not be placed under refrigeration until they have attained these temperatures.

The main requirements for packaging materials for process cheese are:

1) moisture retention,

2) impermeability to oxygen,

3) no off-flavour side effects, and

4) close adherence to the cheese

The following packaging materials were tried: tin, tin foil, cellulose films, glassine, coated aluminium foil and laminates of aluminium foil and parchment paper. It has been reported that tins and parchment paper impregnated with foil are the best.

Ingrediants used other then cheese in pasteurized processed

Ingredients, other than cheese used in pasteurized processed

cheese products

Definition and composition of process

There are various types of PCPs, the type or category of which, and standards of identity therefore, depend on the particular region where they are produced. In the United States, the code of Federal Regulations defines four types of PCPs based on permitted ingredients and composition (Table). The percentage of natural cheese in PCPs ranges from a minimum of 51% in pasteurized processed cheese spreads and foods to 95% in pasteurized processed cheese.

                                              Ingredient and compositional specifications for pasteurized

processed cheese products
According to PFA standard Processed cheese means the product obtained by heating cheese with permitted emulsifiers and / or stabilizers namely, citric acid, sodium citrate, sodium salts of orthophosphoric acid and polyphosphoric acid (as linear phosphate) with or without added condiments and acidifying agents, namely vinegar,lactic acid, acetic acid, citric acid and phosphoric acid, processed cheese may contain not more than 4.0 percent of anhydrous permitted emulsifiers and/ or stabilizers,provided that the content of anhydrous inorganic agents shall in no case exceed 3.0 per cent of the finished product. It shall not contain more than 47.0 per cent moisture.The milk fat content shall not be less than 40.0 per cent of the dry matter. Processed cheese may contain 0.1 per cent sorbic acid or its sodium, potassium or calcium salts (calculated as sorbic acid) or 0.1 per cent of nisin either singly or in combination.It may contain calcium chloride (anhydrous) not exceeding 0.02 percent by weight.

Principle and Methods of Manufacture of Pasteurized Processed Cheese Produ cts(PCPS)

Pasteurized processed cheese products (PCPs) are cheese-based foods produced by comminuting, blending and melting one or more natural cheeses and optional ingredients into a smooth homogeneous blend with the aid of heat, mechanical shear and (usually) emulsifying salts (ES). Optional ingredients which are determined by the product type, include dairy ingredients, vegetables, meats, stabilizers, emulsifying salts, flavours, colours, preservatives and water (Table ).

Attempts to increase the shelf life of cheese during the early twentieth century were inspired by the possibility of increased cheese trade, via the production of more stable transportable products, and by the existence of heated cheese dishes such as Swiss fondue and Kochkase. Many of the early approaches were unsuccessful, as the heat treated cheese were unstable, as reflected by oiling off and moisture exudation during cooling and storage. In 1911, the Swiss workers Gerber and Stettler produced a stable, heat-treated stable Emmental cheese, known as Schachtelkase, by the addition of a ‘melting salt’, sodium citrate, to the commuted cheese before processing (i.e. heating and shearing). Subsequently it was found that other cheeses (e.g. Cheddar) could also be processed to form stable products by the addition of other ‘melting salts’ (e.g. sodium phosphates) or blends of different emulsifying salts. The ‘melting salts’ were gradually referred to as emulsifying salts when their functions became known, i. e. mediation of the processes of protein hydration and emulsification of free fat during processing. Initial successes were followed by numerous patents for different melting salt blends and later for inclusion of food ingredients other than cheese.

The basic aim of processing is to blend natural cheese, water, optional ingredients and emulsifying salts and to pasteurize the mixture to obtain an end product which has sufficient fluidity for convenient packaging and which possesses long keeping qualities. It is believed that the popularity of processed cheese products is based on its uniformity, mildness and good keeping quality.

In the year 2003, global production of PCPs is estimated at~1.5-1.8 MT per year,equal to ~ 10-12% of natural cheese production. Moreover, production has been steadily increasing at a rate comparable to that of natural cheese; indeed, the mean annual growth rate (1.4%) in the 15 countries of the EU for the period 1995-99 was greater than that (0.6%) for natural cheese. Factors contributing to the continued growth of the PCPs include:

•  the application of heat during processing stabilizes the cheese system into a physico-chemically and bacteriologically stable state enhancing the shelf life of the product. This ensures conservation of precious milk solids during glut period into a valuable form of process cheese. This product can be stored for months or even years.
•  their versatility as foods that offer wide variety in flavour, texture (e.g. elasticity, firmness, spreadability, sliceability), cooking attributes (e.g. degrees of flowability, browning, viscosity), size and shape of final product, and overall consumer appeal as made possible by differences in formulation and processing conditions, condiment addition and packaging technology.their convenience of use in the food service sector, especially the fast food trade, and the home because of their excellent (stability) preservation, consistent tailormade
•  functionality (e.g. flowability), convenient portion size and packaging (e.g. as slices for the beef burger and sandwiches trade)
• their popularity with children of different ages owing to their safe ingestable consistency (for infants) and mild flavours, and their packaging (colour, caricatures, strength, ease of opening, size) and shape (e.g. triangles, fingers,cartoon characters).
•  their nutritive value (e.g. as a source of calcium and protein) as a food for children. Because of its digestibility and beneficial properties processed cheese is suitable as a diet food.
•  their relatively low cost compared to most natural cheeses, made possible by the use of relatively cheap non-cheese solids (e.g. whey, skim milk powder),lower-grade natural cheese, and offcuts.
•  Manufacture of process cheese with the addition of other food types (meat,sea-foods, mushrooms, vegetables, fruits, fruit juices, dietetic substances and vitamins.
•  Manufacture of dried cheese from plain or seasoned processed cheese to be used for sprinkling on soups, pasta or to be reconverted into spread by the addition of water.
•  Manufacture of dried cheese from plain or seasoned processed cheese for the preparation of bakery goods, e.g. cheese flavoured biscuits.
•  developments in manufacturing technology, emulsifying salt blends and functional dairy ingredients which facilitate the manufacture of consistent quality products with customized attributes.

Use of milk of other species

Mozzarella cheese was traditionally manufactured from buffalo milk in Italy, where it originated. The technology has hence been modified for cow milk and is being used widely all over Europe and U.S.A. Under Indian conditions, the milk that finds its way to the processing sector is of the mixed type, the major share being buffalo milk and the rest, cow and goat milk.

An average Indian farmer keeps buffalo, cow and goat for different agricultural purposes and hence, the milk that he produces is generally a mixture of a large quantity from one species of animal mixed with smaller quantities from other species. It is thus, essential to study the effect of blending of two milk systems. As such buffalo milk is unsuitable for the manufacture of Cheddar type and soft cheeses, as it results in hard, crumbly, coarse and brittle body and texture defects, whereas goat milk curd being soft, is unsuitable for making hard cheeses. Thus, blending these two milks would result in a Mozzarella cheese of most desirable characteristics. It has been reported that blending of buffalo and goat milk in 1:1 ratio results in good product. The mixed milk should contain a fat content of 3 % to result in satisfactory product. The organoleptic qualities, grating, melting and baking characteristics and eating quality of the cheese on Pizza was adjudged to be very good.

The rennet coagulation was faster in buffalo milk due to much faster rate of secondary action with high calcium. The buffalo milk curd was always firmer and stronger than cow milk curd of the same solid content. Goat milk had a shorter rennet coagulation time than in cow milk

Defects in Cheese

A smooth surface with a perfect sheen is the desired quality in good Mozzarella cheese. Some of the defects reported in Mozzarella cheese are poor meltability,discolouration, putrid smell, bitter taste and abnormal texture.

Traditional fresh Mozzarella and low moisture Mozzarella produced as string cheese or pizza cheese should have a very delicate flavour originating exclusively from the lactic fermentation by the starter culture. Because the flavour is very mild, other flavour notes are readily detected at low intensities and are generally considered defects. The most common flavour defects in cheeses are bitterness and high acid(sour), but rancid or unclean flavours can occur if poor-quality milk is used.

Textural defects are particularly problematical in pizza cheese because the quality of pizza cheese is defined largely by shredding and melting properties. Pizza cheese with a soft body due to high fat or moisture content, low calcium content, or excessive proteolysis may gum up the shredding equipment and take longer to process through the equipment. The resulting cheese shreds may be deformed in shape, sticky and prone to matting. When melted, such cheese may flow excessively (soupy) and lack stretch, elasticity and chewiness. At the other extreme, pizza cheese with an abnormally firm body due to low moisture or fat content may also take longer to shred and shatter and form fines during shredding. Such cheese may melt to a very tough and elastic consistency that is overly chewy. It may also blister excessively on pizza. Blisters occur when stable bubbles are formed at the cheese surface during baking, resulting in dehydration and the formation of a dried skin at the top pf the bubble. Cheese that melts to a tough, fibrous consistency will tend to form more stable bubbles and be more prone to blister formation than cheese that is less fibrous and elastic when melted. Non -enzymatic browning reactions involving reducing sugars (lactose or galactose) and amine groups (mostly from peptides and amino acids) may occur readily at the blister site and may give rise to brown or in extreme cases, black patches.

Either excessive or inadequate release of free oil from pizza cheese during melting represents important defect for pizza cheese. Excessive release of free oil results in unattractive greasy pools of oil at the surface of the pizza, whereas inadequate free oil release can lead to poor meltability, widespread skin formation and scorching at the melted cheese surface.

Packaging

The packaging of cheese is particularly important for the shelf life of the product.The basic requirements for the cheese packaging are (i) exclusion of oxygen to prevent mould growth and rancidity , and (ii) retention of moisture to preserve the texture and avoid weight losses.

In general, the higher the moisture content of the cheese, the more likely it is to spoil on storage. Since Mozzarella cheese contains high moisture (about 50%) it is very susceptible to spoilage from yeasts and moulds and is usually packed with vacuum in polyethylene.

It has been reported that the spoilage of Mozzarella is mainly caused by the mould growth because of high initial count and absence of natural inhibitors such as propionic acid. Vacuum packaging helped to reduce the increase of mould in packaged cheese but with sliced Mozzarella a high vacuum of 29 inches must be maintained for effective control.

Irregular shaped Mozzarella cheese is generally packaged in flexible roll films, thermoformable packets or shrinkable pouches like cryovac. Mozzarella loaves are wrapped with multiplayer heat shrink bags of vinyledene chloride such as cryovac S type. The bags are evacuated and heat shrunk to give a desirable tightness.

After brining the cheese should be dried briefly and wrapped in parchment, saran or vacuum packed in cryovac, polyethylene or cellophane pouches followed by storage at refrigeration temperature.

Chemistry of “Stretch” of Mozzarella Cheese

The development of curd stretch is governed by the amount of calcium that is available for casein crosslinking. The key to producing pasta-filata cheese is to attain simultaneously the appropriate moisture content in the curd at the time of stretching and the level of casein-associated calcium that is necessary for the curd to stretch in hot water or brine. Curd that contains too much casein-associated calcium will tear and fracture during stretching and fail to attain a plastic, stretchable consistency. On the other hand, too little casein- associated calcium results in complete loss of structure and stretch when the curd is worked in hot water.Both the total calcium content of curd and the distribution of total calcium between the casein associated and soluble states determine the amount of casein-associated calcium at the time of stretching. Total calcium content depends on the amount of calcium that is lost to the whey when acid is produced by the starter during cheese making. Calcium distribution, on the other hand, is governed by the curd pH at the time of stretching: a low pH favours calcium in the soluble state while a high pH favours calcium in the casein-associated state. Therefore, controlled acidification, demineralization and dehydration, coupled with attaining a critical curd pH at the time of stretching, are the key technological parameters for all pasta-filata cheeses.

In the calcium rich environment of milk, the casein precipitates out of milk as dicalcium paracaseinate, entrapping fat, insoluble minerals and some sugar. At a pH between 5.2-5.4, resulting from the development of acidity, some of the calcium of the dicalcium paracaseinate gets dissolved, leading to the formation of monocalcium paracaseinate.This when heated to 54 °C or higher becomes smooth, pliable and stringy and retain fat. If acidification is excessive, generally below pH 5.2, monocalcium paracaseinate will continue to lose calcium and form paracaseinate, which may stretch, but has difficulty in retaining fat. The curd generally does not stretch above pH 5.6.

Method of manufacture of Mozzarella cheese by direct acidification

The method of manufacture of Mozzarella cheese by direct acidification involves the lowering of pH by different acids. This technique helps (i) to eliminate variability of acid production by bacteria, (ii) to avoid problems created by bacteriophages, slow starters and other contaminants (iii) to have better control over pH variations and (iv) to reduce manufacturing times.

It has been reported that a 2 % milk acidified to pH 5.6 at 4 °C with acetic, lactic and hydrochloric acids resulted in satisfactory product. Calcium levels and recovery of solids- not- fat were higher in pizza cheese made with phosphoric acid than those with hydrochloric and lactic acids. Cheeses made with phosphoric and hydrochloric acids had lower moisture content and were firmer than cheese made with lactic acid. However the type of acid had no effect on fat recovery. The manufacturing steps are shown in Flow diagram .

Method of manufacture of Mozzarella cheese from buffalo milk using starter culture

The basic manufacturing technology for Mozzarella cheeses is similar to that of Cheddar cheese with slight variation. The standardized (4% fat) and pasteurized buffalo milk is put in cheese vat. The starter culture containing S. thermophilus and L. bulgaricus (1:1) is added to milk at 31-35°C @ 2%. After ripening for about 50 min the rennet is added @ 1.0 g / 100 lit. After about 30 min the curd is set which is cut and allowed to stand in the whey for 10-15 min. The curd is cooked gradually by increasing the temperature to 40-41 ° C in 30-35 min. The whey is drained and the curd is allowed to ripen to an acidity level of 0.75-0.80 %. At this stage the curd is immersed into the hot water (80-85 °C). After about 2-3 min the curd is kneaded, stretched and moulded normally for proper body and texture development. The moulded cheese is dipped into chilled water (5-10 °C) for cooling for 1-12 h. The cheese is then transferred to brine of 20% concentration at refrigeration temperature (8-10 °C) for salting. The pH of the brine solution is kept at 7.6. After the cheese attains the desired level of salt (1.6-1.8%) it is taken out and dried in a cold store. The cheese is then packaged and disposed off. The manufacturing steps are shown in flow diagram .

Manufacturing Steps (Traditional Method)

Principle and Methods of Manufacture of Mozzarella Cheese

The Mozzarella cheese was originally manufactured from high fat buffalo milk in Italy. Now in European countries and U.S.A. it is also being made from cow milk.It belongs to the cheese classified as “pasta filata” which involves the principle of skillfully stretching the curd in hot water to get a smooth texture and grain in cheese.It is a soft, white, unripened cheese which may be consumed shortly after manufacture.Its melting and stretching characteristics are highly appreciated in the preparation of Pizza where it is a key ingredient.

Production of Mozzarella cheese far exceeds that of all other cheeses of pasta-filata  cheese because Mozzarella is an essential ingredient of pizza. Pizza, like Mozzarella,originated in Italy and spread through communities of Italian immigrants in other countries, until the middle of the twentieth century. After World War II, however,pizza restaurants in the U.S. began to establish market outside the traditional ethnic communities. By the mid-1970s, pizza was firmly established as a popular food with broad appeal in the U.S. The development of fast food and franchise chain pizza restaurants further hastened the growth of pizza, which eventually became an omnipresent element of American culture. Along with the growth of pizza came an unprecedented increase in the demand for Mozzarella cheese, as evidenced by striking increase in U.S. production of Mozzarella over the past 25 years (Fig ).

More recently, American franchise restaurant chains have expanded aggressively in other countries, thereby increasing the popularity of pizza in Europe, South America and Asia. As a result, worldwide demand for Mozzarella has skyrocketed, and many countries, in addition to the United States and Italy, now produce sizeable amounts of Mozzarella cheese, including Argentina, Australia, Brazil, Canada, France,Ireland, The United Kingdom and New Zealand.

Buffalo milk Cheddar cheese

Cheddar cheese is manufactured mainly from cow milk in major cheese producing countries. However, in India the major share of milk production is from buffaloes.The adaptation of well known technology for the production of various products from buffalo milk posed many problems, primarily because of its qualitative and quantitative differences. The main problems encountered in the manufacture of hard type cheese from buffalo milk have been faster renneting, lower retention of moisture,slower lipolysis and poor proteolysis and poor flavour and body texture development.

The buffalo milk cheese is criticized for being flat and hard, rubbery and dry body and texture.The defects in buffalo milk Cheddar cheese are attributed to the physio-chemical and compositional characteristics of milk. The high buffering capacity of buffalo milk due to higher calcium and casein content is the cause for slower development of acidity. Faster renneting time may be attributed to its higher colloidal calcium content (about 160 mg/ 100 ml compared to only 80 mg/100 ml of cow milk). Lower retention of moisture in the curd may be the result of low hydration of its casein compared to cow milk casein. Hard, rubbery and dry body may be due to high curd tension which, in turn, is the result of higher content of casein with bigger size of the micelle, high content of calcium and magnesium more so in the colloidal state,larger proportion of solid fat with bigger size of the globules and low voluminosity and solvation of its casein micelles compared to the same in cow milk. Slower rate of proteolysis and lipolysis is the cause of higher curd tension of buffalo milk.

Recently the technology for the manufacture of buffalo milk Cheddar cheese has been standardized by employing the following process modifications:

•  Using relatively higher heat treatment for pasteurization of cheese milk (69 °C / 30 min.).
•  Addition of starter culture at higher level (2%).
•  Using starter adjuncts such as Lactobacillus casei or L. helveticus (0.5%).
•  Setting rennetted milk at lower temperature (28 °C).
•  Reducing temperature and duration of cooking (37 °C/40 min.).
•  Frequent turning of blocks during cheddaring.
•  Applying relatively mild pressure.
•  For accelerated ripening- use of enzymic preparations such as Flavorage, Naturage, accelase, etc. may be made.

Defects

Defects in Cheddar cheese arise through contamination of milk with undesirable microorganisms, inadequate acidification during manufacture to attain the optimum compositional factors of pH, salt and moisture. Additionally, physical damage to packaging of vacuum-packed Cheddar can allow the contamination and growth of undesirable microorganisms on the surface of the cheese.

The defects in Cheddar may relate to flavour, body & texture, colour or appearance.Flavour defects may be bitter, acid, fruity, unclean,rancid, etc. The defects in body and texture could be corky, curdy,crumbly, mealy,pasty, short body and gassy and open texture. The colour defect may be acid-cut, bleached discolouration and seamy etc.

i. Flavour

i) Bitterness: Bitterness in Cheddar is associated with the accumulation of hydrophobic peptides which are formed by the action of the coagulants and starter proteinases. Bitter peptides are derived from both ás- and â- caseins.Chymosin is important in the production of bitter peptides, since residual coagulant in Cheddar releases extreamely hydrophobic peptides from â- casein. Cutting the coagulum at low pH in Cheddar manufacture results in the retention of excessive chymosin and the development of bitterness. A low salt content in final cheese will enhance chymosin activity and result in the accumulation of bitter peptides. The overall level of bitterness in Cheddar will depend on the relative rates at which bitter peptides are formed and degraded to nonbitter peptides. Certain Lc. lactis strains are associated with the development of bitterness in Cheddar cheese. These strains survive well at the scald temperature used in Cheddar manufacture and their presence at high numbers in the fresh curd results in high proteolytic activity during ripening. The total proteolytic activity of the starter strains can have a significant effect on the development of bitterness.

ii) Fermented: Fermented flavours are characteristics of the odour of fermented whey. They possess some of the qualities of the combined odours of alcohol,acetic acid and propionic acid. They may appear in cheese soon after it is made, but they usually develop after the cheese is two weeks of age. They are believed to be caused by yeasts or bacteria. These organisms may get into the milk on the farms by contact with unclean and non-sterile surface of utensils,milking machines and milk cans. The occurrence of this flavour defect can be prevented by taking utmost precaution in plant sanitation, by using clean and active starter and ripening the cheese at or below 8°C.

iii) Fruity: Fruity flavours resemble that of ripe fruits such as pine-apple, raspberry etc. These are closely related to the fermented flavour defect. Hence the origin, prevention and remedies may be considered identical to that of fermented.

ii. Body

The term body is used in the cheese industry to designate the physical properties of consistency. These properties include firmness, cohesiveness, elasticity and plasticity.These physical characteristics of cheese are sometimes called rheological properties.Firmness is the property of the cheese which causes it to resist deformation or distortion under pressure. Cohesiveness is the characteristic of the cheese that causes it to stick together. Elasticity is the capability of the cheese to recover its size and shape after deformation. Plasticity is the quality of the cheese which enables it to be deformed under pressure without rupture.

The rheological properties of cheese are affected by methods of manufacture and composition of cheese. Various terms are used to indicate the firmness, elasticity,cohesiveness and plasticity of curd and cheese. These terms describe the appearance and the feeling of the cheese when a plug is removed from the cheese block. A normal plug of ripened Cheddar shows a smooth, uniform surface. It feels solid and firm, it does not crumble when cut or pressed. It bends before breaking and when rubbed between the thumb and fingers, it feels smooth and waxy like cold butter.Some of the common defects are as follows:

i) Corky Body: Cheese with a firm, hard, tough and somewhat elastic consistency is called corky. Such cheese is difficult to crush with the fingers, but when enough pressure is applied it breaks apart in a woody manner. Corky body may be apparent as very firm curd at the time of draining, the characteristics usually appear before salting. Corky characteristics may persist throughout the life of the cheese. This defect may be caused due to low fat content, lack of acid development, overheating during cooking, lack of moisture and excessive salt content.

ii) Crumbly Body: Crumbly body is characterized by the falling apart of cheese when sliced, by difficulty in removing a plug and by the breaking of the cheese into pieces crumbs when crushed between the thumb and fingers. This lack of cohesion is apparent through the whole cheese, it is not limited to surfaces of the curd particles which make up the cheese Crumbly cheese usually feels firm before breaking. It shatters with snap like breaking of chalk.

iii) Curdy Body: Curdy body is natural in fresh cheese, it is rightly regarded as a defect only when persists beyond about 30 days. Curdy cheese when broken apart reveals the size and shape of the original curd particles after salting. When pressed in the finger it feels elastic, firm and somewhat like the particles of the curd at the time of salting. It can not be worked together in the fingers after it has once been broken apart.It may be caused by low moisture content which delays curing, lack of proper acid development, lack of proper cheddaring in the vat before milling, addition of excessive amount of salt or low temperature storage.

iv) Mealy Body: This characteristic appears when cheese is crushed and rubbed between the thumb and fingers ,the structure of the curd looks and feels rough.The characteristic is the opposite of the waxy, smooth desired in normal cheese.Mealy body can be most readily detected after the curdy characteristics of the cheese have been fully disappeared, it is actually apparent during the first week of curing but is not so easily discovered. It persists throughout the life of cheese.It is mainly caused by excessive acidity. It may be regarded as a stage of disintegration of crumbly cheese. Mealy body in cheese can be eliminated in future lots by observing the preventions and remedies for excessive acidity.

v) Pasty: Cheese with pasty body is soft in consistency when pressed and rubbed between the fingers, it quickly becomes sticky and clings to the fingers. Pasty body in cheese becomes apparent as soon as the curdy characteristics disappear. The defect is caused by excessive moisture.

 iii Texture

Texture is the term used to describe the manner of union of the particles of cheese.If there are few openings or none at all between the particles, then the texture is said to be close or solid. If there are spaces between the particles or if there are voids or openings in the body, then the texture is said to be open.

i) Gas Production: Open texture and slits in Cheddar have been attributed to the growth of obligate and facultative heterofermentative lactobacilli.Fermentation of residual lactose and galactose, resulting in the production of CO2, is associated with this defect. Slow starter activity and a high level of residual lactose in the curd are the main causes. Late gas-blowing in Cheddar is associated with contamination of the cheese milk with Clostridium tyrobutyricum.

ii) Colour defects: Colour plays an important role in the consumer acceptability of Cheddar and can influence grading. Bleaching of Cheddar is sometimes observed shortly after manufacture. Localized areas of high acid production with whey entrapment between curd particles can cause bleaching during the early stages of maturation. This effect diminishes as the cheese matures and the pH increases. Colour defects ranging from pink to mud-brown have been observed sporadically in both annatto-coloured and white mature Cheddar.

iii) Mould Growth: Most commercially produced Cheddar is vacuum-packaged and as moulds require oxygen to grow and sporulate, they are found where pockets of air exists between the cheese surface and packaging. Growth is limited by the amount of limited oxygen.

Ripening

Flavour and texture in Cheddar cheese develops over extended maturation period. Proteolysis is the most extensive biochemical event occurring during ripening and, in contrast, lipolysis is limited. In mature Cheddar, approximately 25% of the total nitrogen is soluble in water and small peptides and amino acids, which contribute to flavour, generally participate into this fraction.

The starter lactic acid bacteria make a significant contribution to cheese proteolysis.The proteolytic activity of the NSLAB supplements that of starter producing peptides with similar molecular weights to those produced by the starter culture and also amino acids.

i. Amino Acid Catabolism: The free amino acids generated as a result of proteolysis may be catabolized by the starter lactic acid bacteria and NSLAB to flavourful compounds such as aldehydes, alcohols, esters and thiols. As the final flavour of cheese depends on the respective concentration of different key aroma compounds, the control of amino acid degradation during cheese ripening appears to be a potential means of manipulating the flavour profile of Cheddar.

ii. Textural Characteristics: Freshly pressed Cheddar cheese comprises a casein matrix interspersed with fat globules and water. The cheddaring process leads to the formation of a fibrous protein network that produces a very close – textured Cheddar cheese. The relative levels of fat, protein and moisture affect the rheological properties of the curd and the rate of texture development is associated with the degradation of the casein. Within the first 7-14 days,residual coagulant enzymes are responsible for the rapid hydrolysis of the ás1- casein to soluble peptides and this causes mellowing of the rubbery elastic texture.

iii. Taste and Aroma: Cheddar flavour is not associated with one potent chemical compound but appears to result from the generation of number of components during ripening. The production of cheese flavour compounds must be balanced and excessive production of individual components leads to generation of offflavours.The taste of Cheddar is associated with the water-soluble nonvolatile fraction.This is comprised of small and medium-sized peptides, free amino acids, organic acids and their salts. Peptides and amino acids contribute to the background savoury flavour of Cheddar, while specific peptides can impart undesirable bitter flavours. Volatile aroma compounds have the potential to add the specific flavour notes to Cheddar. These are mainly derived from proteolysis but also from lipolysis.

Packaging

Cheese packaging can be broadly grouped as (1) Protecting the cheese for storage and ripening and (2) Packaging for consumers. Cheese is normally covered with a protective coating at some stage of the ripening process. Coating varies from vegetable oils to special plastic films. The shape and characteristics of cheese and changes to be induced in cheese dictate the type of packaging material. The objective of such treatments are: 1) general protection, 2) assistance in forming the coat or rind, 3) improvement of appearance, and 4) prevention of loss of moisture, and specific protection against external microorganisms and insects.

i. Paraffining: The Cheddar cheese is removed from the press and placed in a cool, dry place for several days to permit the surface to dry. After a dry surface is secured the cheese is dipped into a vat of paraffin which has previously been heated to 100- 115o C for about 5 seconds. This procedure covers the cheese with a thin layer of paraffin, closes all pores, kills any mould that may have grown on the surface and checks evaporation of the water from the cheese during curing.The most suitable storage temperature for waxed cheese is 8-10o C but if quicker ripening is desired, a temperature not exceeding 12o C may be used.For slower ripening a temperature of 7o C is suitable.

ii. Wrapping: The most significant change in packaging of cheese prior to ripening was the development of rindless block style of cheese. The cheese is pressed in rectangular hoops or forms and wrapped in plastic film. The films are usually laminants of different plastic films and waxes with specific properties. This system of packaging has several advantages. It is not necessary to dry the cheese surface as thoroughly as is done in waxing of cheese which eliminates yield loss. Ripening of film wrapped cheese can be done at lower humidity levels without excessive moisture losses from the cheese.