Processed Cheese

Introduction To Processed Cheese

Processed cheeses or process cheese as its sometimes called (PCP) are composite dairy foods which are to all intents and purposes reconstructed cheese products. They must use natural cheese but can include a variety of other ingredients, most notably unfermented dairy ingredients and various added but defined emulsifiers. 

Many types of process cheese can be produced based on the types of cheese used, the level and variety of flavouring and the clever use of emulsifying salts, all together generating a variety of different textures. The most common emulsifying salts are sodium salts of phosphates, polyphosphates and citrates (Guinee et al., 2004).

Unlike natural cheese, process cheese is entirely manufactured without the need for ‘fermentation’. The most common production method for processed cheese involves forming a cheese matrix under a partial vacuum, with constant stirring and agitation, and with heating. It is also homogeneous and is produced in various forms such as blocks, slices, shreds and sauces.

Process cheese is the ideal material as a melting cheese because of the types of ingredient it contains. The traditional cheese for melting contains mainly milk proteins  such as casein fractions or their partial hydrolysates, dairy fat and water. It is not as effective as process cheese in this type of processing.

Processed cheese is also a pasteurised product. 

This cheese can also be subdivided into cheese types such as analogue cheeses which are used on pizza toppings as well as conventional processed cheeses. We might also hear it called prepared cheese or cheese food.

It continues to increase in popularity because of its versatility and the wide range of types that are possible. In the USA, ‘American Cheese’ is the most popular form and has come to define a smooth and very mild flavoured cheese. as well as slices such as the Kraft Slice, the cheese can be sprayed more added convenience.

History

Processed cheese began life as early as the late 1800s in Europe although 1911 is accepted as the true start for this particular food. It was first made that year in Thun, Switzerland, by Walter Gerber and Fritz Stettler of Gerber and Co.  who melted Swiss cheese using sodium citrate as the emulsifying salt to produce a smooth, homogeneous product.

These cheeses were constructed with improved shelf-life compared to natural cheese. They also had a more uniform flavour and appearance, and were easier to pack. Such cheese was also ideal for cooking with because of their better melting capability.

One of the other benefits of processed cheese was that viscous, rather plastic spreads were possible without having to resort to sauces. They were also found to be very mild in flavour but could be bolstered by the addition of other flavours to create exciting new ranges. 

A few years later, in the United States, the development of process cheese was brought about by J. L. Kraft in 1916, when he preserved natural cheese in cans by heating and mixing it in order to increase its shelf life. It was then in the 1920s in the USA that processed cheese truly began to take shape. 

The development of process cheese as we know it today using  phosphate‐based emulsifying salts in the United States is attributed to J. L. Kraft and the workers from the Phenix Cheese Co. The latter business developed the famous Philadelphia cream cheese product. Kraft acquired this business in 1928. Over those years, Kraft were awarded numerous patents for their work on process cheese between 1916 and 1938.  The Kraft Singles was introduced in 1947 and is now the most often bought type of cheese in the USA.

Process cheese can as was later found use reformed and waste natural cheese which might not be acceptable in other quarters.  

Regulations On Processed Cheeses

In the United States, process cheese is a generic term used to describe various categories of cheese as defined by the Code of Federal Regulations (CFR). According to the CFR, these categories differ on the basis of the requirements for minimum fat content, maximum moisture content, and minimum final pH, as well as the quantity and the number of optional ingredients that can be used (21CFR133.169 to 133.180) (FDA 2006).

The 3 major categories of process cheese, as described by the CFR, are pasteurized process cheese (PC), pasteurized process cheese food (PCF), and pasteurized process cheese spread (PCS).

A pasteurised process cheese (PC) contains natural cheese. This may be a mix of cheeses and by composition contains less moisture but more fat than a process cheese food (PCF). It will have added emulsifiers, salt and some other ingredients like colouring. The moisture and fat contents are the same as the legal limits for natural cheese. The moisture content must be at least 45%.

By law, the FDA in the USA states that processed cheese food must contain at least 51% natural aged cheese by weight. The non-dairy ingredients should not exceed one sixth of the total weight of solids on a dry matter basis. This is the process cheese we are most familiar with. The moisture content should not exceed 44% and the fat content should not be less than 23%.

A processed cheese food contains natural cheese, emulsifiers, sodium chloride and colour as for a processed cheese. It can also contain milk, skim milk, whey, cream and organic acids. 

The Code of Federal Regulations (CFR) also states 13 types of emulsifying salts that can be used in process cheese manufacture, either singly or in combination, and allows for the addition of up to 3% (wt/wt) (Kapoor & Metzger, 2008).

In labelling terms, processed cheese cannot be sold as ‘cheese’ but must be called by legal definition ‘cheese food’. For extra sophistication, the products can be labelled based on the natural cheese used, their moisture content and level of milk fat.

Processed Cheese Spreads (PCSs)

Processed cheese spreads (PCSs) are the 3rd category of products according to the FDA. They are prepared by melting one or multiple types of natural cheeses with emulsifying salts to form a homogenous product with improved shelf-life (Kapoor and Metzger, 2008).They are obtained as for process cheeses which are designed primarily for spreading. They retain a paste like quality.

In regulatory terms, a processed cheese spread has a maximum moisture content of 60%w/w, but no less than 44%, but similar milk fat and lactose levels to a typical processed cheese. Gums can be added here to aid spreadability.

Ingredients

The most important ingredients (as we have already mentioned) are natural cheese and the emulsifying salts. Natural cheese makes up at least 51% of the product (FDA, 2006) in processed cheese. Other ingredients including the emulsifiers make up the remaining 49% by weight of the product.

It is usual to find most cheese analogs prepared from caseinate alone or as the main protein source.

Considerable work has been undertaken in the last 100 years on understanding the physical and chemical changes that occur to process cheese during its shelf-life and the impact of so many ingredients on sensory quality.

The added ingredients include water, vegetable oil, cream, whey protein, dried whey, dried skim milks,  butter oil,  casein and casemates, salt, spices and flavourings, food colouring, preservatives, lactose, organic acids, hydrocolloids and in some instances sugar. Developers can also use milk as well as skim milk.

Ingredients: Natural Cheeses

Natural cheese is the most important ingredient in processed cheese. In the USA, cheddar cheese is most often used. The amount of natural cheese used will most likely dictate the type of process cheese to be manufactured. A typical formula will vary from between 51 to about 85%w/w. Most of the cheddar produced in the USA is used for process cheese manufacture although Colby cheese is also highly sought after.

The characteristics of natural cheese used in manufacturing process cheese have a major influence on its functional properties. It will dictate its unmelted texture and melting properties. It was known from relatively early on that understanding how natural cheese behaved in any formula was essential for commercial success (Barker, 1947).

Cheese spreads have been prepared using cheddar, Dariworld (a soft ripened cheese of little flavour) and Nuworld (mould-ripened, strong flavoured cheese). The use of the latter types of cheese were claimed to give superior spreadability. 

Cheese acidity is important in texture. Incorporating some cheese with slight acidity is beneficial in achieving the most desirable texture. Cheese which has a high titrateable acidity produces a soft spread (Davel & Retief, 1928). 

Ingredients: The Role of pH

 One of the most important factors affecting the properties of processed cheese is pH. It has been studied for many years (Templeton & Sommer, 1932; Marchesseau et al., 1997; Lee and Klostermeyer, 2001).

It was Templeton and Sommer who first formally reported that cheese texture was a function of pH. If the pH was below 5.2 then the manufactured cheese was dry, crumbly and mealy with a ‘low’ hardness. When the pH was above 6.4, the cheese was just too soft. When the pH changes from 6.2 to 5.0, the hardness and elasticity rises (Stampanoni & Noble, 1991).  .

Ingredients: Emulsifiers In Process Cheese

Emulsifying salts are essential in the formation of a uniform (homogenous) structure of any processed cheese. These are added at a level of 1–3% w/w. The basic function is to improve hydration in the cheese structure and the partial dispersion of calcium-parcaseinate phosphate networks (Chen & Liu, 2012).

One of the consequences of adding emulsifying salts is a shift in the pH to a more alkaline level usually from 5.0 to 5.5 in natural cheese to 5.6 to 5.9 in a processed cheese. The pH change relates to the type of emulsifying salts used, their pH in solution, their buffering capacity and the degree of buffering within the cheese.

The most extensively used emulsifiers are the sodium phosphates and trisodium citrate. These emulsifiers act by sequestering calcium and by adjusting the pH in the process. This in turn means they control texture, melting properties and the amount of free oil formation. Their impact is best explained in terms of casein behaviour in the cheese matrix (Caric et al., 1985).

Incidentally, these emulsifiers are not strictly real emulsifiers like mono- and diglycerides. They are not surface-active ingredients.

The key properties of the emulsifiers are:-

(1) disodium orthophosphate (DSP), Na2HPO4.2H2O, MW = 178, pH of 1% (w/w) solution in water = 9.1, solubility at
20 ◦C = 80 g/100 g H2O;

(2) trisodium citrate (TSC), Na3C6H5O7.2H2O, MW = 294, pH of 1% (w/w) solution in water = 8.6, solubility
at 20 ◦C = 75 g/100 g H2O;

(3) tetrasodium pyrophosphate (TSPP), Na4P2O7, MW = 266, pH of 1% (w/w) solution in water = 9.80, solubility at 20 ◦C = 32 g/100 g H2O; and sodium hexametaphosphate (SHMP), (NaPO3)n, where n = 10 to 15, MW = (102)n, pH of 1% (w/w) solution in water = 6.6, solubility at 20 ◦C = 157 g/100 g H2O.

Fat emulsification and water stabilisation are the main requirements for a processed cheese matrix. These two features are achieved mainly by the presence of casein proteins when present in a natural cheese. It is a little more sophisticated because there are four types of casein present in natural cheese, one of which has been cleaved during cheese making. There are different casein hydrolysates present and the overall protein present in natural cheese is in the form of calcium paracaseinate.

The casein fractions form a three-dimensional network which are connected by calcium bridges.  However, these immobilised caseins cannot work as effective emulsifiers and stabilisers in the process cheese. Therefore, the basic role of any added emulsifying salts is to split off calcium ions from the cheese matrix and replace them with sodium ions. Complexation of calcium ions causes casein dissociation. 

By means of exchanging sodium ions for calcium ions, insoluble calcium paracaseinate changes into the more soluble and more hydrated sodium paracaseinate. This form can now function as a fat emulsifier and stabiliser in the processed cheese. The emulsification process is helped by the action of heating and shearing during manufacture. The outcome is then a process cheese with a more homeogeneous structure (Guinee et al., 2004).

The addition of phosphates, especially polyphosphates during manufacture produces firm and low melting cheeses (Templeton & Sommer, 1936; Gupta et al., 1984).

Shelf-Life Issues

Processed cheese is expected to be a much more stable product than natural cheese. However, most cheeses only have a shelf-life of a few months. Most foods change their flavour and structure over time. The warmer the temperature, the more dramatic the change. The topic is reviewed by 

 A series of changes occur to process cheese and natural cheese for that matter due to the following:-

• loss of water vapour,
• changes in ionic equilibria,
• crystal formation,
• lipid oxidation,
• hydrolysis of polyphosphates,
• nonenzymic browning,
• enzymatic activity
• interactions with packaging materials

The four main factors affecting the aging of a cheese are:-

• product composition,
• processing,
• packaging,
• storage conditions (time and temperature).   

Functional properties

The specific melting and rheological properties of process cheese i.e. cheese analog is a reflection of the behaviour of caseinate protein and added emulsifiers (Chen et al. 1979).

– Consistency, Firmness And Viscosity Of Processed Cheese

The consistency of processed cheese is affected by many factors (Bowland & Foegeding, 2001; Guinee et al., 2004). These include:-

• type and maturity of natural cheese,
• pH of cheese,
• fat content,
• type and concentration of emulsifying salt,
• processing conditions,
• dry matter content, presence and concentration of ions (especially
  calcium),
• use of hydrocolloids, etc. 

Firmness is the measure of the degree of product hardness. The term melting quality is used to denote the ease with which the cheese melts when subjected to heat (Weik et al., 1958).

For processed cheese, these are probably the two most important parameters in an assessment of overall quality. Cheese melting is dealt with elsewhere because of the complexity of the story. A PCF usually has a much softer texture and flavour than a processed cheese.

Amongst a number of factors, the degree of emulsification affects these two parameters to a great extent especially in processed cheeses (Templeton and Sommer, 1936; Rayan et al, 1980).

Manufacture

A processed cheese food is manufactured by blending shredded or minced natural cheese of varying quality and age with emulsifying salts and other ingredients. It is heated to around 85–90 °C.

Whether by design through the addition of acidulants and emulsifiers or just by a natural process of the mixed ingredients, the pH of a PCF is between 5.6 and 5.8.

The Key Physicochemical Changes in Making PCC

 When it comes to the manufacture of process cheese, we see a few key physicochemical events. the main step is the conversion of a natural cheese matrix into one which is shelf-stable. It requires emulsification of fat with a change in texture from relatively hard to soft and plastic in appearance. In fact one of the critical characteristics of the process is the ability to produce a variety of textures that are suited to slices or to spreads. 

In the process cheese manufacture, the cheese base changes texture where it becomes soft and malleable with melting even. This is the result of the application of both heat and shearing. As a result the casein become dispersed, the fat emulsifies with the soluble caseins. On cooling, a new texture is created because of the reforming of the basic casein structure into a new matrix.

The dispersion of the casein protein or peptization as it is called during cooking depends critically on the type and concentration of the emulsifying salts used.  These salts bind calcium and this mineral cation is required for cross-linking casein but also raising the pH. A change to a less acidic pH increases electrostatic repulsion.

Equipment Used in Processed Cheese Manufacture

The production of processed cheese involves several key pieces of equipment that allow for precise control over temperature, mixing, and emulsification:

1. Cheese Graters or Cheese Cutters: These are used to break down the natural cheese into smaller, more manageable pieces for further processing. This step ensures that the cheese blends evenly with other ingredients during the emulsification process.
2. Mixers and Blenders: Industrial mixers combine the base cheese with emulsifying salts, water, fats, and any other ingredients required by the formulation. Planetary mixers, Z-arm mixers, or horizontal mixers are commonly used, depending on the scale of production and the specific properties desired in the final product.
3. Cookers: The blended mixture is transferred to large cookers where it is heated to a specific temperature. Cookers can vary from simple kettles to more advanced steam-jacketed vessels with stirring mechanisms to ensure even heating. Continuous cooking systems, such as scraped surface heat exchangers, are often used for high-volume production to ensure efficient heating and mixing.
4. Emulsifying Equipment: Emulsifying salts are critical in processed cheese production as they break down protein structures and enable the cheese to melt more uniformly. Emulsification can be achieved through high-shear mixers, which create a fine dispersion of fat and water, resulting in a smooth, homogeneous product.
5. Homogenizers: Homogenizers may be used to create a fine, consistent texture in processed cheese by reducing the size of fat globules and ensuring an even distribution of ingredients. This is particularly important for cheese spreads or products with a very creamy texture.
6. Pasteurizers: Processed cheese is typically pasteurized to eliminate harmful microorganisms and extend shelf life. Pasteurization can be done through high-temperature short-time (HTST) methods, or in some cases, ultra-high temperature (UHT) processing is used.
7. Packaging Machines: Once the cheese is processed, it is either packaged hot or allowed to cool before packaging. For individual cheese slices, block molds, or loaf forms, automated packaging machines ensure that the cheese is wrapped and sealed in moisture-proof and air-tight packaging to prevent spoilage.

The Process of Making Processed Cheese

The manufacture of processed cheese involves several stages, each carefully controlled to produce a final product with consistent quality.

1. Selection and Preparation of Cheese

The process begins with the selection of base cheeses, which are often aged or matured to the desired flavor profile. These cheeses are shredded or grated to increase the surface area, allowing for more efficient mixing and emulsification. The cheese can either be a single type or a blend of different cheeses depending on the flavor and texture required in the final product.

2. Addition of Ingredients

Additional ingredients such as emulsifying salts (e.g., sodium phosphate, sodium citrate), water, cream, or milk powder are added to the cheese. Emulsifying salts play a critical role in processed cheese production by modifying the calcium-protein interaction in the cheese matrix. This adjustment prevents protein aggregation during heating, allowing the cheese to melt smoothly without becoming greasy or separating.

The ratio of these ingredients depends on the type of processed cheese being produced. For instance, processed cheese spreads have a higher moisture content than processed cheese slices or blocks, so more water or milk may be added during production.

3. Emulsification and Cooking

The cheese mixture is transferred to a cooker, where it is subjected to heat and mechanical agitation. The temperature typically ranges between 70°C to 90°C (158°F to 194°F), but this may vary based on the desired texture and properties of the final product. High temperatures are necessary to melt the cheese and activate the emulsifying salts, which stabilize the protein and fat emulsion.

In continuous production systems, the cheese mixture passes through a series of scraped surface heat exchangers or steam-heated kettles that provide both the heat and mechanical shear needed to achieve a smooth, uniform product. The heating step also serves as a pasteurization process, ensuring that the product is safe for consumption and has an extended shelf life.

4. Homogenization (if needed)

In some cases, particularly for processed cheese spreads or cheese with a very smooth texture, homogenization is used to break down fat globules and create a finer, more consistent texture. This step ensures that the final product has an even mouthfeel and is free from lumps or graininess.

5. Cooling and Setting

Once the desired texture is achieved, the cheese is either cooled immediately or formed into blocks or slices while still hot. If the cheese is to be formed into slices or loaves, it is poured into molds and allowed to cool and solidify. For processed cheese spreads, the product is typically cooled before being packed into tubs or jars.

Process Conditions

Several key process conditions are crucial in processed cheese manufacture:

• Temperature: Controlling temperature is essential to ensure that the proteins denature correctly and the emulsifying salts function as intended. Too high a temperature can cause protein degradation, while too low a temperature may prevent adequate emulsification.
• pH: The pH of the cheese mixture is carefully controlled during processing to optimize the function of emulsifying salts and to stabilize the cheese proteins. Processed cheese typically has a pH range of 5.4 to 5.6, but this can vary based on the desired texture and melting properties.
• Moisture Content: Processed cheese typically has a higher moisture content than natural cheese, which contributes to its smooth, creamy texture and meltability. The moisture content is controlled by the amount of water or milk added during the mixing stage.

Variations in Processed Cheese Manufacture

There are several variations in the production process depending on the type of processed cheese being manufactured:

1. Processed Cheese Slices: For individually wrapped slices, the cheese mixture is poured onto cooling belts or rollers and formed into thin sheets. The sheets are cut into slices and packaged individually.
2. Processed Cheese Blocks: For block or loaf cheese, the hot cheese mixture is poured into molds, where it cools and solidifies. These blocks are then vacuum-sealed to maintain freshness and prevent moisture loss.
3. Processed Cheese Spreads: These products have a higher moisture content and are often made with additional cream or milk. The cheese mixture is emulsified and cooled before being packed into jars or tubs. Some processed cheese spreads may be aerated during production to give them a lighter, fluffier texture.
4. Processed Cheese with Additives: In some cases, additional ingredients such as flavorings (e.g., jalapeños, herbs), colorants, or preservatives are added to enhance the flavor, appearance, and shelf life of the processed cheese.
5. Low-Fat or Fat-Free Processed Cheese: For low-fat versions, manufacturers may replace some of the fat with fat replacers like whey protein or other hydrocolloids. These products require careful formulation and processing to ensure they still have the desired texture and melting properties despite the reduced fat content.

Fouling Issues In The Manufacture Of Processed Cheese

Fouling is a significant issue during the production of processed cheese, especially given the complex mixture of proteins, fats, salts, and other components involved. Processed cheese production often involves heat treatment, mixing of emulsifiers, and blending of various dairy ingredients, which can all contribute to the deposition of materials on equipment surfaces. These deposits, or fouling layers, can affect the efficiency of heat exchangers, homogenizers, and other critical equipment, leading to reduced performance and sanitation challenges.

Main Fouling Materials in Processed Cheese Production

The primary fouling materials during processed cheese production are a combination of organic and inorganic compounds:

1. Proteins (Casein and Whey Proteins): Proteins from milk, particularly casein, play a central role in processed cheese formation. Casein is often used in large quantities during cheese production. At high temperatures, proteins can denature, leading to aggregation and deposition on surfaces. This fouling can be exacerbated in the presence of emulsifying salts that adjust the protein structure, causing proteins to interact more strongly with surfaces.
2. Fats: Milk fats are another key component in cheese production. These fats can melt during the heating processes and adhere to surfaces of equipment such as heat exchangers or pasteurizers. The interaction between fat globules and proteins can form a persistent fouling layer that is difficult to remove without proper cleaning agents.
3. Emulsifying Salts: Salts like sodium phosphate, sodium citrate, and sodium chloride are used to adjust the pH and promote protein emulsification in processed cheese. These salts can react with proteins and fats to form complexes that further contribute to fouling. The presence of these salts can also affect the solubility of proteins, making fouling more pronounced.
4. Calcium Phosphate: Calcium phosphate is indeed a significant fouling issue in dairy systems, including during processed cheese production. It forms when calcium from milk interacts with phosphate ions, leading to the precipitation of calcium phosphate on surfaces. This mineral scale can build up, especially in heat-exchange equipment where high temperatures and concentrations of calcium and phosphate lead to crystallization. The fouling caused by calcium phosphate is typically tough and can severely impede heat transfer efficiency, making it a critical issue in cheese production​ (Nature).
5. Lactose: Although lactose is present in lower concentrations in processed cheese compared to other dairy products, it can still contribute to fouling. During heat treatment, lactose can undergo Maillard reactions with proteins, forming a sticky, brown deposit on surfaces that is particularly challenging to clean.

Fouling Mechanisms in Processed Cheese Production

Fouling occurs through several mechanisms, depending on the components involved and the equipment used in the process:

1. Protein Denaturation and Aggregation: Proteins such as casein and whey proteins tend to denature when exposed to heat. Denatured proteins lose their native structure and become prone to aggregation. These aggregated proteins can adhere to equipment surfaces, forming a fouling layer that grows over time.
2. Fat Melting and Deposition: As the temperature rises during cheese processing, fats in the cheese melt and can coalesce. These fats are hydrophobic and tend to adhere to the surfaces of equipment. The interaction between melted fats and denatured proteins can form a more complex and persistent fouling layer.
3. Mineral Precipitation: Calcium phosphate fouling is a common issue, particularly in heat exchangers. When milk is heated, calcium and phosphate ions present in the milk can become supersaturated, leading to the precipitation of calcium phosphate. This mineral fouling typically forms a hard, crystalline layer on the surfaces, which reduces heat transfer efficiency.
4. Lactose Crystallization: Lactose can crystallize under certain conditions, particularly in processes that involve evaporation or concentration. Crystallized lactose can adhere to surfaces and contribute to fouling, although this is less of an issue in processed cheese compared to other dairy products like condensed milk.
5. Interaction Between Components: Processed cheese contains a complex mixture of proteins, fats, and salts. These components can interact in ways that enhance fouling. For example, emulsifying salts can destabilize proteins, increasing their propensity to foul surfaces. Similarly, interactions between proteins and fats can form composite fouling layers that are more difficult to remove than individual components.

The Role of Calcium Phosphate in Fouling

Calcium phosphate is a well-known contributor to fouling in dairy processing, and it plays a significant role in processed cheese production. Calcium is naturally present in milk, and when combined with phosphate ions (which are often added as part of emulsifying salts), it can form calcium phosphate deposits. These deposits typically form at elevated temperatures, especially in heat exchangers where heating and cooling cycles lead to the supersaturation of calcium and phosphate ions.

In processed cheese production, emulsifying salts like sodium phosphate are added to adjust the texture and consistency of the cheese. These salts interact with the calcium present in milk proteins, promoting the emulsification of fats and proteins. However, the presence of phosphate ions also increases the likelihood of calcium phosphate precipitation.

The precipitation of calcium phosphate is influenced by several factors:

• Temperature: High temperatures promote the supersaturation of calcium and phosphate ions, leading to precipitation. This is particularly problematic in equipment that involves heating, such as pasteurizers and heat exchangers.
• pH: The solubility of calcium phosphate is pH-dependent. Processed cheese production often involves pH adjustments to optimize protein functionality, but these changes can also promote calcium phosphate precipitation.
• Concentration of Calcium and Phosphate Ions: High concentrations of calcium and phosphate in the milk or cheese matrix can increase the likelihood of calcium phosphate fouling.

Effects of Fouling in Processed Cheese Production

Fouling can have several detrimental effects on processed cheese production:

1. Reduced Heat Transfer Efficiency: Fouling, particularly from calcium phosphate and protein deposits, can reduce the efficiency of heat exchangers by forming an insulating layer on heat transfer surfaces. This can lead to longer processing times, increased energy consumption, and inconsistent product quality.
2. Increased Cleaning Frequency: Fouling requires more frequent cleaning to maintain equipment performance. In severe cases, production must be halted for cleaning, leading to downtime and reduced throughput.
3. Sanitation and Microbial Risks: Fouling can create niches where microorganisms can thrive, particularly if biofilms form on top of fouling layers. This can pose a risk to product safety and require additional cleaning and sanitization efforts.
4. Product Contamination: If fouling layers detach during processing, they can contaminate the final product with particles of denatured protein, fat, or calcium phosphate. This can affect the texture, flavor, and quality of the cheese.

Cleaning and Mitigation of Fouling

Effective cleaning procedures are essential to remove fouling deposits and maintain the efficiency of equipment in processed cheese production. Common cleaning strategies include:

1. Cleaning-in-Place (CIP) Systems: CIP systems are widely used in dairy processing to remove fouling without disassembling equipment. CIP systems typically involve:
   • Pre-rinsing with water to remove loose deposits.
   • Alkaline cleaning to remove protein and fat fouling. Alkaline detergents (e.g., sodium hydroxide) are effective at breaking down organic deposits.
   • Acid cleaning to remove mineral deposits, particularly calcium phosphate. Acidic solutions (e.g., phosphoric acid) help dissolve calcium phosphate and other mineral scales.
   • Final rinsing to remove cleaning agents and ensure the system is ready for use.
2. Enzymatic Cleaners: Enzymatic cleaners contain specific enzymes that target proteins, fats, or carbohydrates. These cleaners can be used to break down complex fouling layers that are difficult to remove with traditional alkaline or acid cleaners.
3. Mechanical Cleaning: In some cases, particularly for severe fouling, mechanical cleaning (e.g., scrubbing or scraping) may be necessary to remove deposits. However, this is typically used in combination with chemical cleaning for maximum effectiveness.
4. Optimizing Processing Conditions: Adjusting temperature, pH, and flow rates can help reduce the rate of fouling. For example, operating at lower temperatures can reduce protein denaturation and fat melting, while controlling pH can minimize calcium phosphate precipitation.

Fouling in processed cheese production is a complex issue that involves the accumulation of proteins, fats, calcium phosphate, and other materials on equipment surfaces. Calcium phosphate fouling is particularly problematic in high-temperature processes and can significantly reduce the efficiency of heat exchangers. Understanding the mechanisms of fouling and implementing effective cleaning procedures, such as CIP systems and enzymatic cleaners, is crucial for maintaining equipment performance and ensuring product quality. By optimizing processing conditions and cleaning strategies, dairy producers can minimize fouling and enhance the efficiency of processed cheese production.

References

Abd‐El‐Salam, M.H., Al‐Khamy, A.F., El‐Garawany, G.A., Hamed, A., Khader, A. (1996) Composition and rheological properties of processed cheese spread as effected by the level of added whey protein concentrates and emulsifying salt. Egypt J. Dairy Sci. 24 pp. 309–22

Barker, C. R. (1947). Practical suggestions on the manufacture of process cheese. Nat. Butter Cheese J. 38: pp. 42,44,46

Berger, W., Klostermeyer, H., Merkenich, K., Uhlmann, G. (1989) Processed cheese manufacture: a JOHA guide. Ladenburg, Germany : BK Ladenburg. 238 p.

Bowland, E. L., & Foegeding, E. A. (2001). Small strain oscillatory shear and microstructural analyses of a model processed cheese. Journal of Dairy Science, 84, pp. 2372-2380

Caric, M., Gantar, M., & Kalab, M. (1985). Effects of emulsifying agents on the microstructure and other characteristics of process cheese-a review. Food Structure, 4(2), pp. 13

Davel, H. B., & Retief, D. J. (1928). Manufacture of Loaf Cheese. New York Produce Review and American Creamery, 65, pp. 384.

FDA. (2006). 21 CFR, Part 133.169 to 133.180. United States Food and Drug Administration. Department of Health and Human Services, Washington, DC.

Fox, P.F., Guinee, T.P., Cogan, T.M., McSweeney P.L.H. (2000) Processed cheese and substitute or imitation cheese products. In: Fundamentals of cheese science. Gaithersburg, Md.: Aspen Publishers Inc. p 429–41  .

Georgakis, S.A. (1975) Concentration of whey protein by ultrafiltration and its use for processed cheese manufacture. In : Proc. 20th World Vet Congr. 1, pp. 835-838

Guinee, T. P., Carič, M., & Kaláb, M. (2004). Pasteurized processed cheese and substitute/imitation cheese products. In: P. F. Fox, P. L. H. McSweeney, & T. P. Cogan (Eds.), Cheese: Chemistry, physics and microbiology. Major cheese groups, Vol. 2 (pp. 349—394). London, New York: Elsevier Applied Science (Article).

Gupta, V.K., Reuter, H. (1992) Processed cheese foods with added whey protein concentrates. Lait 72, pp. 201-212

Gupta, S.K., Karahadian, C., Lindsay, R.C. (1984) Effect of emulsifier salts on textural and flavour properties of processed cheese. J Dairy Sci. 67, pp. 764-778 (Article)

Kapoor, R., & Metzger, L. E. (2008). Process cheese: scientific and technological aspects — a review. Comprehensive Reviews in Food Science and Food Safety, 7, pp. 194-214 (Article).

Kapoor, R., Metzger, L. E., Biswas, A. C., & Muthukummarappan, K. (2007). Effect of natural cheese characteristics on process cheese properties. Journal of Dairy Science, 90(4), pp. 1625-1634 (Article)

Lee SK, Klostermeyer H. (2001). The effect of pH on the rheological properties of reduced-fat model processed cheese spreads. Lebensm Wiss U Technol 34 pp. 288–292.

Marchesseau, S., Gastaldi, E., Lagaude, A., Cuq, J.L.(1997) Influence of pH on protein interactions and microstructure of process cheese. J. Dairy Sci. 80 pp. 1483–9 (Article).

Mizuno, R. & Lucey, J.A. (2005a). Effects of emulsifying salts on the turbidity and calcium-phosphate-protein interaction in casein micelles. Journal of Dairy Science, 88, pp. 3070–3078 (Article).

Mizuno, R. & Lucey, J.A. (2005b). Effects of two types of emulsifying agents on the functionality of nonfat pasta filata cheese. Journal of Dairy Science, 88, pp. 3411–3425.

Mizuno, R. & Lucey, J.A. (2007). Properties of milk protein gel formed by phosphates. Journal of Dairy Science, 90, pp. 4524–4531.

Price, W.V. (1929) A Color Defect of Process Cheese. Journal of Dairy Science, 19 pp. 377. 

Rayan, A. H. (1981). Microstructure and rheology of process cheese. Ph.D thesis. Utah State University.

Sádlíková, I., Buňka, F., Budinský, P., Barbora, V., Pavlínek, V., & Hoza, I. (2010). The effect of selected phosphate emulsifying salts on viscoelastic properties of processed cheese. LWT-Food Science and Technology, 43(8), pp. 1220-1225   

Schär, W., & Bosset, J. O. (2002). Chemical and physico-chemical changes in processed cheese and ready-made fondue during storage. A review. LWT-Food Science and Technology, 35(1), pp. 15-20 (Article)

Shirashoji, N., Jaeggi, J. J., & Lucey, J. A. (2006). Effect of trisodium citrate concentration and cooking time on the physicochemical properties of pasteurized process cheese. Journal of Dairy Science, 89(1), pp. 15-28 (Article).

Stampanoni, C.R., Noble, A.C. (1991). The influence of fat and salt on the perception of selected taste and texture attributes of cheese analogs. A scalar study. J Text Stud. 22 pp. 367–80   .

Templeton, H. L., & Sommer, H. H. (1936). Studies on the emulsifying salts used in processed cheese. Journal of Dairy Science, 19(8), pp. 561-572.

Weik, R.W., Combs, W.B., Morris, H.A. (1958) Relationship between melting quality and hardness of Cheddar cheese. J Dairy Sci. 41, pp. 375-
381