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.
Process 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: 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).
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.
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.
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