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Answers to selected cheese technology questions

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Q: Concentration of fat in Cheddar-cheese whey
What is the concentration of fat in un-separated Cheddar-cheese whey?

A: 0.3% (w/w).

Q: Standardisation
Why is milk for cheese manufacture standardised?

A: 1. To ensure the manufacture of a consistently high quality product by maintaining casein:fat ratio at the optimal value for the variety being produced; e.g. a value of 0.7 : 1 and a fat to SNF ratio of 2.8 : 1, are used in Cheddar manufacture. The casein/fat ratio directly influences the fat in dry matter, body and texture all of which markedly affect product quality.

2. For legal reasons to ensure that the minimum FDM content is consistently achieved.

Q: Cheese yield definition
Define the term cheese yield.

A: Practical cheesemakers define yield as the weight of cheese obtained from a given volume or weight of milk e.g equation 1.

Equation 1: cheese yield = weight of cheese (kg) x100 /weight of milk (kg). Note that the results are expressed as a percentage e.g. 10% yield. Note that this approach does not include all the inputs e.g. salt and starter. Hence a more valid approach would be to include all the inputs as in equation 2.

Equation 2 cheese yield = weight of cheese (kg) x 100/
weight of milk (kg)+weight of starter(kg)+ weight of salt(kg).

Q: Yield potential
What does yield potential mean?

A: This can be expressed as the maximum amount of cheese of satisfactory composition that can be obtained from a given quantity of milk. This is directly dependant on the concentration of casein and fat in the milk.

Q: Van Slyke equation
State the Van Slyke equation and explain the significance of the terms used.

A: The Van Slyke equation states that the predicted yield of Cheddar cheese, Y,:

Y = (0.93 x % M.fat) + (% M. casein-0.1) x 109
---------------------------------------------------------
100-moisture in cheese

where

% M. fat = % fat in milk and
% M. casein = % casein in milk.

Yield is expressed as kg of cheese/100 kg of milk or as a %.
The 0.93 x milk fat assumes that some 93% of milk fat is retained in the cheese.

The value for casein - 0.1 approximates to a theoretical loss of 4% casein and a casein retention of approximately 96%. e.g consider milk containing 2.5% casein, then the loss in casein = 2.5-0.1/2.5x100 = 96% . This loss is equivalent to the glycomacropeptide produced by the hydrolysis of kappa casein by chymosin.

The 109 is a constant to allow for milk salts, retention of whey protein and lactose.

The equation can be rewritten by removing moisture and replacing it with a specific moisture value e.g. 35% and the 0.1 with the concentration of casein lost in the whey in the form of glycomacropeptide (4%) to give a value of 0.96C for milk casein. The equation can then be simplified and expressed using casein and fat only. This can be used to predict the yield of Cheddar cheese having a target moisture value.

Providing the milk is standardised to a target casein: fat ratio, and this is maintained through the year, this equation can give surprisingly good results.

Q: Cheese yield calculation.
Milk of 2.5% casein and 3.8% fat was used to produce Cheddar cheese of 36% moisture. Calculate the theoretical yield of cheese expected from 1000 kg of this milk.

A: Using the Van Slyke yield equation

Theoretical yield = (0.93 x 3.8 (fat in milk)) + (2.5 (casein in milk) - 0.1) x 109
----------------------------------------------------------------
100 -36(moisture in cheese)

= (3.534) + (2.4) x 109
-------------------------------
64

= 10.1 %

101 kg cheese from 1000 kg milk

Q: Actual yield is lower than the theoretical yield. If the actual yield of cheese was 10% lower than the theoretical yield what would be the significance of this finding?
A: Firstly the possibility of errors in analysis of milk components and cheese moisture should be considered.

Very small errors in the determination of milk components will result in large errors in predicted yield. Yield equations work best with standardised milk and where the ratio of casein to fat is maintained at a target value.

The reduced yield should therefore be confirmed before embarking on a project to increase yields. If results are validated then these results indicate potential for economic loss.

The yield reduction may be due to poor cheese making technique resulting in low casein and/or fat retention. Casein and fat retention should therefore be determined. See determination of process efficiency below.

The possibility of high losses of fines should also be considered. Fine concentration in the whey should be determined.

Milk of poor bacteriological quality and containing microbial-proteases may have been used. See section on cheese yield at https://www.dairyscience.info/index.php/cheese-yield.html also.

The milk may have been stored for several days prior to use.

Q: Process efficiency
How can you determine process efficiency in cheese manufacture?

A: There are several approaches to determining process efficiency. One approach is to compare actual yield with theoretical yield as determined using a yield equation. The difference in yields can be expressed as a percentage and the closer this value is to 100% then the higher the value for process efficiency. This is shown below.

Process efficiency =

Actual yield x 100
------------------------------
Theoretical yield

Alternatively casein, fat and protein retentions can be calculated and compared with benchmark values, if the actual retentions are significantly lower this indicates that process efficiency is low. Again these differences can be expressed as percentages.

The equations for comparing fat, casein and protein retentions with theoretical values are given below:

i. % retention of fat = kg cheese x % fat (cheese) x 100
kg milk x % fat (milk)

ii. % retention of protein = kg cheese x % protein (cheese) x 100
kg milk x % protein (milk)

iii. % retention of casein = kg cheese x % casein (cheese) x 100
kg milk x % casein (milk)

Q: Retention of protein, fat and casein in Cheddar cheese.
List the retention values for: protein, fat and casein in Cheddar cheese.

A: Typical retention values for protein, fat and casein in Cheddar cheese:

Protein- 76%

Fat- 92%, higher values are possible

Casein- 91%, higher values are possible.

Q: Mechanisation
Explain the advantages of cheese mechanisation.

A: Cheese mechanisation was primarily introduced to reduce labour costs by reducing staffing levels. Mechanisation has also the potential to obtain a higher level of product consistency and potentially improved quality compared with manual production systems. Because of the reduced level of handling the potential for contamination is also reduced

Q: Definition of Mellowing
What do you understand by Mellowing?

A: This term is used to describe a stage during the manufacture of dry-salted cheeses such as Cheddar and Cheshire in which salt is added to the milled curd. This is where salt adsorption takes place prior to pressing. This is a critical, sometimes neglected stage that has the potential to influence yield and salt and moisture distribution in the cheese. See response below.

Q: Cheese
What is cheese?

A: Because of the diversity of cheeses and the continual developments in technology, e.g. the use of ultrafiltration, it can be difficult to use just a single definition to define cheese.

The Food and Agriculture Organisation of the United Nations (FAO) has defined cheese as the fresh or matured product obtained by the drainage (of liquid) after the coagulation of milk, cream, skimmed or partly skimmed milk, buttermilk or a combination thereof.

Since this does not apply to whey cheeses such as Ricotta, the FAO included a second definition for whey cheeses: Whey cheese is the product obtained by concentration or coagulation of whey with or without the addition of milk or milk fat.

Q: Casein
Casein constitutes ?% of milk protein?

A: Casein accounts for some 80% of milk protein.

Q: How do you convert grams of sodium to % salt?
How do you convert grams of sodium to % salt?

A: The simple answer is to multiply the concentration of sodium in 100 grams of the food by 2.5. This will give the approximate % salt concentration.

The factor 2.5 is an approximation. The actual factor can be calculated using the formula weights of sodium and sodium chloride. Sodium has a formula weight of 22.98977 atomic mass units, sodium chloride has a formula weight of 58.4428 atomic mass units. The ratio of sodium chloride to sodium is 58.4428/22.98977 which =2.542, approximately 2.5. Hence the use of 2.5 to multiply grams of sodium to obtain % salt.

The figure, 2.5, can also be derived by calculating the % of sodium in salt and dividing the formula weight of sodium chloride by the % of sodium in the compound. The % sodium in salt = 22.98977 / 58.4428 x 100 =39.34%. Dividing the formula weight of sodium chloride by the % of sodium in the compound gives the sodium to salt conversion factor, 58.4428/39.34, namely 2.542 or 2.5 approximately.

There is a sodium to salt calculator at https://www.dairyscience.info/sodium/salt.asp.

Q: Whey components
What is the concentration of fat in separated Cheddar-cheese whey

A: 0.03 % fat (w/w).

Q: Retention values
List target retention values for protein, fat and casein in Cheddar cheese.

A: Typical retention values (benchmarks) for protein, fat and casein in Cheddar are 76%, 91% and 93% respectively. See the Ebook for more detailed information.

Q: Rennet mixing time.
Explain the importance of rennet mixing time.

A: Correct mixing of rennet with milk is essential. The mixing time must be sufficiently long to ensure that the rennet has been distributed homogeneously. However, if the mixing time is excessive then the new forming coagulum will be disrupted with excessive fat losses.

Because the volume of rennet used is small compared with the volume of milk, it is customary to dilute the rennet with water and to add the diluted coagulant to the milk.

The consequence of inadequate stirring is an uneven distribution of the coagulant. This may lead to localised action of the coagulant on the casein micelles, resulting in a firmer coagulum in areas correlating to higher coagulant concentrations and vice versa. The weaker coagulum may be damaged with loss of fat and yield.

Q: Moisture level in Cheshire cheese is too high
What can the cheesemaker do to bring the moisture level down?

A: In this situation the rate of syneresis was too low. The solution is to increase the rate.

Firstly it is recommended that the casein: fat ratio should be determined and if incorrect the the milk should be standardised to the correct CF ratio e.g. the fat content of the milk might be too high.

Other actions that might be taken include:

-increasing the rate of acid production by the starter
- rennetting the milk at higher acidity
- increasing the maximum scald temperature e.g. try using 2°C increments
-holding the curds at maximum scald temperature for a longer period- e.g. try using 3 minute increments
- cutting the coagulum smaller
- stirring the curd in the whey for longer
- pitching at higher acidity
- keeping the curd warm during ‘cheddaring’
-checking the temperature of the cheese room and increasing the temperature if necessary.

Q: The moisture level in Cheddar cheese is too low.
What can the cheesemaker do to increase moisture levels?

A: In this scenario the low moisture in Cheddar suggests that the rate of
syneresis was excessive. The solution is to decrease the rate.

Firstly it is recommended that the casein: fat ratio should be determined and if incorrect the the milk should be standardised to the correct CF ratio e.g. the fat content of the milk might be too low.

Other actions that might be taken include:

1. Reducing the maximum scald temperature
2. Reducing the stirring rate
3. Increasing the curd particle size i.e cut the curd into larger cubes
4. Lowering the starter inoculum level and decreasing the length of the make process- using a lower starter inoculum will reduce the rate of acid production and slow down syneresis.

Q: Starter failure in cheese manufacture
List the main causes of starter failure in cheese manufacture.

A: The major causes of slow acid production by cheese starters in the United Kingdom were reported in 1981 by the author and colleagues, table 2. These results suggested that phage and antibiotics were responsible for the majority of problems.

Table 2. Main causes of slow starter activity

-----------------------------------------------------------% of Factories
i. Bacteriophage only---------------------- 34
ii. Antibiotics only--------------------------------- 24
iii. Poor bacteriological quality of milk ---------- ------------ 3.5
iv. Bacteriophage and antibiotics ---------------- ------------ 3.5
v. Bacteriophage, and detergent and sterilant residues------------------- 3.5
vi. Antibiotics, detergent and sterilant residues ------------------------------ 3.5
vii. Coliform and agglutination*-------------------------- 3.5
viii. Starter cultures----------------------------------------------------- 7
ix. Operational errors ---------------------------- ------------------------------ 10.5
Source: Walker et. al.(1981 )

Other factors including sterilant and detergent residues, poor quality milk, and excessive scald temperatures can also cause problems. Additionally consideration should also be given to ‘sabotage’ by disaffected persons.

Q: Factors influencing syneresis
List the major factors influencing syneresis in cheese manufacture.

A: Traditional cheesemaking is essentially a process for removing moisture from a rennet gel. This moisture removal process is termed syneresis.

The major factors that promote syneresis include:

increased acid production by starter
increasing the temperature of scalding
increasing the length of the 'scalding' period
increasing rennet concentration
decreasing curd particle size
increasing stirring rate

Synerysis is reduced:

as the fat concentration in milk increases
as the protein level in milk increases
if the milk is homogenised
if the milk has been stored for extended periods at low temperatures
if milk containing high levels of psychrotrophic bacteria is used
if high pasteurisation temperatures are used.

Q: Ingredients used in Cheddar and Feta manufacture
List the ingredients used in the manufacture of Cheddar and Feta cheeses.

A: Ingredients used in traditional Cheddar and Feta manufacture

CHEDDAR CHEESE ------------------------ FETA CHEESE

Cows’ milk -------------------------- Goats’ milk, ewe’s milk, mixture of goat and ewe milk. Note! Cows' milk with colour removed and / or mixed with goat and/or ewe milk may also be used.
Starter culture---------------------- Starter culture
Salt --------------------------------- Salt
Calcium chloride-------------------- Calcium chloride
Annato ---------------------- ------- Lipase preparation (if cows' milk used)
Rennet -------------------------- --- Rennet
----------------------- ------------- - Decolouriser (if cows' milk used)

Q: Modelling cheese quality

Q: Discuss the model proposed by Lawrence and colleagues for assessing Cheddar cheese quality.

A: During maturation, bacteria and enzymes act on the fat, protein and carbohydrate in the cheese to produce the body, texture and flavour characteristic of mature Cheddar and other cheeses. The changes in body and texture that transform the rubbery, elastic mass of curd to a cheese with a firm close texture are the results of protein and fat degradation. The release of volatile components from the curd gives the aroma to cheese and associated flavours.

Assessment of cheese quality is essential in order to determine if the cheese conforms to legal standards, meets the requirements of the buyer and ultimately the customer and to grade the cheese for payment. A cheese may meet all legal and safety requirements but have appearance, flavour and or texture defects that make it unsuitable for consumer use. The traditional method of assessing cheese quality is by organoleptic assessment by a cheese grader. Until relatively recently the suitability of cheese for end consumer use was judged almost entirely on flavour and texture assessments by commercial cheese graders. To assess the cheese, the cheese grader visually examines the outside, and an inner core of the cheese. Examination of the sample core, immediately on withdrawal from the cheese, provides the grader with indices of aroma, colour, texture and body. These typically form the basis of traditional approaches to cheese grading.

Increasingly, chemical and physiochemical indicators are being used in conjunction with more traditional cheese grading particularly when selecting cheese for extended maturation.

One approach to the use of cheese quality modelling and the development of a research-based approach to the selection of cheese for extended maturation has been developed in New Zealand.

Extensive research in New Zealand by Bob Lawrence and his colleagues found that many Cheddar cheeses selected for export, by grading at 14 days, had considerably deteriorated when graded later at five months. In efforts to focus the New Zealand dairy industry on a more uniform end product that would facilitate the development of new markets a model for predicting Cheddar cheese quality was developed by Lawrence and his colleagues. This model was an attempt to grade Cheddar cheese into grade categories based on an analysis of chemical and physiochemical components, 24 hours after cheese manufacture.

The model was based on four main compositional factors.

1. The percentage of salt in moisture (S/M): S/M is the major factor controlling water activity (Aw) in young Cheddar cheese. Aw will influence the rate of bacterial and enzyme activity e.g. the activity of residual chymosin within the curd and can be used to influence the microflora of the mature cheese. Cheese makers should aim for a S/M percentage which when combined with temperature control will allow the metabolism of lactose by the starter bacteria at a controlled rate and reduce the potential for growth of non-starter lactic acid bacteria such as lactobacilli. At S/M percentages of <3.5% there is greater potential for starter growth to high cell densities with the risk of bitter flavour development and more rapid growth of non-starter lactic acid bacteria with further potential flavour and body defects. Proteolysis by residual coagulant will also be greater, increasing the potential of off flavour and body defects.

At S/M levels of > 6%, lactose metabolism by starter cultures is effectively inhibited, resulting in at best, slow ripening cheese with flavour and texture defects.

On the other hand at S/M concentrations > 4% and <6 % Lawrence and others have found that there is a high probability of cheese of at least satisfactory quality being produced.

2. Moisture in, the fat-free-substance (MFFS): This is an indication of the relative amounts of moisture and casein in the cheese. The effect of moisture is more closely related to the amount of moisture per unit of casein since it is in the matrix (3) of moisture and casein that the enzymatic reactions responsible for ripening largely take place. Several workers have found that MFFS was a major compositional parameter affecting grade of cheese and cheese quality in general. There is now convincing evidence that it is the relative hydration of the casein in the curd, rather than the overall moisture content that influences the ripening process

3. Fat in the dry matter or fat in the water-free substance (FDM or FWFS): While FDM has the potential to have a significant effect on the body of Cheddar cheese this parameter is relatively easily controlled by standardisation of the casein to fat ratio in the raw milk. As it is the casein matrix that binds the fat, the more fat present the weaker the body and vice versa. It should be noted however that relatively large ranges of FDM, within the legal range for Cheddar, can be tolerated.

4. pH: The pH of cheese curd is one of the distinguishing characteristics that can differentiate cheese types. The pH and the ratio calcium/ Kg of solids-not-fat (SNF) can be used to classify traditionally manufactured cheese varieties. pH like S/M also influences rates of enzymatic and bacterial activity. Manipulation of pH can be used to influence the microflora of the mature cheese. The pH of the curd at one day post manufacture gives an indication as to the extent of acid development during manufacture and the level of preservation and the potential 'safety' of the cheese. The potential for further acid development is dependent on the residual lactose in the curd and the buffering capacity of the curd.

The model developed by Lawrence et al uses the four compositional factors outlined previously and through analysis of an extensive volume of results obtained from commercial cheese plants sets limits on each. The limits are divided into two categories, that of Premium and First grade cheese (figue available in E-book). Lawrence suggests that if a curd falls within the specifications for Premium and has no flavour defects at 14 days it is suitable for export and hence long maturation.

Limitations of the Lawrence model

Many models have limitations and it is therefore not surprising that the Lawrence model also has some limitations. Refer to https://www.dairyscience.info/index.php/cheese-quality/66-modeling-the-grade-value-of-cheddar-cheese.html.

Q: Acidity at whey drainage and cheese structure
Using an appropriate model explain the differences between Emmental, Cheddar, Cheshire and Gouda cheese.

A: Acidity and calcium model of Lawrence and colleagues

There are many ways in which traditional cheeses can be classified. For example country of origin, type of milk used, species of animal used to produce the milk, fat content, moisture content, texture, whether mould ripened or not, cheese making process used, moisture in the non-fat solids and many more criteria have been used either singly or in combination.

These descriptive approaches, while helpful in some respects, were limited in that they provided no theoretical insight into why one cheese was different from another.

Lawrence et. al. (1984) suggested that cheeses should be classified on the basis of two criteria, pH and their calcium content. This approach is summarised below. See the article on this site at https://www.dairyscience.info/index.php/cheese-manufacture/114-classification-of-cheese-types-using-calcium-and-ph.html.

Swiss, Gouda and Cheshire cheeses exhibit a narrow range for pH and calcium content compared with Cheddar. Cheddar has a much wider range for both pH and calcium content. Lawrence et. al. (1984) suggested that Cheddar is a popular variety because this cheese type can have a wide range for pH and calcium content yet can still meet customer expectations.

The model proposed by Lawrence and his colleagues suggests that the differences between the various traditional cheese types are based to a large extent on the basic structure of the cheese. This basic structure is ultimately determined by the properties of the protein matrix in the cheese which is dependent on the pH of the whey at the point when the curds and whey are separated; this point may be called whey-run off, drainage, whey removal. It is at this point where the mineral content of the cheese and its residual lactose content are largely determined. The residual lactose will influence the lowest pH, highest level of acidity, that can be attained.

Why does pH at whey run off or drainage determine cheese type? The explanation involves the effect of pH on the casein micelle and ultimately on the protein aggregates in cheese.

The casein micelle is composed of numerous sub-micelles, which are held together by colloidal calcium phosphate. As pH decreases, acidity increases, the calcium phosphate becomes soluble and the casein micelle starts to disassemble. This process can be monitored by measuring the size of protein aggregates using electron microscopy.

The mineral content of cheese is largely determined by the quantity of calcium phosphate lost from the curd, which is mainly dependant upon the pH of the whey at drainage; pH is dependant on starter activity. It is this loss of calcium phosphate, and its effect on the properties of the protein aggregates in cheese, that is critical to the development of cheese type.

Low acid cheeses such as Swiss have a high mineral content and have protein aggregates largely composed of intact casein micelles. Electron microscopy reveals an extensive protein matrix composed of strings of protein aggregates. Such cheeses
have relatively elastic properties.

At the other extreme Cheshire cheese has a low mineral content and has very small protein aggregates. This cheese has virtually no elasticity; it is ‘crumbly' and will break easily. Electron microscopy reveals a very weak internal protein matrix.
Cheddar is intermediate between Gouda and Cheddar with regard to the size of protein aggregates and the density and strength of the internal protein matrix.
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Q: Starter functions
Explain the role of starters in cheese manufacture.

A: Starter cultures have a major role in cheese manufactue. Initially they produce the lactic acid that aids rennet action and promotes moisture removal from the coagulam, synerysis. The starter also produces flavour compounds and helps preserve the cheese. The main effects of starter are are discussed in more detail in the Ebook and the dairyscience.info website. The lowering of redox potential is critical to providing the correct environment for flavour generation in varieties like Cheddar. Utilisation of residual lactose is also a major starter function. Starters also have an important role in cheese maturation.

Q: Bitterness in cheese
What causes bitterness in cheese?

A: There are several reasons why bitterness may develop in cheese. With a few exceptions bitterness is generally associated with proteolysis.

Protein breakdown is critical to texture and flavour development in many cheeses. However, the process can generate hydrophobic peptides that if present at a sufficiently high concentrations can give rise to bitterness. Because these peptides are soluble in fat bitterness tends to be more of a problem in reduced fat varieties.

There has been considerable research into the causes of bitterness in Cheddar and Gouda cheeses and there is now a good understanding of 1) the mechanisms responsible for bitterness and 2) how to prevent or control bitterness.

The following is an attempt at summarising and simplifying how bitterness is produced. The coagulant, rennet, hydrolyses casein to produce polypeptides. These are then degraded to peptides and amino acids by peptidases associated with the membrane proteins of the starter cultures, lactococci, used in the cheese making process.

Bitterness will only develop if a number of conditions are met namely, the cheese must be of relatively low salt in moisture (S/M) content, bitterness is rare in Cheddar cheese of greater than 5% S/M; there must also be a high population of starter lactococci and these lactococci must have a particular type of peptidase that produces hydrophobic peptides. Additionally the presence of certain non-starter lactic acid bacteria, NSLAB, can prevent bitterness due to their ability to degrade the hydrophobic peptides produced by lactococci. These can be naturally present in some cheese plants. When you take these factors into consideration, along with the natural variations that can occur in fat content in cheese readers will start to gain an appreciation of what is involved in the development of bitterness in cheese.

Control of bitterness starts with adjusting the cheese manufacturing conditions to ensure that salt levels are correct for the variety being manufactured, ensuring that ‘non-bitter producing starters’ are used and adjusting manufacturing to control starter populations. Many cheese makers also use starter adjuncts. The most effective for debittering contain strains of Lactobacillus helveticus that produce peptidases active against the bitter peptides. Note only some strains of Lactobacillus helveticus have a proven antibittering effect.

Some culture suppliers will have tested their starters for bitter peptide production, there are several test methods available, and may have strains of Lactobacillus helveticus that have been proven to be effective in cheese trials. Incidentally there are a number of well characterised Lactococcus lactis subsp cremoris strains that rarely produce bitter cheese; these are available commercially. Your culture supplier should therefore be part of your problem solving team!

Though not well publicised, for commercial reasons, blends of thermophilic starters along with lactococci are being increasing used in both Cheddar and Gouda manufacture. There is some anecdotal information suggesting that use of these starter blends results in less bitterness problems.

Q: Guidelines for salt intake
The Food Standards Agency (FSA) has produced guidelines for salt intake. Why might these be of significance to cheese manufacturers and retailers?

A: It has been known for some time that high sodium chloride(salt) intake can result in hypertension (high blood pressure) in sensitive individuals. The health risks associated with hypertension are well known and include coronary disease and premature death.

Salt (in the form of sodium) in food has generated significant debate regarding the actual health benefits to the population as a whole by reducing salt levels in food, and this is continuing e.g. some 90% of the population may not be salt-sensitive. Nevertheless it is now UK policy to move towards a significant reduction in dietary salt. Since manufactured foods are a significant and sometimes hidden source this will impact on food manufacturers including cheese makers.

The Scientific Advisory Committee of Nutrition (SACN) published a report on salt and health in May 2003. Following publication, the Food Standards Agency (FSA) set targets to reduce the salt consumption in the UK from 9.5g to an average of 6g a day by 2010 with an interim target of 10% reduction (1g per person per day) by 2005/6, see http://www.food.gov.uk/.

The UK Diary Industry Association (DIAL) submitted plans to the FSA in February, 2004, indicating that manufacturers would evaluate the potential to reduce the salt content of processed cheese; and that DIAL would collaborate with suppliers of cheese cultures to investigate the possibility of using strains of organisms less tolerant to salt. DIAL and Dairy Crest have apparently agreed to work with members to establish a salt model specifically for cheese, setting targets for salt content for different cheeses.

Why is the salt tolerance of starters of significance in the debate on salt levels in cheese? Salt addition has the potential to decrease starter activity and can be used to prevent bitterness associated with growth to high cell densities for some starters. Note salt sensitivity is one of a number of factors involved in bitterness. Today's starter cultures are generally less sensitive to salt than the mixed strain cultures used in the past.

Salt in the form of sodium chloride is an essential ingredient in the manufacture of Cheddar cheese. See Ebook for more information. Providing pH, fat in the dry matter and moisture in the non-fat-free-substance are within acceptable limits then
good quality Cheddar can be produced using salt-in-moisture values (%) ranging from around 4.0 - 5.9. This means that there is potential for Cheddar manufacturers to reduce salt levels. This can be done using good salting systems and careful use of mellowing time. Since some 33% of the sodium can be replaced with potassium, note food grade potassium chloride is several times more expensive than sodium chloride, there is some potential for replacing sodium with potassium and producing salt-reduced cheeses.

Manufacturers should understand that there is significant anti-salt lobby and that this is exercising significant pressure to reduce salt concentrations in food. Where salt is essential for the manufacture of the product, manufacturers should be prepared to explain the reasons for salt inclusion. Sea water contains around 2.6% (w/w) salt and manufacturers should be prepared to counter comments relating to drinking sea water if they market products containing this concentration of salt. Bacon and ham frequently contains salt concentrations around 2.6%.

Note that the guidelines for salt intake (maximum quantities, lower intakes are encouraged) are age-dependant:

1 to 3 years - 2 g salt a day (0.8g sodium)
4 to 6 years - 3g salt a day (1.2g sodium)
7 to 10 years - 5g salt a day (2g sodium)
11 and over - 6g salt a day (2.5g sodium.

Since manufactured foods are a significant, over 75 % of the intake in the US, and sometimes hidden source of salt the pressure to reduce salt in food will continue and this will continue to impact on food manufacturers.

There is a calculator for converting sodium to salt and determining the salt contribution from an individual meal to the recommended maximum daily intake for infants, children and adults at http://www.dairyscience.info/newCalculators/sodium.asp .

Q: Effect of mellowing on yield and quality
Explain how mellowing can influence cheese composition and yield?

A: Consider for a moment a dry-salted cheese like Cheshire. It is possible to visualise a ‘freshly’ produced block of cheese as comprising a multitude of small ‘cheese islands’ or ‘mini cheeses’ formed from the compression of individual curd particles.

These curd particles have previously been salted. The dry salt placed on the cheese curd partially dissolves in the surface moisture giving a thin layer of supersaturated brine. This brine solution initially causes shrinkage of the outer layers of the curd particle and whey moves from the interior of the particle to the periphery. This whey dissolves the remaining salt crystals effectively reducing the overall salt concentration in the brine coating the curd particle. The s/m gradient between the brine and the moisture in the interior of the curd particle results in movements of salt and moisture in opposite directions in response to their respective concentration gradients.

If the curd has been salted uniformly, salt equilibrium in an individual cheese island or mini-cheese can be calculated to take around 24 hours.

If the curd has not been salted uniformly then one can visualise pockets of curd of varying salt concentration in the vat. After pressing, there will be a multitude of mini-cheeses of widely differing salt concentrations. Under these circumstances, a block of cheese will consist initially of areas of low, intermediate and high salt concentration. While an overall equilibrium value for salt in the finished cheese will eventually be obtained, significant variation in salt concentration through a block of this cheese will be apparent for a considerable time.

For more information please see Casserly, F.M., Mullan, W.M.A. and Weatherup, S.T.C. (1994). The use of statistical methods to optimise yield in Cheddar cheese plants. In 'Cheese yield and factors affecting its control - Proceedings of IDF Seminar held in Cork, Ireland', p367-374. International Dairy Federation, Brussels (Belgium).

In modern cheese manufacture there can be a tendency to reduce mellowing times; this is not advisable and this author would recommend a minimum mellowing time of 20 min.

NOTE!!! The above is a simple non-mathematical explanation of a complex issue.