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Section E: Manufacture, Ripening, Process Control and YieldEfficiency

9. CHEESE MAKING STEP BY STEP

This chapter describes the principal steps involved in cheese manufacture. Tables 9.1 and 9.2 are sample process (make)and quality sheets.

9.1 Ripening the Milk

This term is a little confusing because it is also used to describe the ripening or aging of cheese. Here, ripening, refers to thepractice of giving the culture time to begin acid production before the rennet is added. This is done for two reasons:

To ensure the culture is active before the milk is renneted. It is impossible to inoculate after the milk is set. Normally, 45 -60 min is sufficient to decrease pH by 0.01 units or increase TA by 0.005 - 0.01%Development of acidity aids the coagulation process, especially the secondary stage.

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In some varieties such as brine brick and Swiss, low amounts of culture are used and renneting proceeds with little or no priorripening.

9.2 Setting the Vat

Handling Rennets

Repeatable performance depends on accurate measurement. For most varieties the quantity of rennet is selected to setthe milk to a firm coagulum in 30 - 40 min. Measure the rennet accurately and monitor to ensure that coagulation rate isuniform from day to day.Rennet must be diluted (about 20 times) in water and well mixed when added to ensure uniform distribution.Use nearly the same dilution each time to improve the consistency when adding the diluted rennet to the vat.Watch out for chlorine. It is imperative that the dilution water contains no chlorine. Only 2 ppm of chlorine will destroy 40%of rennet activity in 3 minutes. Similarly, do not sanitize the container used for the rennet with chlorine.Another water quality issue is pH. Typically hard water also has pH greater than 7.0 which also decreases rennet activity.Finally, dilute immediately before adding the rennet to the vat. After the brined rennet is diluted in water, its activitydeclines quickly.

Optimizing setting parameters

Milk preparation was discussed in Chapter 5. Here are the principal considerations:Pasteurization temperature: higher temperatures increase yield by increased recovery of whey proteins, but asuggested maximum with respect to curd quality is 75C, 16 s.Temperature history: if the milk is pasteurized and immediately sent to the setting vat, it will be necessary to adjustthe mineral balance by adding calcium chloride.

The jury on selection of coagulant always seems to be out. I tentatively suggest that microbial coagulants are notadvisable for high temperature varieties for reasons of heat stability, and not advisable for other varieties unless othersetting and conditions are under tight control. The preferred choices, then, are rennet and recombinant rennet.

The amount of rennet must be carefully determined. Because rennet is costly, it is desirable to minimize its use, but thiscan be false economy if curd properties are compromised. Poor setting means increased losses of both fat and proteinas fines.

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Temperature control must be accurate and uniform through out the vat, because both the enzyme activity and thesubsequent process of micelle aggregation are extremely temperature sensitive. Inaccurate or nonuniform temperatureduring setting will result in local areas of under or over set curd which in turn causes loss of fines during cutting.Soft curd results from:

Over heat treatmentLow setting temperatureHomogenizationColostrum or mastitic milk

Firm curd results from:High calciumLow pHStandardisation to high protein content.

9.3 Cutting The Curd

Proper cutting is extremely important to both quality and yield. Improper cutting and handling the curd results in the loss of fines,that is, small curd particles which are not recovered in the cheese. Unlike whey fat, fat trapped in fines; is not recovered bywhey cream separation. Therefore, both fat and protein losses occur when shattered curd results in fines too small to berecovered in the cheese.

Determination of curd cutting time

Both early cutting when the curd is fragile and late cutting when the curd is brittle cause losses of fines. Several means areused to determine cutting time.

Manual testing. The curd is ready to cut if it breaks cleanly when a flat blade is inserted at 45o angle to the surface andthen raised slowly.Several mechanical devices based on oscillating viscometry, thermal conductance and sonication have been testedexperimentally.Some plants cut by the clock. This may be OK as long as all conditions are uniform from day to day (is that every true??)and adjustments are made for any change in milk composition or properties.If setting temperature is high as for Swiss types, the curd firms rapidly and cutting must begin early when curd is stillsomewhat soft to prevent over setting. Agitation should begin immediately to prevent matting.





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Curd size

Curd size has a great influence on moisture retention. Hence, there is an obvious relationship between cheese moisture andthe prescribed curd size:

High temperature and low moisture varieties such as Italian hard cheese require the smallest curd. Cutting continues untilthe curd cutting is the size of rice grains.Medium moisture cheeses like most washed varieties and Cheddar are cut to Omega cm cubes.High moisture varieties like soft ripened cheese are cut with 2 cm knives or the curd is simply broken sufficiently to bedipped into forms.

Small curd size will result in greater fat and SNF recovery because large curds tend to get crushed resulting in the loss of'fines'. Smaller curds will also dry out faster and, therefore, other factors such as cooking temperature and stirring out may haveto be adjusted according to curd size.

Manual cutting

Manual cutting is done with cutting harps, made by stretching stainless steel wire over a stainless steel frame. Total cutting timeshould not exceed 10 minutes (preferably less than 5 minutes) because the curd is continually changing (becoming overset)during cutting. The knives should be pulled (not pushed) quickly through the curd so has to cut the curd cleanly.

Automated cutting

With mechanical knives, curd size is determined by the design of the vat and agitators, the speed of cutting (rpm) and theduration of cutting. In Double 'O' vats for Cheddar and American varieties, cutting is normally at a speed of about 4 rpm for 7 -13 minutes, corresponding two a total of 30 to 50 revolutions. It is important that the knives are sharp and cut the curd cleanlyrather than partially mashing the curd or missing some pieces altogether.

There is evidence (Johnston et al 1991, J. Dairy Res. 58:345) that curd particle size at draining in mechanized Cheddarcheese is influenced by cutting time, cutting speed, and subsequent agitation such that:

Short cutting times and low rpm result in small particle size at draining and larger losses of fines.





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With increasing cutting time (more total revolutions), curd particle size at draining reaches a maximum whichcorresponds to a maximum in fat recovery.Further increased cutting time causes decreased curd size at draining with little effect on fat recovery.

Healing

Curd should be agitated gently or not at all after cutting to prevent formation of fines. The exterior of the freshly cut curd is fragileso some time is needed for the edges to close up (heal) and prevent the loss of fat and protein to the whey.

An index of cutting quality

The loss of fines is best monitored by accurate analysis of whey fat content. Whey fat for Cheddar types should be <0.3%;.Efficient operations may achieve levels near 0.2%.

9.4 Cooking

The combination of heat and the developing acidity (decreasing pH) causes syneresis with resulting expulsion of moisture,lactose, acid, soluble minerals and salts, and whey proteins. It is important to follow the cooking schedule, closely. Cooking tooquickly causes the curd to shatter more easily and forms a tough exterior on the curd particles which prevents moisture releaseand hinders development of a smooth texture during pressing.

9.5 Draining

Most cheese is drained in the range of whey pH 6.1-6.4 (curd pH 6.0 - 6.3). Draining time should be uniform at about 20 min toprevent variation from vat to vat. Cheddar types may be stirred out 1 to 3 times as required to obtain required curd moisture.

9.6 Washing

Lactose content can be adjusted by moisture removal (syneresis), fermentation, or leaching with water. By leaching lactosewith water it is possible to make a high moisture cheese (such as brine brick or Muenster) and still achieve a final pH of about5.0 - 5.2. The temperature of the wash water will determine the moisture content of the curd. Sometimes relatively hot water(eg., Gouda) is used to dry the curd and develop its texture.





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Traditionally washing was accomplished by removing Omega to 2/3 of the whey and replacing it with water and agitating forabout 15 min. This process results in the dilution of large amounts of whey which must be reconcentrated or dumped. It alsocreates problems where curd tables have less capacity than setting vats. The solution is to remove more whey and add lesswater.

9.7 Curd Handling

Most brine or surface salted varieties are dipped directly into the forms or pressed under the whey. In the absence of salt, thecurd is fused to form a smooth, plastic mass. The hoops are turned at regular intervals to promote uniform drainage,symmetrical shape, and a smooth finish.

Some varieties such as Gouda and Swiss are pressed under the whey before draining. This encourages formation of smoothtexture and prevents incorporation of mechanical openings in the cheese due to trapped air or pockets of whey.

For Cheddar, American, and Pasta Filata varieties the curd is kept warm in the vat or drain table and allowed to ferment to pH5.2 -5.4. Pasta Filata varieties are then worked in warm water while Cheddar and American varieties are salted in the vat.

9.8 Pressing

Pressing varies from little or none for soft cheese up to 172 kPa for firm Cheddar cheese. The warmer the curd, the lesspressure required. Mechanical openings may be reduced by vacuum treatment before, during or after pressing.

9.9 Salting

Almost all cheese is salted by one of three methods: before pressing as in Cheddar and American varieties, surface saltingafter pressing, or brine salting.

Purposes of Salting

Promote further syneresisSlow acid developmentCheck spoilage bacteria. Lactics are more salt tolerant than pathogens and spoilage bacteria.Promote controlled ripening and flavour development.Salty flavour





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Brine salting:

Concentration 16 - 25% NaClTime:

20 kg cheese, 5 days or sometimes several weeks

3-5 kg, 24 h

250 - 350 g, 1 - 4 h

New brine should be treated with about 0.1% of CaCl2 to prevent conversion of calcium and hydrogen caseinate tosodium caseinate. The latter has high water holding capacity, so the cheese takes up water from the brine and thecheese surface becomes soft and slimy.Brine pH should be adjusted to the pH of the cheese. Normally a pH of 5.2 - 5.6 is adequate.

If the pH is too high, ion exchange causing sodium caseinate is encouraged.If the pH is too low, there is insufficient Ca/Na exchange and the cheese is too hard and coarse.

Brine must be cleaned regularly by filtration, preferably microfiltered. UV sterilization combined with filtration is also used.Brine must be continuously agitated to prevent density fractionation (lower concentration brine on top) and dilution of thebrine around the cheese.If cheese is floated rather than immersed in the brine, the exposed surface of the cheese should be dry salted.

Vat salting

For vat salted cheese, uniform salt content depends on accurate estimate of the weight of unsalted curd, accurateweighing of salt, and consistent processing conditions.Salt uptake is:

Increased by increased acidity (lower pH) at salting.Decreased by increased time between milling and salting due to healing of the cut surfaces on the curd particles.Increased by increased curd moisture content.Decreased for larger curds.

For Cheddar and American varieties the salt content as a percent of moisture (S/M) should be greater than 4.0%.





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Table 9.1 Record of Manufacture





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Table 9.2 Record of Quality Control





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10. RIPENING AND PACKAGING

10.1 Ripening processes: chemical and physical changes

Cheese ripening is basically about the breakdown of proteins, lipids and carbohydrates (acids and sugars) which releasesflavour compounds and modifies cheese texture. The biochemical and biophysical processes involved have only partly beenelucidated. Here we include only a few practical principles of ripening.

General Principles

Ripening varies from nil for fresh cheese to 5 years for some hard ripened cheese. Like a good wine, a good agedcheese should get better and better with age.Ripening processes are broadly classified as interior and surface ripened.

Cheese which depend mainly on interior ripening (most hard ripened cheese such as Cheddar and Italian types)may be ripened with rind formation or may be film wrapped before curing. Having said that, I hasten to add, thattraditional Italian types are always rind ripened. Cheddar and American varieties are the only ripened cheeseswhich (in my view) are not drastically altered by film wrapped curing.Cheese which depend mainly on surface ripening include smear ripened and mould ripened

In the broadest terms there are three sources of cheese flavour:Flavours present in the original cheese milk, such as natural butter fat flavour and feed flavour.Breakdown products of milk proteins, fats and sugars which are released by microbial enzymes, enzymesendogenous to milk, and enzyme additives.Metabolites of starter bacteria and other microorganisms. These include products from catabolism of proteins, fatsand sugars.

Flavour and texture development are strongly dependent on:

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pH profileCompositionSaltingTemperatureHumidityEXPERIENCE.

As a general rule factors which increase the rate of ripening increase the risk of off flavour development, and reduce theperiod of time when the cheese is saleable

Protein Breakdown (Proteolysis)

Natural degradation of protein is called 'putrefaction' and results in 'rotten potato' type odours, especially if high quality proteinssuch as animal proteins are involved. That's because animal proteins contain the essential sulfur amino acids. These'putrefactive' components are also the stuff of which good flavours are made. Protein degradation during cheese curing is adirected process resulting in protein fragments with desirable flavours.

Some off flavours associated with undesirable or excessive protein breakdown in cheese are bitter, stringent, putrid andbrothy.Protein breakdown causes shorter body which is less rubbery, less elastic, more meltable. For example, flavour andtexture development in Cheddar are mainly dependent on protein breakdown and much less dependent on fatbreakdown.Protein breakdown involves three general types of processes:

Proteases break proteins into smaller peptides, some of which are flavour compounds. For example, bitter andbrothy flavoured peptides are well known to occur in cheese.Peptidases further break down peptides to amino acids.Further catabolism of amino acids by cheese microorganisms produces aldehydes, alchohols, carboxlic acids andsulfur compounds, many of which are flavourful.

The amino acid, tyrosine, forms crystals in aged cheese such as Parmaggiano regiano, which are readily detected onthe palate.

Fat Breakdown (Lipolysis)





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Dairy fat is a wonderfully rich source of flavours, because it contains an extremely diverse selection of fatty acids. In particular,butter fat is the only natural fat which is rich in short chain fatty acids. Butyric acid for example is a potent flavour compound. Aswith all potent flavours the trick is to add just the right amounts in balance with other flavours. Here are a few principles:

Dairy fat without any ripening during cheese making is an important contributor to cheese flavour and texture:Fresh dairy fat has the well known 'buttery' flavour associated with extremely low levels of free fatty acids.Fat also acts as a flavour reservoir, so hydrophobic (fat soluble) flavours derived from protein breakdown arestored in the fat and released during mastication in the mouth.Finally, fat is an important component of cheese softening and melting.

The fat derived flavours associated with cheese ripening result from the release of fatty acids by lipolysis and furthermodification of fatty acids by microorganisms to other compounds.Varieties traditionally made from goats' milk have higher levels of lipolysis.Blue moulds are generally quite lipolytic

Lactose

Milk contains no starch or fibre or any sugar other than lactose so all carbohydrate compounds in cheese are derived fromlactose or produced by microorganisms. Relative to fat and protein lactose contributions to flavour are minimal. Here's a fewprinciples:

At Day 1 following cheese manufacture most of the milk sugar has been removed in the whey by or by fermentation, thatis converted to lactic acid by the cultures.Residual lactose depends on the type of cheese and other factors. For examples:

High salt in the moisture phase of Cheddar slows lactose metabolism so lactose content is .3 to .7%% at one dayafter manufacture and slowly declines to less than 0.1%.Residual lactose in Camembert cheese is used by Penicillium camemberti so it decreases quickly, especially onthe surface, when the mould begins to grow.In well drained cheese such as Swiss types, lactose is completely used up in a few hours.In washed cheese varieties, lactose not leached by washing is quickly used up by the culture, especially for Dutchtype cheese where salting is delayed. In Colby, early vat salting reduces the rate of utilization of residual lactose.

Many organisms, including yeasts and moulds in mould and smear ripened cheeses utilize lactate and produce variousflavourful compounds.Calcium salts of lactic acid may form white precipitates on the surface of aged cheese.





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10.2 Principal Ripening Agents

Milk Enzymes

Plasmin: A milk protease which survives pasteurization and breaks down caseins during cheese ripening.Particularly important in Swiss type cheese.Inhibited by Beta-lactoglobulin, so it has minimal activity in cheese made from ultrafiltered milk.

Lipoprotein lipase is the principal milk lipaseInactivated by low heat treatment but is important to flavour development in raw milk cheese

Milk Coagulant

Each milk coagulant has its own proteolytic profile (see section on coagulants).Purified extracts produce more consistent flavours but lack character.For aged cheese no enzyme other than calf rennet and recombinant calf rennet has proven fully acceptable.Rennet and recombinant rennet actively break down alpha-casein but do not break down beta-casein in cheese.

Lactic Cultures

During the early days and weeks of ripening, LAB numbers decrease while the numbers of nonstarter bacteria decrease.For example, in Cheddar cheese, LAB counts reach a maximum (up to 500 million per gram) within 3-4 days and thendecrease to about 20 million at 4 weeks. However, the dying cells release enzymes which continue to ripen the cheese.Lactic cultures contribute to proteolysed flavours but are minimally lipolyticHeterofermentative cultures ferment citrate as well as lactose and contribute both flavour (diacetyl) and carbon dioxide forsmall eye development

Secondary Cultures

In Swiss types, carbon dioxide production by Propionibacterium is encouraged by exposure to 200C for about 3 weeksafter brining and drying off in the cold room.For smear ripened cheese, Brevibacterium linens , coryneform bacteria, and yeasts are encouraged by high humidity(90-95%) and washing to discourage mouldsPenicillium sp. for Camembert, Brie and Blue types require 85-90% humidity and air circulation to provide oxygen





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Non-starter Microorganisms

Microorganisms present in the milk due to environmental contamination are important contributors to milk ripening. Someimportant facts are:

Bulk cooling and storage of raw milk selects for cold tolerant (psychrotrophic) bacteria (see Chapter 3).Heat treatment selects for thermal stable spore forming bacteriaNon-starter bacteria commonly present in heat-treat Cheddar include Lactobacillus sp. and Pediococci sp.Many other bacteria and yeasts may be present and may or not grow depending on complex symbiotic relationships withother bacteria.Heat treat is really a process of standardizing the nonstarter microorgansims, namely, eliminate proteolyticpsychrotrophic bacteria but retain a range of useful ripening microbial agents.Non-starter bacteria in cheese milk can be reduced by microfiltration.

Added Ripening Agents

Addition of lipases as noted earlier is common for Italian and other cheese varieties. The principal areas of continuingdevelopment are:

Accelerated ripening agents for all ripened cheese, especially CheddarRipening agents for low fat cheese, again especially Cheddar.The principal approaches are:

Direct addition of single enzymes of dairy or non-dairy sourcesEnzyme cocktails which are mixtures of proteases and lipases. Other than in the preparation of enzyme modifiedcheese pastes, enzyme cocktails have had limited commercial success.Enzyme capsules which release trapped enzymes during ripening.Attenuated (freeze shocked or heat shocked) proteolytic culturesGenetically modified cultures hold lots of promise for future success.Culture adjuncts such as Lactobacillus helveticus in Cheddar cheese hold much promise to replace the normaldiverse microflora of raw milk.

10.3 Cheese Composition for Optimal Curing

Cheese composition is critical to yield optimization, and both flavour and texture development. This section gives some detailon several critical composition parameters, with special reference to Cheddar cheese. New Zealand export Cheddar cheeseis all graded by composition analysis as indicated in Figure 10.1 A. Figure 10.1 B indicates the ranges which are typical of

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is all graded by composition analysis as indicated in Figure 10.1 A. Figure 10.1 B indicates the ranges which are typical ofgood Canadian Cheddar

MNFS

Moisture: higher moisture means faster ripening which means more potential for off flavours and over ripening.water activity (aw) decreases with age because ripening results in many soluble breakdown products of acids, sugars,proteins and lipidsfresh Cheddar aw = 0.98 which is conducive to most bacteriaaged Cheddar aw as low as 0.88 which is too low for most bacteriaMNFS is a better index of cheese ripening potential than % moisture

Optimum MNFS depends on expected date of maturity and curing temperatures:

examples for Cheddar: 100C, 6-7 months MNFS = 53%

100C, 3-4 months MNFS = 56%

MNFS is controlled mainly by pH at dipping and cooking treatments. Subsequent curd treatment such as cheddaring andsalting also influence MNFSMNFS is also influenced by FDM. Other conditions being kept constant, MNFS increases with increasing FDM, becausefat inhibits syneresis.

S/M

Determines rate of acid development during pressing and early curing and, therefore, influences the minimum pHAffects bacterial profile, eg., high S/M will discourage contaminating bacteria such as coliforms.Critical to rate of proteolysis and the type of protein derived flavoursAcceptable range is broad (3.6 - 6.0), fortunately because S/M varies widely even within a single cheese.Salt uptake is affected by quantity of added salt, size of curds, moisture content of curds, and acidity

FDM





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Higher fat restricts syneresis, so MNFS tends to increase with FDMFat shortens and softens cheese texture because the fat globules physically disrupt the protein matrix.Adjusted by milk P/F (See Chapter 5)

pH

The pH profile is the single most important trouble shooting tool. Critical points are: cutting, draining, milling, 1 day and 7daysMost cheese including Cheddar should reach a minimum pH of 5.0 to 5.1 during the first week after manufacture;obtaining a final pH in this range is greatly helped by increased buffer capacity of milk proteins in the pH range 5.4 - 4.8.Factors determining the pH at one day are amount of culture, draining pH, washing, curd treatment such as cheddaringand salting.Draining pH is most important to cheese texture and also determines residual amounts of chymosin and plasmin in thecheese.pH increases with age due to release of alkaline protein fragments. This is especially true of mould ripened cheeses.Camembert pH increases from 4.6 to 7.0, especially on the surface.Increasing pH during curing encourages activity of both proteases and lipases

10.4 Temperature of Curing

Cheddar types: 4 - 10C, 8-10C is the recommended range. It is desirable to initiate ripening for several weeks at 4-6Cand then increase the temperature to 8 - 10C. Low temperature initially, minimizes early growth of starter and non-starterbacteria and reduces the risk of too rapid ripening and off flavour development. It also minimizes the risk of the minimumpH reaching levels below 5.0.Most European varieties are stored at 10 - 15C for initial ripening and then 4C until consumed.Surface ripened varieties are ripened at 11 - 15C.

10.5 Humidity of Curing

Surface ripened cheese also require adequate air circulation to provide sufficient oxygen for moulds and yeasts. Humidityrequirements in general are:

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Washed bacterial surface ripened: 90-95%Fungal flora: 85-90%Dry rinds: 80-85

10.6 Ripening Treatments

According to the type of surface characteristics, cheese treatments are grouped as follows:

Ripened by surface mouldsWashed rinds with out (or with little) bacterial growth, e.g., St. Paulin types.Washed rinds with smear, e.g., Muenster types and OkaDry rinds which may be coated with oil or butter to prevent cracking and desiccation, e.g., Edam, Scamorza, andParmesan.Waxes and resins which may be applied by dipping, brushing or spraying. These provide good protection but are morepermeable than plastic films, so it is still desirable to maintain 85% RH to prevent drying.Rindless cheese which are cured in moisture and gas impermeable film or in large blocks (eg., 640 lb Cheddar)

Waxes and films may be treated with anti-mould agents such as pimaricin, sorbic acid and propionates to prevent mouldgrowth.

10.7 Packaging

Vacuum and/or gas flush (N2 and CO2) in gas and moisture proof film are common.Vacuum alone is not recommended because complete evacuation of oxygen is difficult and small unsightly mouldspots often appear.Gas flush with CO2 or blends of CO2 and N2 effectively prevent mould growth.

CO2 is water soluble so it is absorbed into the water of the cheese and the package becomes tight.N2 which is not water soluble is useful for applications, such as shredded cheese and cheese curd, where aloose package is desired.





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High density plastic (rigid containers) are used for fresh cheese such as cottage.Oxygen permeable wrap such as grease proof paper and foil-laminated but unsealed wraps, are preferred for surfaceripened soft cheese

Figure 10.1 Cheddar cheese composition for optimum curing. (A) New Zealand standards for Premium and FirstGrade Cheddar cheese. (B) Typical ranges for high quality Canadian Cheddar. Note: pH measured between 3 and14 days after manufacture.





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11. PROCESS CONTROL

This Chapter will not be discussed during the short course lectures because most of its contents are covered in other Sectionsor in the cheese make procedures. It is included here as a summary of important process control principles.

11.1 The Objectives of Cheese Manufacturing

To maximize returns, the cheese maker must obtain the maximum yields which are consistent with good cheese quality. Forexample, water and salt are cheaper than milk fat and protein, but you can only have so much cheese moisture and salt---moreon cheese yield in Chapter 12. With respect to consistent production of high quality cheese the objectives of the cheese makerare to:

(1) Develop the basic structure of the cheese.

(2) Obtain cheese composition required for optimum microbial and enzyme activity during curing. Optimum composition mainlymeans optimum levels of moisture, fat, pH (lactic acid), minerals, and salt.

For example, the characteristic texture of Swiss cheese is largely determined at the time when the curd and whey aretransferred to the press table. At this time the basic structure (i.e., the manner in which the casein micelles and fat globules arearranged) and chemical composition (especially mineral content) is already determined. You can not take Swiss curd at thisstage and make Cheddar cheese. On the other hand it is possible to produce both Feta and a Brie type cheese from the samecurd.

11.2 Moisture Control

cheese making is a process of removing moisture from a rennet coagulum or an acid coagulum consisting of fat globules(unless the milk is skimmed) and water droplets trapped in a matrix of casein micellescheese is, therefore, a concentrate of milk protein and fat.





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most cheese making operations are related to this process of removing water from the milk gel by the process ofsyneresissyneresis = to contract; refers to contraction of the protein network with the resulting expulsion of water from the curdthe water and water soluble components are literally squeezed out of the curdthis liquid, (whey) contains water, sugar, whey proteins, lactic acid and some of the milk mineralsthe final moisture content, therefore, to a large extent determines the final pH of the cheese because it determines theresidual amount of fermentable lactose in the cheeseat the same time other factors such as the amount and rate of acid development and the temperature and time ofcooking, determine the amount and the rate of syneresis

11.3 pH Control

with respect to cheese quality and safety, the most important process control factor is the development of acidityincreasing acidity causes:

-syneresis (due to reduced charge repulsion on casein micelles) and moisture expulsionsolubilization of calcium phosphatesdisruption of casein micelle structure with alterations in curd texturereduced lactose content by fermentation to lactic acid

acid development occurs mainly within the curd because most bacteria are trapped in the gel matrix during coagulationfinal pH (acidity) is dependent on the amount of acid developed during manufacture and the residual lactose which willferment during early curing and cause further acid developmentthe residual lactose content is mainly determined by the moisture content, washing which removes lactose by leaching,and the extent of fermentationability of culture to ferment galactose is also importantboth the rate of acid development and the amount of acid development (as measured by final pH) are importanteg., final pH of Swiss is the same as Cheddar but Cheddar cheese reaches pH 5.2 after about 5 hours while Swisscheese requires about 15 h to reach this pHit is important to maintain uniform rate of acid development; if acidity develops too slow or too fast, adjust the amount ofculture rather than changing cooking time or temperaturepH at draining largely determines the mineral and residual sugar contents of the cheese and from the sugar, the final pHsalting reduces the rate of acid development, and, therefore, the time and amount of salting is important to the pH at 1day and 7 days following manufacture





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11.4 Mineral Control

loss of calcium phosphate determines extent of casein micelle disruption--hence it determines basic cheese structure;the important parameter is the ratio of Ca to casein or Ca to SNF which is easier to measure (See Table 1.1)in Swiss (high Ca, about 750 mM Ca/kg SNF) micelle globular structure is intact while extensive dissociation anddisruption of submicelles is evident in Feta types (low Ca, about 400 mM Ca/kg SNF))retention of calcium phosphate in the cheese also increases the buffer capacity of the cheesepH at draining determines the solubility of calcium and phosphate when the curd is separated from the wheymore Ca is retained at high draining pH as in Swiss cheese (pH 6.4 - 6.5) versus Cheddar 6.1 - 6.3 (See Table 1.1).little Ca retained in Feta cheese which needs some explanation:

Feta is dipped into the forms early while the pH is still quite high. However, the moisture is also high because no cookinghas taken place. Therefore, the moisture is removed by syneresis as the pH decreases while the cheese is in the forms.The net result is that a great deal of moisture (whey) is removed at low pH and most of the calcium phosphate is removedwith it. This is also true for other soft ripened cheese like blue and camembert.

11.5 Texture Control

untypical texture in a young cheese is a strong indication of probable flavour defects later; therefore, a primary objectiveof cheese making is to develop the ultrastructure which will determine the proper textureconformation of the protein matrix is also influenced by pH--at lower pH micelles are disrupted, but the proteins are tightlypacked because of reduced charge repulsion; therefore, Feta is brittle while Camembert is soft and smooth due toalkalinity contributed by ammonia during ripeningcheese drained at higher pH has higher calcium content and is firmer and more elasticfirmness is also affected by ripening agents (see 11.6 Flavour control)other factors also play a role--salt, moisture, and fat, but none of these will alter the basic structure of the protein matrix atthe submicellar level.

11.6 Flavour Control

milk heating and clarification treatments which determine non-starter bacteria present in the milktypes of cultures and coagulating enzymesall cooking and curd handling procedures have specific effects on the types of ripening agents (bacteria and enzymes)

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which remain to ripen the cheese; especially in cheese such as Swiss where the composition and functions of the cultureare more complexpH at draining again important because it determines the distribution of plasmin and rennin between the curd and thewheyplasmin is the principal milk protease: it prefers neutral to slightly alkaline pH and is more soluble at low pH; therefore,cheese which are dipped at high pH have higher retention and activity of plasmin (eg., in Swiss protein breakdown duringripening is due to plasmin)calf rennet is more soluble at higher pH but more active at lower pH; therefore, an acid cheese such as Feta or Cheshire,has more rennet activity than Cheddarthe solubility of microbial rennets is independent of pH

11.7 For example ....

The following charts illustrate how a cheese maker may adjust process parameters to make cheese with differentmoisture and ripening targets.

Table 11.1a Pasteurized Milk Cheddar Cheese (also for Heat Treatment Milk) - Record of Manufacture





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Table 11.1b Raw Milk Cheddar Cheese - Record of Manufacture





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Table 11.1c High Moisture Cheddar - Record of Manufacture





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12. YIELD EFFICIENCY

12.1 Distribution of Components During Cheese Making

TABLE 12.1. Distribution of milk components during cheese making (% by weight) and percent transfer from milkto cheese.

Fat Protein CHO AshSolidsMilk composition %

Cheese composition %

Whey Composition %

% Transfer

3.3 3.2 5.0 0.7 12.4

31 25 2.0 2.1 60

0.22 0.61 5.3 0.58 7.0

93 78 4 30 49

12.2 Factors Affecting Yield

Milk casein is the principal yield determining factor. Casein contributes absorbed water and minerals as well as its ownweight. Cheese quality limits the ratio of moisture/casein, a ratio which corresponding to MNFS.Fat is also a principal yield component. Fat interferes with syneresis and, therefore, also contributes more than its own


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weight, but if other conditions are adjusted to maintain constant MNFS, then fat contribution to yield is dependent only onthe conversion factor of fat from milk to cheese (i.e., fraction of milk fat recovered in the cheese).Cheese moisture. A 1% increase in Cheddar cheese moisture causes about 1.8% increase in cheese yield, partlybecause more moisture means more whey solids and salt are recovered in the cheese (eg., given 90 kg cheese/1000 kgmilk, a moisture adjustment to 36% would result in 91.6 kg cheese/1000 kg milk)Cheese salt. An extra 0.1% salt means an extra 0.14% yield of Cheddar cheese if the moisture content is increasedaccordingly.Milk quality factors: somatic cell counts, psychrotrophic bacteria, protein quality etc. See Chapter 4.Increasing time and temperature of milk pasteurization increases cheese moisture retention and the recovery of wheyproteins and soluble solids. There doesn't seem to be any consensus on how much is desirable but it's safe to say that itdepends on the type of cheese and the quality standards of the manufacturer.Process control parameters (See Chapter 9)

Careless cutting.Heating too fast at early stages of cookingSalting too soon after milling of Cheddar allows rapid salt uptake which in turn causes rapid synerisis andincreased solubility of casein. Yield is, therefore, reduced by losses of protein, fat and soluble solids.High temperatures during pressing cause loss of fat.Proteolytic cultures or coagulating enzymes cause protein losses before and after cutting.Washing removes soluble solids.Working as in Mozzarella removes fat and soluble solids. Loss of soluble solids is minimized by equilibration of thewash water with the cheese moisture.

12.3 Principles of Yield Optimization

With respect to yield the cheese maker's objectives are to:

(1) Obtain highest MNFS (moisture in non-fat substance) consistent with good quality to maximize moisture and the recovery ofwhey solids

(2) Standardize milk to obtain maximum value for milk components consistent with good quality (eg., adjust P/F to maximizecost efficiency).

(3) Minimize losses of fat and casein in the whey


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12.4 Yield Control

It is absolutely vital to be able to measure and maximize yield efficiency. This means maximizing the return (or minimizing theloss in the case of lactose) from all milk components entering the plant. This includes obtaining maximum returns for whey non-fat-solids, whey cream and cream skimmed during standardization. In general the highest return for all milk components, isobtained by keeping them in the cheese, but this may not always be the case.

12.5 Recovery of Milk Components

Yield efficiency can be determined by monitoring recovery of milk components and losses in the whey as recommended byGilles and Lawerence N.Z.J. Dairy Sci. Technol. 20(1985):205. By keeping accurate records of all incoming milk componentsand their distribution between cream, cheese, whey cream and defatted whey it is possible to determine the plant massbalance.

12.6 Yield Prediction

Purposes of Calculating Predicted Yields

(1) Provide a target against which to judge actual yields and determine mass balance within the plant

(2) Flag errors in measurement: eg. weights of milk or improper standardization etc.

(3) Early signal of high or low moisture content which allows adjustment on the following vats. This can be met by rapid moisturetests (microwave) which is sufficiently accurate for this purpose

The Van Slyke and Price Formula

The formula most often used for Cheddar cheese is the Van Slyke formula which was published in 1908 and has been usedsuccessfully ever since. The Van Slyke formula (Equation 12.1) is based on the premise that yield is proportional to therecovery of total solids (fat, protein, other solids) and the moisture content of the cheese.





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F = Fat content of milk (3.6 kg/100 kg)

C = Casein content of milk (2.5 kg/100 kg)

0.1 = Casein lost in whey due to hydrolysis of -casein and fines losses

1.09 = a factor which accounts for other solids included in the cheese; this represents calcium phosphate/citrate saltsassociated with the casein and whey solids

M = moisture fraction (0.37)

This formula has several important limitations:

First, it's difficult to measure casein. Many plants use total protein in the predictive formula and multiple by a factor toestimate casein. The classical procedure for casein determination is Rowland Fractionation which is too involved formost cheese plants. I recommend that two or three silo samples be sent to a private lab every 4 weeks to monitorseasonal variation in the casein fraction of protein. Alternatively the casein content can be estimated from the equationgiven in Chapter 6.A second difficulty is that the formula fails to consider important variables such as variation in salt content and wheysolids.Third difficulty is that the equation is quite specific to Cheddar.

Many other formulae have been developed and used. Probably the best proven formulae are those developed in Holland wherecommercial cheese manufacturers have been making good use of predictive yield equations for many years. Emmons et al.have developed a formula which has general application. See Emmons et al. Modern Dairy, Feb., 1991 and June, 1991;J.Dairy Sci. 73(1990):1365-1394. See also references listed in Chapter 2.

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13. DEFECTS AND GRADING

13.1 Defects

The following brief summary does not do justice to the existing body of knowledge and experience. Readers interested in moredetails on defects of surface ripened cheese are referred to Eck & Gillis, 2000.

Common Cheese Defects

Body. In the context of modern sensory analysis body refers to texture, which is confusing because cheese graders usethe term 'texture' to refer to cheese openness. Here, we will use the traditional cheese grading terms. Some descriptorsfor body defects are:

Crumbly/short: often due to excess salt or acidCorky: due to overcooking, low fat, low moisture, or excess salt.Mealy: this defect can be detected on the palate or by massaging the cheese between the thumb and forefinger. Itis usually associated with excess acidity.Pasty: sticks to the palate and fingers; due to excess moisture.Weak: breaks down too quickly when worked by hand; due excess fat or moisture.

Texture relates to openness in the cheese which may or may not be desirable depending on the type of cheese and thecause of openness. Openness can be due to:

Mechanical openings which are holes of irregular shape caused by trapped whey. Trapped whey makes theimpression in the cheese during pressing, but during ripening the moisture is dispersed through out the cheeseleaving the hole behind. Openness is desirable in Colby, but is considered a defect in Cheddar. Mechanicalopenings can lead to discolouration around the opening due to local acid development. Usually mechanical

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openings are closed by vacuum packaging.Gas holes are, of course, desirable in many types of cheese. Gas hole defects include:

Early gas defects due to coliforms. These appear as small, sphericle, shiny holes. The defect is oftenassociated with unclean flavour.Late gas due to Clostridium. tyrobutryricum or perfringens, especially in some European made cheese.Clostridia spores are often present in American cheese as well but do not normally cause problems.However, they may be activated by the heat treatment and, therefore, sometimes cause gas defect inprocessed cheese.A third gas defect occurs in Cheddar and American types. The defect is distinctive in that the gas (mainlyC02 with some hydrogen sulfide) blows the package but not the cheese. The defect occurs at 6 - 9 months inCheddar but a similar defect is sometimes observed earlier in American Mozzarella and Colby. Thecausative anaerobic organism is not fully identified, however, experiments have demonstrated that the defectdoes not occur in cheese aged at < 10C.Yeast slits due to yeast growth.

Flavour. Most grading systems assign the greatest weight to flavour defects. A few common descriptors are:Acid flavour is often associated with acid body defects noted above. The common causes all relate to processcontrol:

Too much moisture (i.e., too much lactose).Too much starter (i.e., too much acid development before dipping).Salting too late or too little.Too warm during or immediately after pressing.

Bitter flavours are common defects in American but also other cheese, including fresh cheese. Some causesinclude:

High moistureExcess rennetBitter culturesHigh ripening temperatures

Fruity/Yeasty flavours are usually associated with high pH and bitterness, and sometimes with yeast slits.Unclean flavours are reminiscent of the barn yard, and may be associated with coliforms.Whey taint is due to high moisture and is usually associated with acid defects including bitterness.

Colour. Other than traditional colour preferences such as orange cheddar and white goats' cheese, the most important





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colour parameter is uniformity. Even for cheese such as Colby which is coloured with annatto, graders do not evaluatecolour intensity. Rather, they look for nonuniformity which may signal a manufacturing defect. Here are some commondescriptors:

Acid cut (pink or bleached): low pH, oxidation of annattoMottled: may be an acid defect or caused by mixing cheese from different vats.Seamy: this is Cheddar defect where the curd particles fail to knit properly. Causes are:

Greasy curd from too much vat or high temperature during pressingImproper salting, too soon after milling or pH at salting is too high or too lowHooped too soon after salting

Finish. There is a lot of art and patience required to produce cheese with a good finish. Common defects are:Checked/Cracked: too dry on surfaceGreasy: temperature too high during pressing or curingHuffed: gassy

Mineral Deposits due to calcium lactateCommon on Cheddar cheese and sometimes on American varietiesEncouraged by certain non-starter Lactobacilli and Pediococci which favour formation of D-lactate which in turnencourages crystallization of DL-calcium lactate.Control measures are:

Decrease numbers of non-starter bacteria (eg., pasteurize versus heat treat and/or bactofuge the milk)Use tight packaging. Calcium lactate crystals tends to form in areas where the package is loose or indepressions on the cheese surface.Avoid temperature fluctuations. Calcium lactate crystals often form in the dairy case where temperatures arenot constant.Encourage rapid turn over in the dairy case.

Rind rot caused by mites or mould. Mites are almost unheard of in modern cheese making practice, but I have somegreat pictures





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Surface mould is definitely one of the most common defects. Indeed a frequent question to me, is about the safety ofeating mouldy cheese.

Unsymmetrical/Rough: poor workmanship

13.2 Grading

The following grading description and score sheets are included as examples only. The Agriculture and Agri-Food Canadaofficial scoring system for export Cheddar is described below. Also included is a typical score sheet used by the Canadianscoring system, and a general score card entitled "Cheese Judging Score Card" which can be used for any cheese variety.

Agriculture and Agri-Food Guidelines for Grading Cheddar Cheese

Standards - Canada Dairy Products Act.

Flavour 45

Texture 25

Closeness 15

Colour 10

Finish 5

Flavour - An ideal cheddar cheese should have a clean, mildly salty, nutty flavour and a pleasing aroma. The intensity of flavourvaries with age.

Body - The desirable body should be firm and springy, slightly elastic. The cheese should be smooth and waxy when crushedbetween the fingers. A slight weakness or coarseness may be permitted in first grade.

Closeness - The ideal cheese should be continuous and free from openings, cracks, breaks or fissures. A slight openness may





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be permitted in 1st grade. Slight gas holes in second grade and gas holes or Swiss holes are third grade defects.

Colour The colour should be uniform and translucent whether white or coloured. A slight seaminess may be allowed in 1stgrade.

Finish - The cheese should present an unbroken rind or symmetrical shape and a clean neat attractive appearance.

Notes:

1. Cheese should be held overnight at 14.5 - 15.5∞C before grading.

2. Cheese samples should be 9 kg in weight.

3. Cheese should be at least 21 days old before grading.

4. Early evaluation of aging potential can be obtained by grading a sample stored at 15∞C for 21 days.

Common Descriptors used in Grading Canadian Cheddar Cheese

Code - Total Score, Maximum 94

1. Sl. open, sl. stiff, sl. coarse, blurred branding, sl. damp end, sl mouldy surface.

2. As above plus slight acid tendency.

3. Weak, open, coarse, wet ends, sl. acid, sl. gas or pin holes, mottled colour etc.

4. Checked rinds with mould penetration. Sl. gas or pin holes. Any above defect plus a second defect except weak and open.

5. Very weak, very acidy, very stiff, very open, gas or Swiss holes (always 3rd), very uneven colour, very mottled.

6. Checked rinds, mould penetration, gas or Swiss holes (always 3rd).

Code - Flavour Score, Maximum 40

F1 Sl. unclean, sl. off, sl. fruity, sl. weak. sl. musty, sl. bitter, sl. sour.

F2 Sl. rancid, fruity, off, bitter, weed, sour, musty.





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F2 Sl. rancid, fruity, off, bitter, weed, sour, musty.

F3 Very fruity, rancid, badly off, very bitter, very unclean, very weedy.

Typical examples

Cheese Score

40 - 921 - A 1st grade cheese with no flavour defects but which has objectionable body defects such as (1) sl. open, sl. stiff, orblurred branding.

39 - 885 - A 2nd grade cheese with no flavour defects but which has objectionable body defects such as (5) checked rinds withmould penetration very weak or very acidy etc.

38(F1)-883 - A 2nd grade cheese with (F1) a sl. unclean, sl. off, sl. fruity, sl. weed, etc., flavour and with defective bodycharacteristics (2) open, weak or sl. acid.

36(F3)-865or6 - A 3rd grade cheese with (F3) very fruity, rancid flavour, etc. and has objectionable body characteristics (5 or 6)such as checked rinds with mould penetration or large gas holes, etc.

sl. - slight

Table 13.2 Cheddar Cheese Judging Score Card - Agriculture Canada Grading System





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14. SANITATION

The following are a few general comments about sanitation. A more detailed presentation on sanitation will be made by LarryKropf, DiverseyLever, Oakville.. Cheese makers are frequently too relaxed about sanitation because they assume that theactive cultures and development of acidity in cheese offer adequate protection against pathogenic organisms. It's true that wellmade cheese normally offers significant hurdles to most pathogens, however, several pathogens are well known to survive andmay grow under the conditions of cheese manufacture and curing (see also Section 4.5). Cheese with minimal aciddevelopment such as Latin American White Cheese (Queso Blanco) and cheese which undergo increased pH during curing(Brie, Camembert and, to a lesser extent, Blue) are especially susceptible to growth of pathogens.

1. Culture room

separate from plantpositive air pressuretotally clean at all timesrestricted access

2. Drains

must have trapsmust be adequate for peak periods to avoid any pooling of whey and/or wash water

3. Surfaces

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all food contact surfaces must be stainlessexceptions are curing boards and rooms for surface ripened cheese

4. Personnel

clean clothes, clean person, especially handsStaphylococcus aureus and fecal coliforms are often from people

5. Plant Environment

ideally have positive air pressureseparate raw milk operations from rest of the plantno implements or equipment or persons move from raw to pasteurized sectionscheck coliform counts of equipment and employees on regular basis

6. Cleaning Systems Depend on:

(1) Soil to be removed: fat, protein or milk stone

(2) Surface to be cleaned

note that stainless steel is not a smooth surface to the eye of the microscope nor to amicroorganismfrom the perspective of a coliform organism, a stainless steel surface is world of mountains andvalleys stretching out into infinitymechanical abrasion only further roughens the surface and makes cleaning those valleys moredifficultmust let the chemistry do its workchlorinated alkaline cleaners will remove both fat and protein if applied for sufficient timecheck vat surfaces with a flourescent light; if the surfaces reflect bluish/purple light you know thereis a residual protein film

Cleaning Action:

(1) Water rinse: removes loose soil

collection of first rinse, especially from milk storage tanks, will substantially reduce biological oxygen demand





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(BOD) loads in the drain

(2) Chlorinated alkaline detergent with chelator

detergent provides wetabilitychelator softens water and removes milk stonealkali swells and loosens proteinsrinsing action is then sufficient to remove soil

(3) Water rinse

(4) Acid rinse: nitric, phosphoric

complete removal of milk stone and water hardness

(5) Rinse

(6) Disinfectant

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