Paper 07: Technology of Milk and Milk Products

Module 27: Defects in cheese and cheese products

Introduction

Regardless of consumer preference, the flavor and textural qualities of cheese do influence the

value of cheese in the market place. When specific defects are present in cheese, the value of the

cheese is reduced and the consumer loses faith in the dairy plant’s product.

The occurrence of defects in natural cheeses can significantly influence the overall quality and

value. Some defects may be a result of poor milk quality or inadequate cheese making practices,

but they do not develop until the ageing of cheeses or during the distribution or marketing of the

cheese. Therefore, cheese makers must continuously evaluate their cheeses throughout the

ageing process and during marketing, if they want to effectively assess their cheese making

procedures and practices.

Table 1. Probable defects in cheese during manufacture – its causes and preventive

measures

No. Defect Causes Prevention

1. High moisture in cheese Slow acid development

Rapid scald

Insufficient scald

Poor whey drainage

Low pressing pressure/time

combination

Allow more acidity

Slower scald

Increase scald temperature and

time

Increasing pressing

pressure/time combination

2. Low moisture in cheese Low fat

Excess rennet quantity

Curd cut too small

Acid development too fast

Scald too high

Over salted

Excessive stirring,

combination of speed of

stirring and time

Excess pressure applied

during pressing

Standardize milk fat

Reduce rennet or set time

Cut larger size cubes

Drain at low acidity

Lower scald

Reduce salt

Lower stirring, combination of

stirring speed and time

Apply low pressure during

pressing

3. Overacid cheese Milk acidity too high

Higher moisture in cheese

Salting too late or too little

Too much acid development

before pressing

Too warm during or

immediately after pressing

Reject suspected milk

Scald to higher temperature

Add more salt on time

Control curd temperature

before and during pressing

4. Low acidity cheese Antibiotics in cheese milk

Low moisture content in curd

Reject suspected milk

Adopt low scald temperature

High salt content in curd Use low salt rate

5. Curdy body Low fat

Lacks acid development

Scalding temperature too

high

Standardize milk

Keep required higher acid

Adopt lower scald temperature

6. Greasy Temperature too high during

pressing or ripening

Adopt optimal temperature

during pressing and ripening

7. Mechanical holes Entrapment of air during pre-

pressing or whey level too

low

Cooling the curd too fast

during pre-pressing

Pressure too high or too low

during pressing

Pre-press under whey

Press warm curd

Adopt correct pressing

conditions

8. Bleaching Curd acidity too high Control acid development

9. Mottling Uneven acid formation

Uneven salting

Mixing cheese from different

vats

Control acid development

Ensure even salting of curd

Avoid mixing cheese from

different vats

10. Gassy texture, bitterness,

fruity/yeast flavour

Use of contaminated milk

Low acid and salt content in

curd

Adopt strict hygienic practices,

prevent contamination of milk

Control proper development of

acid and use adequate salt

Defects in Cream cheese product

Cream cheese products with high quality should have a uniform white to light cream color, with

a lightly lactic acid and cultured diacetyl flavor and aroma. The texture of product should be

smooth without lumps, grittiness, or any indication of cracking and wheying-off. The cheese

product should be spreadable at room temperature (68ºF) or when cold (45ºF) if labeled as 'soft',

and the product should be of medium firmness when refrigerated (< 45ºF).

Defects in cream cheese can occur depending on the final pH of the cheese. The texture of the

cheese will be soft, and the cheese will lack flavor, if the pH of the cheese is too high (> 4.7). If

the pH of the cheese is too low (< 4.6), the texture may be too grainy, and the flavor will be too

acidic. In addition, Cream cheese defects include whey separation from the product during

storage and a grainy, sandy, or chalky texture, especially in the lower-fat types.

Defects in Cheddar cheese

Unless the ideal characteristics of a specific cheese variety are known, the defects cannot be

identified. Any deviation from the ideal qualities maybe construed as defect. The ideal

characteristics of Cheddar cheese is described below:

Ideal characteristics of Cheddar cheese

Colour: The color of Cheddar cheese should always be uniform throughout the cheese.

American Cheddar cheese may be uncolored, light to medium colored, or high in color. For

uncolored cheese, the most desired color is a light cream shade; for medium intensity colored

cheese, a deep cream color or a pleasant yellow-orange hue is acceptable. Deep, intense shades

of yellow-reddish hues are generally discriminated against. Even the color should exhibit some

luster. The cheese surface color should be slightly translucent. The ‘translucent’ quality of

Cheddar cheese is closely associated with desirable body and texture.

Flavour and aroma: High-quality Cheddar cheese should possess the characteristic Cheddar

flavor, which is clean, moderately aromatic, nut-like and pleasantly acidic. Usually, aged cheese

has a sharp, aromatic, intense flavor that is entirely lacking in young cheese. The flavor of high

quality Cheddar cheese has been likened to that of freshly roasted peanuts or hazelnuts too.

Body and texture: Cheddar cheese with the most desirable body and texture displays a full, solid,

close-knit plug that possesses smoothness, meatiness, waxiness, and silkiness, and is entirely free

from gas holes or mechanical openings. Cheddar cheese with the above-described quality

attributes lends itself to uniform slicing into thin, intact pieces.

The more prevalent flavor defects that have been associated with retail samples of mild Cheddar

cheese were acid, flat, whey-taint, bitter, utensil, metallic; the less frequently noted defects

included sulfide, fermented, fruity, old milk, oxidized, lipase and high salt.

Of the potential body defects, short, pasty and open were the primary defects identified in the

mild Cheddar cheeses; other less commonly encountered body defects were weak, curdy,

crumbly, mealy, corky and grainy.

Defects in Cheddar cheese

Defects associated with Cheddar cheese

Appearance/Rind

development

Color &

appearance

Aroma Flavour Body-texture

Whey taint Acid cut

(Bleached,

faded)

Rancid/Ammoniated Rancid Cracked

Cracked or

disturbed rind

Mottled Moldy or stale Too acid/sour Crumbly

Too moist/wet Pinking Animal or Barnyard Soapy/chemical Curdy

Uneven Seamy (Uneven

or wavy)

Chemical aroma Bitter/Metallic Gassy

Puffy White specks Unclean Feedy/Fruity Mealy

Surface mold Moldy

appearance

Unpleasantly earthy

aroma

Too salty Waxy

Uneven color Color too

intense

Lacks

flavor/weak

Weak

Moldy/too

earthy

Hard or Corky

Sulfide Slits

Flat Chalky

Too open

Pasty

Short

I. Color and appearance defects in Cheddar cheese

Acid cut: The color of ‘’acid-cut’’ cheese generally appears dull and lifeless, with an opacity that

allows little light to be transmitted through even a thin slice. Quite often, a degree of bleaching

may be noted more or less uniformly throughout the entire cheese.

Generally, the faded color of acid-cut may be associated with high-moisture and high-acid

development in cheese, but it also may occasionally be observed in cheese with a dry body and a

crumbly texture.

Atypical color specks: Atypical color specks take the form of occasional white or black specks,

rust spots, and/or red blotches. White specks may result when color addition to milk is made

prior to incorporation of starter culture due to small clumps of starter not getting colored. Other

sources for specks may include water condensation on dusty pipes dripping into the vat, poor

filtration of milk, or lack of good environmental cleaning and sanitation procedures.

Color too high (Unnatural): This defect is characterized by high color intensity, often by an

orange-yellow hue, especially when pre-cut cheese is warmed to room temperature or higher.

Mottled: The ‘mottled’ color defect appears as rounded, irregularly shaped areas of contrasting

light and dark color, with one shade gradually blending into the other. This defect may result

either from certain physical causes during cheese manufacture or due to atypical microbiological

activity during the curing process. Chief causes are combining of curd from two different lots of

cheese or non-uniform development of acidity within the curd.

Pinking: A ‘pink’ discoloration of cheese occurs when the water-based colorant annatto is

exposed to intense lighting. This defect is most often found in cheese packaged for retail sale and

subsequently subjected to extended exposure to fluorescent lighting in display cases. The

tendency of pinking reaction is more if the cheese has an atypical pH ~ 5.4 (vs. 4.8–5.1 in normal

cheese), or if the packaging used does not present an effective barrier to oxygen.

Seamy (uneven or wavy): ‘Seamy’ is portrayed when the cheese appears interlaced with light-

colored lines around each original piece of curd. Such defect results from physically altered curd

surfaces caused by exuded or crystallized milk fat, uneven salting, or moisture evaporation

especially prior to curd pressing. The wavy color character may be a result of inadequate dilution

of the coagulant prior to addition or excessive agitation or vibration after setting the milk.

White specks: Cheddar cheese that has small ‘white specks’ interspersed throughout its mass

and/or on its surface most commonly occurs in mature cheese; however it may occasionally be a

problem in young- and medium-aged cheeses. These white particles are assumed to be an

admixture of calcium lactate, tyrosine and other components.

II. Flavour defects in Cheddar cheese

Bitter: If volatile, other cheese off-flavors will be detectable by the sense of smell, but bitterness

is noted only by the sense of taste. Bitter taste may occur in mild cheese, but is found more

frequently in aged cheese, as an aftertaste. Certain lactic cultures, coagulating enzymes, and salt

levels have been implicated in the development of this defect. The bitter sensation is somewhat

delayed in terms of its initial perception and tends to persist for some time. Bitterness will

normally intensify with maturation.

Feed: Some feeds, especially high volume roughages, may impart aromatic taints to cheese if fed

to cows within a critical time frame (0.5-3.0 h) prior to milking. This is especially true of

succulent feeds, silage, some commodities, brewery wastes, and some of the hays. A ‘feed’ off-

flavor is characteristic in that it is aromatic, sometimes pleasant (i.e., alfalfa) and can usually be

readily detected by the sense of smell. Feed off-flavors usually disappear rather quickly.

Fermented: The fermented off-flavor in Cheddar cheese is suggestive of acetic acid (vinegar-

like). Some non-starter lactic acid bacteria (NSLAB), such as hetero-fermentative lactobacilli,

may produce significant amounts of acetic acid in cheese during ripening.

Flat/low flavor: Cheese exhibiting this defect is practically devoid of any Cheddar flavor. A flat

flavor is particularly noticeable when the sample is initially tasted. In an aged cheese, flatness

(lacking flavor) represents a more objectionable defect.

Fruity: The ‘fruity’ off-flavor is peculiarly sweet and aromatic; it resembles the odor of

fermenting or overripe fruit, such as an apple or pineapple. The fruity defect intensifies as the

cheese ages and may eventually lead to an unclean or combined fruity and unclean off-flavor.

The fruity defect is attributed to the presence of ethanol-forming microorganisms in the cheese

milk or certain cheese cultures. Esters formed from available ethanol and organic acids are

responsible for the fruity note.

High acid (sour): Lactic acid is a normal component of Cheddar cheese flavor; however, an

excessive acid or sour taste is undesirable. Depending on age, the normal pH range of Cheddar

cheese should be 5.15–5.45. The ‘high acid’ (sour) defect generally results from a too rapid or

excessive lactic acid production in the curd. High acid is by far the most frequently encountered

flavor defect of Cheddar cheese. For some individuals, the high acid off-flavor is sharp and

puckery to the taste.

Oxidized: Occurrence of a metallic (oxidized) off-flavor in Cheddar cheese is quite rare, due to

the reduction–oxidation potential of the cheese interior. This off-flavor is characterized by a flat,

metal-like taste and a lingering pucker sensation. Oxidized (or metallic) cheese milk is the

probable source for this cheese off-flavor.

Rancid (lipase): A ‘rancid’ off-flavor in cheese is characterized by a relatively slow or delayed

reaction time; a prominent odor that may be still noted after sample expectoration; and an

unpleasant, persistent aftertaste. The off-flavor is typically bitter, soapy, and usually somewhat

repulsive. Rancidity is caused by activity of the enzyme lipase on milk fat; this yields volatile,

unpleasantly flavored short-chain free fatty acids (FFA) and their respective salts (or soap).

When the concentrations of FFA from butyric (C4) to lauric (C12) exceed levels desired for a

balanced Cheddar cheese flavor, they impart an off-flavor described as goaty, (cowy is ketone-

like) unclean, bitter, or rancid. Rancid cheese usually results from abusive handling of cheese

milk prior to pasteurization; however, the production of lipases by contaminating bacteria or the

lipase activity inherent to raw milk may also contribute to rancidity, especially in aged cheese.

Sulfide (skunky): The ‘sulfide’ off-flavor of cheese is distinctive; it is similar to the odor of

water with high sulfur content or boiled eggs. Frequently, there is an associated bitter aftertaste,

and/or a burning sensation within the mouth. Numerous sulfur-containing compounds can be

formed during the aging process. In some regions of the world, a moderate sulfide flavor note is

considered essential or highly desirable in sharp or extra-sharp cheese; hence, it is not criticized

when it appears.

Unclean (dirty aftertaste): This defect may suggest to the taster a general lack of cleanliness in

producing the product, given the dirty, lingering, unpleasant aftertaste. This off-flavor persists

long after the sample has been expectorated, and the mouth fails to ‘clean-up.’ Poor-quality or

‘old’ milk used for cheese manufacture is a principal cause of the unclean flavor defect.

Proteolytic and/or lipolytic enzymes, derived from psychrotrophic bacteria or NSLAB, may

cause undesirable chemical reactions to occur within the cheese and result in an unclean off-

flavor.

Whey taint (sour whey): These manifest as various intensities of off-flavors in cheese associated

with retained cheese whey. The slightly dirty sweet/acidic taste and odor is characteristic of

fermented whey. Some cheese authorities’ compare whey taint to the occurrence of a

‘fermented/fruity’ off-flavor, with an ‘unclean’ off-flavor superimposed over it. Some judges

may confuse whey taint and high acid off-flavors; however, only the former defect exhibits the

distinctive aroma of fermented whey.

III. Body-texture defects

Corky (Dry, hard, tough): This defect is generally associated with a low moisture, low fat,

and/or young cheese. The cheese plug taken is stiff or rigid upon bending; it seems to have a

rubber-like consistency. Appearance defects of seamy or acid-cut color may also be exhibited.

Crumbly (friable): A ‘crumbly-bodied’ cheese is one that tends to fall apart when sliced and/or

worked. A plug of such cheese may be extremely friable. This defect sometimes appears to be

associated with curd mealiness (texture defect). A crumbly cheese may sometimes be quite dry.

A crumbly, friable body is more likely to occur in aged cheese (~10 months of aging) than in

young cheese.

Curdy (rubbery): This body defect is quite characteristic of freshly made, ‘green’ (uncured)

cheese. Such cheese usually seems firm, almost hard or rubbery. The plug resists finger pressure;

when it yields to pressure, there is a tendency for the cheese to spring back to its original shape.

This defect is not considered objectionable in mild-aged cheese.

Pasty (smeary, sticky, wet): Cheese showing the ‘pasty’ defect is usually characterized by the

presence of high moisture. The cheese breaks down easily into a pasty, sticky mass that tends to

adhere to the fingertips as the product is manipulated.

Short (flaky): A ‘short’ or ‘flaky’ body is characterized by a lack of meatiness, waxiness, or

overall homogeneity; the consistency of the cheese may appear loose-knit. The plug breaks

easily on bending a short distance and shows a distinct lack of elasticity.

Weak (soft): A weak-bodied cheese is noted by the relatively small amount of finger pressure

necessary to break the structure. Weak-bodied cheese is soft and is closely associated with high

moisture content. When bent between the thumbs and index fingers of opposite hands, weak-

bodied cheese tends to approach touching end to end.

Greasy: A‘greasy’ cheese is one that has free fat on the surface, as well as in and around

openings within the cheese or surfaces of individual curds. The defect is recognized by an almost

oil-like appearance or feel. Greasy-like cheese often exhibits marked seaminess.

Spongy: A spongy-bodied cheese fails to yield a full, continuous plug, due to the presence of

excessive gas or mechanical openings. When a spongy cheese is plugged, it tends to sink

immediately next to the trier. Such cheese is distinctly springy when pressure is applied to the

surface.

Mealy (grainy, gritty): A cheese that shows a lack of uniformity and smoothness, as well as

irregularly shaped, hard particles of cheese, when worked between the thumb and forefingers, is

criticized as being mealy or grainy or gritty, depending on the particle size. A mealy cheese tends

to exhibit dryness and seems to release fat readily. Such cheese exhibits a short body with little

elasticity. Mealiness is most often associated with sharp or aged cheese.

Gassy (pin holes, sweet-curd holes, Swiss holes, shot holes, slits, fish eyes, yeast holes): Gas

holes in cheese vary in size and are fairly uniform in distribution and shape. They are formed

from gas produced by undesirable microorganisms within the cheese. Gas holes are referred to as

‘pin holes’ when they are about the size of a pinhead, symmetrically rounded, evenly distributed,

and/or show a tendency to be concentrated near the center of the cheese. Pin holes may result

from the growth of undesirable bacteria from cheese milk, or a contaminated culture, or a ‘gassy’

culture (formed CO2), that contains Lactococcus diacetylactis or Leuconostoc sp. The gas

formed may also affect the flavor of the cheese i.e. objectionable fruity flavor.

Slits, fish eyes, and yeast holes may be found in cheese made from poor quality milk or starter

culture that has been contaminated with yeast (or coliform bacteria). Cheese that contains

numerous yeast holes usually has a ‘spongy’ body. Yeast holes in cheese may flatten out as the

cheese is cured, forming long narrow slits known as ‘fish eyes.’ Large gas holes are often

associated with a peculiar sweetish, pleasant flavor reminiscent of Swiss cheese; consequently,

they are sometimes referred to as ‘Swiss holes’, ‘sweet holes’, or ‘shot’ holes..

Open (mechanical holes): An ‘open,’ porous, or loose texture is traceable to the physical aspects

of handling and pressing the cheese curd. Mechanical openings are characterized by their

asymmetrical, angular shape and size, and by the dullness of their surface linings. These

irregular-shaped holes may occur due to inadequate matting and pressing of the curd.

Fissures: A fissured texture is characterized by an elongated slit or extended separation of the

curd particles. The curd lacks cohesion, and such defects may be associated with seaminess.

Such affected cheese often lacks the desired meatiness of body.

Defects in Swiss cheese

Examples of Swiss-type cheese include Gruyère, Jarlsberg, Comté, Maasdammer, Appenzeller,

Leerdammer and the most commonly produced cheese with large eyes being the Emmental.

Swiss cheeses are easily identifiable by characteristic round regular eyes that vary in size from 1

to 3 cm in properly produced cheese. French Gruyère contains a small number of eyes, while

Swiss Gruyère is blind. The body of the cheese is hard to semi-hard. Propionibacterium

freudenreichii is the main species used as ripening culture in Swiss-type cheese. The propionic

acid fermentation produces metabolites (propionic acid and acetic acid) that contribute to the

development of characteristic ‘nutty-sweet’ flavours of cheese. The CO2 produced is responsible

for the eye formation.

The size and distribution of eyes are extremely important for the overall quality of Swiss cheese.

The defective cheeses lacked the proper number of eyes (under set) for good quality Swiss

cheese. Splits and cracks, overset and nutshell eyes were other common defects of eye formation

in Swiss cheeses. In one survey, the most common flavor defect in Swiss cheese was utensil off-

flavor.

Split defect: Split and secondary fermentation defects in Swiss-type cheese are manifested as

undesirable slits or cracks. Split defect is associated with an excessive production of gas or an

unsuitable cheese body that cannot accommodate gas produced, or a combination of both factors.

Secondary fermentation is the apparent production of gas after the desired propionic

fermentation of the warm room has taken place. Such defect has a negative impact on the

openness and elasticity of cheese.

Secondary fermentation is linked with split defect as an apparent resumption of gas production

which occurs during the cold room ripening (after the desired propionic acid fermentation of the

warm room ripening), causing splitting and variation in eye size of the cheese. Such secondary

fermentation is affected by the aspartase activity of propionic acid bacteria, the presence of

facultatively hetero-fermentative lactobacilli and the use of L. helveticus as a component of the

starter.

Methods to reduce the prevalence of the split defect and secondary fermentation include addition

of water to improve elastic properties by the removal of unfermented carbohydrate and the use of

hetero-fermentative lactobacilli to control propionic acid bacteria activity to prevent the

production of excessive gas.

Defects in Mozzarella cheese

Defects associated with Mozzarella cheese include a rubbery, tough texture, lack of flavor,

paleness or green tint, inability to melt and poor stretchability.

Pink discoloration: This type of discoloration of cheese was earlier associated with Swiss

cheese, Italian cheeses other than Mozzarella (Romano, Parmesan, Provolone, Asiago, Fontina)

and annatto colored cheeses. The discoloration of Italian cheeses was associated with the non-

dialyzable fat-free fraction. Some shredded samples of Mozzarella cheese that the wholesalers

had kept for 6 months started turning pink in color. Upon opening the bag (in presence of

oxygen), the cheese turned back to the normal white colour.

Pink discoloration 1-2 cm under the surface of Swiss cheese was influenced by the strain of

Propionibacterium used; more so with P. shermanii rather than P. arabinosum. The discoloration

occurred during final stages of cooling while being cured at 3-7oC. In both cases the color faded

in few hours after the cheese was cut and packaged. Such pink zone was related to the oxygen

diffusion into the cheese.

Aqueous based annatto color (i.e. norbixin) in cheese (i.e. processed cheese) often caused pink

discoloration defect. Cheeses made with sodium citrate showed more color change than did

disodium phosphate. Use of aged and acid cheese to produce processed cheese contributed to

pink discoloration. Pinking occurred when the pH of cheese was reduced from 5.4 to 4.8. The

cheese product was more susceptible to pink or brown discoloration when produced with higher

cooking temperature. The frequency of discoloration was low if the cheese was cooled

immediately after production. High intensity lighting in grocery stores catalyzed the pinking

effect of annatto colored cheeses.

Soft, wet/Slimy surface: Brine-salted Mozzarella cheese sometimes develops a soft, wet surface

during storage. The temperature differential, which develops during exposure of the warm cheese

to cold brine and then dissipates slowly during post-brine cooling, is implicated in the

development of ‘soft surface’ defect in Mozzarella cheese

Too chewy for pizza pies: Consumers do not prefer to consume pizza topped with Low-moisture

part skim Mozzarella cheese (LMPS) cheese that is too chewy. The low-fat pizza cheeses (< 18

% fat) have dense protein matrix which leads to too chewy mouth feel. Controlling moisture and

fat content in such cheeses can avoid such defect.

Poor shredability: Since Pizza cheese (LMPS) is used as a pizza topping, shredability of cheese

is of great significance. The cheese should be amenable to shredding into thin, long shreds which

do not mat post-shredding. Mozzarella cheese, with higher fat (> 25%) and lower protein content

(< 20%), produced the most fines during shredding of cheese. Tack energy increased with

increasing fat content in cheese. The rheological properties and tack energy appeared to be the

key factors involved in shredding defects.

Some probable defects in hard cheeses

Late blowing in cheese

Butyric acid fermentation, the late-blowing defect in cheese, caused by the outgrowth of

clostridial spores present in raw milk and most commonly originating from silage, can create

considerable loss of product, especially in the production of semi-hard cheeses like Gouda

cheese, but also in Grana and Gruyere cheeses. The presence of C. tyrobutyricum leads to

occurrence of butyric acid fermentation in cheese. Hence, for the production of semi-hard

cheeses like Gouda cheese, it is important to limit the number of spores of bacteria capable of

causing late blowing in the cheese milk to less than 1 spore per 10 ml.

If extensive proteolysis occurs during aging of ripened cheeses, the release of amino acids and an

increase in pH favors the growth of clostridia, especially Clostridium tyrobutyricum, and the

production of gas and butyric acid. Spores are concentrated in cheese curd, so as few as 1 spore

per ml of milk can cause gassiness in some cheeses. Spore numbers of > 25/ml were required to

produce this defect in large wheels of rindless Swiss cheese. Cheeses most often affected, e.g.,

Swiss, Emmental, Gouda and Edam have a relatively high pH and moisture content, and low salt

content.

Gassiness in cheese

Occasionally, gassy defects in process cheeses are caused by Clostridium butyricum or C.

sporogenes. These spores are not completely inactivated by normal cooking treatment in process

cheese making. Therefore, they may germinate and produce gas unless their numbers are low,

the pH does not exceed 5.8, the salt concentration is minimum 6% of the serum, and the cheese

is held at 20◦C.

Defects in Processed cheese and cheese spreads

I. Appearance defects

Pink discolouration: Pink discoloration has sometimes been noted in process cheeses that were

either artificially colored with annatto or used a natural cheese, which had annatto color added to

it. Use of alkaline extracts of annatto in process cheese showed a higher propensity to cause such

defect. An increase in the amount of colored natural cheese in the blend led to an increase in the

pink discoloration of process cheese. When the ratio of aged cheese (uncolored) was increased in

the natural cheese blend (uncolored) during process cheese manufacture with added annatto

colorant, there was an increase in pink discoloration.

Browning: Various factors influence browning through Maillard reaction in process cheese.

Browning is initiated when ingredients with high lactose content are used during process cheese

manufacture. Additionally, high process cheese final pH (> 5.9) and high storage temperatures

(~ 37◦C) have been found to accelerate browning in process cheese. A high correlation was

found between salt-to-moisture ratio and levels of residual galactose and lactose of Cheddar

cheese on the browning of process cheese. Therefore, careful selection of ingredients and

optimum final pH during process cheese manufacture, along with desirable post manufacture

storage conditions can help in preventing browning defect in process cheese.

Crystal development: Different crystals have been sometimes noted in natural cheeses such as

tyrosine, calcium lactate, various salts of calcium phosphate and calcium citrate. The types of

crystals identified in process cheese ranged from salts of calcium tartrate (less incidence these

days), calcium citrate, tertiary complexes of Na- and Ca-citrates, various salts of Na- and Ca-

phosphates, and, sometimes, calcium salts of free fatty acids. Other types of crystals that can

occur in process cheese are lactose crystals. Lactose crystallization in process cheese can be

avoided by maintaining the level of lactose below its maximum solubility level in the water

phase of cheese. However, major sources of crystal development in process cheese are due to the

use of emulsifying salts such as various salts of phosphates and citrates. The process cheese

industry commonly rely on an 85:15 rule of thumb ratio (citrate:phosphate), when using blend of

citrates and orthophosphates. Additionally, proper storage condition of cheese is important to

prevent crystal development. In contrast, tetrasodium pyrophosphate (TSPP) crystals form when

TSPP is in contact with free water. This is an exothermic reaction that can fuse TSPP and water.

These small inclusions provide a seed for TSPP to grow into large crystals in or on the surface of

the cheese within 1-2 months of cheese making. To avoid this problem, adopt dry blending TSPP

with sodium chloride and not adding free water at the same time when incorporating TSPP.

Manufacturing equipment such as casting lines and slice cooling belts have also been associated

with promoting crystal development in process cheese, as they can act by providing nucleation

sites for crystallization when not cleaned properly.

If the aged cheese already has some tyrosine crystals, they will not dissolve upon cooking. This

may be tackled by either filtering out the crystals or limiting such aged cheese or both.

II. Functional defects

These defects can range from very high to very low meltability, very high to very low firmness,

presence of stickiness, etc. These properties can be adjusted to the desired levels by appropriate

control of various formulation and processing parameters in process cheese manufacture.

III. Body-texture defects

Process cheese may also be prone to defects in body and texture such as brittle, crumbly, grainy

texture, and even oil separation.

Brittle, crumbly and grainy texture: This type of defect arises when the final pH of the process

cheese is too low (< 5.4), desired pH being 5.6-5.7. This is due to its closeness to isoelectric

point which gives decreased net negative charge on the protein.

Oil separation: This defect arises due to improper emulsion formation of the cooked process

cheese. Improper emulsification of the process cheese can occur due to (i) too low or too high

level of emulsifying salts, (ii) low final pH of process cheese, (iii) low level of intact casein in

the process cheese owing to use of highly aged natural cheese in the cheese blend, or (iv)

inadequate or extensive processing temperature and/or time adopted during process cheese

manufacture.

Microbial spoilage of cheeses

Factors that determine the rates of spoilage of cheeses are water activity, pH, salt to moisture

ratio (SM), temperature, characteristics of the lactic starter culture, types and viability of

contaminating microorganisms, and characteristics and quantities of residual enzymes. Soft or

unripened cheeses, which generally have the highest pH values, along with the lowest SM ratios,

spoil most quickly. In contrast, aged, ripened cheeses retain their desirable eating qualities for

long periods because of their comparatively low pH, low water activity, and low redox potential.

For fresh, raw milk pasta filata cheeses, low initial salt and higher brining temperature (18◦C)

allowed for greater growth of coliforms, which caused gas formation in cheese. Factors affecting

the growth of Enterobacter agglomerans and Pseudomonas spp. in cottage cheese, were higher

pH and storage temperature of cheese. Some of the spoilage microorganisms were able to grow

at relatively low pH values (4.6–4.7), when incubated at 7◦C and were able to grow at pH 3.6 at

20◦C. Rate of salt penetration into brined cheeses, types of starter cultures used, initial load of

spores in the milk used for production, pH of cheese, and ripening temperature affect the rate of

butyric acid fermentation and gas production by C. tyrobutyricum. Fungal growth in packaged

cheeses was found to be most affected by the concentration of CO2 in the package and the water

activity of the cheese.

Cheddar cheese exhibiting yeast spoilage had a high moisture level (39.0%) and a low salt in

moisture-phase (3.95%). The properties of yeasts that affected the spoilage rate of Camembert

and blue-veined cheeses were the abilities to ferment/assimilate lactose, produce extracellular

lipolytic and proteolytic enzymes, utilize lactic and citric acid, and growth at 10◦C.

Molds can grow well on the surfaces of cheeses when oxygen is present; low pH being selective

for them. In packaged cheeses, mold growth is limited by oxygen availability, but some molds

can grow under low oxygen level. Molds commonly found growing in vacuum-packaged cheeses

include Penicillium spp. and Cladosporium species. A serious problem with mold spoilage of

sorbate containing cheeses is the degradation of sorbic acid and K-sorbate to trans-1,3-

pentadiene, causing an off-odor (kerosene-like). Cheese-spoilage isolates of Penicillium spp.

were resistant to up to 7,100 ppm of K-sorbate. Sorbate-resistant strains of Paecilomyces variotii

and D. hansenii (a yeast) have been isolated from Crescenza and Provolone cheeses, that

produced trans-1,3-pentadiene, causing off-flavors in such products.

Cream cheeses are susceptible to spoilage by heat-resistant molds such as Byssochlamys nivea.

Byssochlamys nivea is capable of growing in reduced oxygen atmospheres, including

atmospheres containing 20 to 60% CO2, with less than 0.5% oxygen. Once this mold is present

in the milk supply, it can be difficult to eliminate during normal processing of Cream cheese.

Washed curd types of cheeses are susceptible to growth of coliforms, hence care must be taken

to monitor the quality of water used. A high incidence of contamination of brine-salted cheeses

by yeasts results from their presence in brines. Many mold species are adapted to the cheese-

making environment and can be difficult to eradicate from a production facility. Fungi causing a

‘thread mold’ defect in Cheddar cheeses were found in the cheese factory environment, on

cheese-making equipment, in air, and in curd and whey. Penicillium commune persisted in the

cheese coating and unpacking areas over a prolonged (7 year) period.