Cheddar Cheese Defects
Mark E. Johnson
Wisconsin Center for Dairy Research
University of Wisconsin, Madison, WI
Milk Quality
Starter
Secondary
Manufacturing Process
[Ecology]
Non-Starter
Adjunct
Cheese
Chemistry
Strain
Storage
Shelf-Life
Cheese Flavor
Functional Properties
Cheese Defects
• Most cheese defects are related to five areas:
1. Improper moisture content
a) In relation to fat and casein level in
cheese or aging requirements/storage
conditions
b) Usually related too much fat and too
much moisture or too little casein (too pasty
or weak) = excessive proteolysis
Cheese Defects (continued)
2. Improper rate and extent of acid
development
In relation to protein content of milk and
desired physical attributes of cheese
(high pH = tough or low pH = short and
acid)
3. Poor quality ingredients (flavor and
body)
4. Microbial contamination
5. Retail abuse
Dissecting a Cheese : Record Keeping
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Detail all observations
Odor, color, free fat on milk surface
Starter growth conditions
Keep records of manufacturing protocol
pH/Titratable acidity
Temperature-Times
Curd firmness at cut, drain, hoop
Ripening conditions
Freeze small sample of vat milk
As Milk Composition Changes Cheese
Composition Changes
• In stressed animals (hot months)
– Less casein
– Fat drops but not at a lower rate than
casein
– Cheese will have a higher fat content and
a higher moisture content
• Cheese will be softer and have a
shorter shelf-life
Standardize Milk Composition to
Control Cheese Composition
• Maximize cheese yield productivity
– More cheese per vat
– More cheese per 100 weight of milk
– More cheese per worker hour
• Decrease variability in cheese
composition and quality
Fat on Dry Basis (FDB)
FDB of cheese is determined by calculating
the ratio of casein to fat in milk (C/F)
FDB =
% fat in cheese
% total solids in cheese
C/F = % casein in milk
% fat in milk
Casein to Fat and
Protein to Fat Ratios
Milk composition: 3.6% fat, 3.2% protein
Calculating casein from protein
If true protein is 3.2% then :
casein = 3.2 x 0.82 = 2.64%
C/F = 2.64% casein = 0.73
3.6% fat
P/F = 3.2% protein = 0.88
3.6% fat
C/F and FDB
MILK
C/F = 0.70
C/F = 0.65
CHEESE
FDB = 0.52
FDB = 0.54
Casein to Fat = C/F
Fat on a Dry Basis = FDB
High FDB vs Low FDB
• High FDB (>55 %) need to decrease
moisture of cheese (< 37.5 %) or body will
be too soft
– Remove cream or add skim
• Low FDB (<52 %) need to increase
moisture of cheese (>37.5 %) or body may
be too rubbery/firm
– Add cream
High Moisture Results In:
– Increased retention of lactose which in turn
leads to low cheese pH
– Faster increase in microbial numbers
• Potential for abnormal fermentations
– Slow starter die-off: more bitterness
– Accelerated enzymatic changes
• Proteolysis : softer, pasty body
• Shorter shelf-life
Low Moisture Results In:
• Decreased rennet activity: less proteolysis
• Decreased rate of flavor development
• Textural changes don’t occur as rapidly,
cheese remains firm or corky.
Steps used in Cheese Making to Decrease
Moisture
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Make smaller curd particles during cutting
Cut the gel softer and at a higher pH
Cook at higher temperature
Develop more acid during cooking
More “dry-stirring” of curd after whey
drainage (stirred curd)
Stir-out longer after salting
Apply slow but more pressure
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Additional Steps Used in Cheese Making to
Increase Moisture
Add a little salt to whey before draining
If milled curd: pile higher/increase depth of
curd
Rinse curd in cold water
Develop acid in form (hoop) rather than in
vat
Less stir-out before drain
No Pressure
Add less salt
Less brine time
Excessive Acidity/Low pH (<5.0)
Characteristics of Cheese:
– Short/brittle body in
dry hard cheese
– Pasty body in soft cheeses
– Grainy mouthfeel, acid and bitter taste
– Cheese loses serum
• Cheese more prone to crystals on surface
• Cheese more prone to growth of
microorganisms at the surface : Rind rot if
packaged
Calcium lactate crystals
Calcium lactate crystals
Cheddar cheese pH 4.75
Why Cheeses are Acid
– Manufacturing schedule
–High moisture cheese
–Low pH at cut
»Depends on protein (casein)
content
–Low pH at milling/salting
–Aggressive culture (Fast acid
producing cultures) / with high salt
tolerance
–Low salt in cheese
The Race:
• The starter will continue to produce acid as
long as are nutrients to allow it to grow and
as long as there is sugar remaining
– Fast cultures create peptides via strong
proteolytic system that allow fats growth
– Slow culture are not very good at doing that
• Starters grow as long as the temperature is
warm enough and salt content is low
enough to allow it to grow
The Race:
• The cheese pH will drop below pH 5.0 (an
acid cheese) and typically as low as pH 4.85
with no salt added.
• If the rate of acidification is so fast by the
time salt penetrates the curd the starter may
have lowered the pH too low (acid cheese).
• Low pH at milling or salt addition means
that the penetration of salt into the curd may
not be fast enough to stop the culture before
pH of 5.0 or less is reached.
The Race:
• The pH of any cheese is regulated by
– Sugar content of milk and cheese
• Added milk solids from heat condensed or
RO membrane separated milks will increase
sugar in the serum phase of milk
– Buffering capacity of the casein (bound
calcium phosphate)
• Ability to keep the pH from dropping too
low
• Excessive low pH at drain can remove
some buffering capacity
pH Profile
pH at
rennet
pH at
salt
Final
pH
6.5
6.3
6.1
5.35
5.35
5.35
5.05
4.95
4.90
Non-standardized milks:
Cheese moisture at 37 %
What can be done?
• Remove lactose
– Remove whey and add back water
• 10% in traditional Swiss, 25 % in Gouda
– Rinse curd-or soak curd
• Contact time dependent
– If lactose removal is excessive it could lead to
lack of traditional flavor development in aged
Cheddar cheeses
What can be done?
• Slow down acid development
• Use less starter
• Reduce ripening time
• Add rennet early
– Cooling and salting are the natural means to
stop fermentation
• Problem with fast salt insensitive cultures
– Salt at higher pH
– Change to slower acid producers
High pH (>pH 5.3)
Slow salt sensitive culture or dead vat due
to phage
• Corky body (too firm)
• Curdy body (feels like individual curds in mouth)
– Poor machinability
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Potential for pathogen growth
Potential for coliforms
Poor melt
If added too much salt : also crumbly
Residual sugar may be high (browning-gassy)
What can be done?
• Increase acid development
• Use more starter
• Increase ripening time
– Cooling and salting are the natural means to
stop fermentation so
• Keep curd warm (~ 34 C)
• Salt at lower pH
– Change to faster acid producers
Bitterness : Factors That Contribute
• Starter
– Low salt in cheese
– Fast cultures (often associated with excessive
acid)
• Salt/mill earlier
– Coagulant (type and amount) + starter
What to do: Most effective :
Change starter culture
Increase salt addition (will lower moisture
Add debittering adjunct
Proteolysis: Break down of casein
Disconnected + large peptides
Connected aggregates (Farrell)
Proteinase
(coagulant)
Bacterial
proteinases
Aldehydes,
ketones, etc
NH4
CO2
Bacterial
peptidases
Amino acids
H
H2N - C - C =O
OR
(amino
peptidases)
Small peptides
(bitter)
30
Other flavors: ~lingering unclean notes
Microbiological (many Lactobacilli)
-barny -catty -cowy -chemical (phenols, cresols)
-fruity (fatty acids+ alcohol)
Other off-flavors
-feed (oxidized, fish-like notes from soy bean meal)
-oxidized (due to light induced or sanitizer oxidation of fat)
-rancidity (milk from mastitic animals, excessive agitation
of raw milk
Decomposition Steps of Amino Acids during Ripening of Cheese
Paracasein
D. Hemme et al., Science
des Aliments 2(1982)113
Proteolysis
Amino acids
Oxidative
deamination
Transamination
NH3
Decarboxylation
Degradation
CO2
Level 1
α-keto acids
amino acids
amines
Oxidative
deamination
CO2
CH3SH
phenols
indol
Level 2
NH3
aldehydes
Reduction
Oxidation
Level 3
alcohols
acids
sulfur
compounds
32
Defects in Cheddar-types
• Loose and open textures (mechanical
openings)
• Causes
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Development of too little acid
Pressing too fast
Lack of pressing
Cold curd
High salt
Curd too dry
Gassy Defects
– Presence of high levels of sufficient numbers of
gas-producing bacteria
– Coliforms (rare in pasteurized milk cheeses)
– Leuconostoc (uncommon) Lc. Lactis, Lc
mesenteroides
– Heterofermentative lactobacilli (very
common)
• Lactobacillus fermentum, Lb, buchneri, Lb.
brevis
– Facultative lactobacillus (becoming common)
• Lactobacillus curvatus
Substrates Utilized
• Lactose (incomplete fermentation by
starter)
• Galactose (released from lactose by
thermophilic bacteria)
• Flavor enhancing adjunct Lactobacillus
helveticus
– Streptococcus thermophilus
• Starter
• Contaminant and survives
pasteurization and forms biofilms in
regenerative section
Lactobacillus curvatus fermenting residual galactose
Residual galactose from Streptococcus thermophilus
(starter or from biofilm contaminant)
Puffy package of Cheddar cheese
Cheese held at 13 C
Gassy cheese
Huffed Package
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Cheese ripened at 13 C. No heterofermentative bacteria
found, no off-flavor.
Why Talk About Biofilms?
We are searching for the source of
bacteria that cause issues during
cheese making or in the finished
product.
Biofilm
Biofilm
Thinking about Biofilms
Why do they happen?
Biofilms are the natural state of microorganisms
in the environment
Biofilms are a means of protection and
adaptation
Microorganisms forming a biofilm may already
existed in a previous biofilm
Microorganisms in Biofilms
Attachment sites of biofilms on
equipment are probably where
they can “hide” : areas of
restricted flow
Gaskets/ straight angles/cracks
Where moisture/milk can
collect after drainage
Pipe surface
Gasket
Pipe surface
Biofilm develops
Surface tension allows for
milk to collect at this site
and not drain
How often are gaskets changed?
Original Source of Bacteria in Milk
Number 1 original source of our problem
bacteria are soils/vegetative matter
High numbers of bacteria in milk correlate to
high amount of sediment in milk, which relates
to teat cleanliness at milking.
Teats get contaminated with:
Bedding material (bio-solids) and manure flushing
(Doug Reinemann-UW Biological Systems
Engineering)
Improperly fermented or stored silage
(generally through feces)
Mud
Feces
Improper pre-milking teat treatment
with inadequate cleaning of teats and
legs being the most problematic
As a result of contact with contaminated
teats, equipment and milk get contaminated
Cracked rubber seals/gaskets (biofilms)
Significant buildup of bacteria in milk residue (biofilm)
This indicates a PERSISTENT CLEANING FAILURE
Pam Ruegg UW Dairy Science Extension Milk Quality
Specialist: “ wash failures” improper water
temperature (should be >70ºC), inadequate detergent
strength, and low sanitizer strength.
Guterbok, W.M., and P.E. Blackmer, 1984. Veterinary
Interpretation of Bulk Tank Milk.
Veterinary Clinics of North America: Large Animal Practice,
Vol. 6, No. 2, July 1984. pp. 257-268
How bacteria are counted is
important
Laboratory Pasteurization
Count
Simulates LTST pasteurization 63
C/30 min
Standard Methods Agar at 32 Cº
for two days
Pick up thermoduric mesophiles
including activated spores some
lactobacilli, and micrococci and
others.
How bacteria are counted is
important
Laboratory Pasteurization Count
Probably will miss the
thermoduric thermophiles:
heterofermentative
lactobacilli and
Streptococcus thermophilus
Suggest using ST agar (at 42ºC/two
days) for streps and Rogosa SL agar
(at 32ºC and 37ºC for two days) for
lactobacilli
Biofilm Location in Cheese
Plant
Regenerative section of pasteurizer and piping
from pasteurizer
Milk is warm : allows rapid growth of bacteria
Any location where flow is inconsistent
• Hidden spots: gaskets, dead-ends, valves
Lab Pasteurization Count
Compare LPC to actual number in plant
pasteurization numbers
If numbers of selected bacteria are higher
in the in-plant pasteurizer milk than the
LPC
Indicates biofilm exists in pasteurizer .
Red Flags for Potential
Biofilm
 High numbers of selected bacteria in pasteurized
milk
If numbers in raw milk or LPC do not increase
substantially during the day but …….
Selected bacteria increase in cheese from early
vats to later vats
Counts of selected bacteria increase substantially
over the day
Numbers of selected bacteria exceed certain
values
Streptococcus >100 cfu/ml milk
Lactobacillus > 10 cfu/ml (generally is
<1/ml)
No. of Bacteria (Log)/ml of milk
Progression of a Biofilm: Samples taken from freshly
pasteurized milk
6
5
4
3
2
1
0
0
2
4
6
8
Time (h)
Rapid increase indicates Biofilm already existed
Be Worried -Be Very Worried
about an Established Biofilm
It may take several days or
weeks to establish a biofilm on
clean equipment
But once formed it will be very
hard to completely remove
Suggests vigilance in cleaning
and sanitation before you see
the numbers of bacteria in milk
that would suggest a biofilm has
formed
Case History: Biofilm
Severe early (2 weeks) gassy cheese defect in
Cheddar
Isolated Lactobacillus fermentum from raw milk,
pasteurized milk and cheese
High counts of Lb. fermentum in incoming milk
Pasteurized milk had lactobacillus (Rogosa SL
agar-37ºC) >1000 cfu/ml milk
How do we get rid of the undesirable
microorganisms?
• Keep all microorganisms out of the milk and
prevent growth of those that are present
– Overall cleanliness
– Sanitation (time/temperature of contact)
– Cool rapidly < 4 C and keep cold
• Remove/kill those that are in milk and prevent
contamination
– Pasteurization
– Thermization
– Physical removal (membrane or separator)
• Prevent contamination after cheese is made
– Overall cleanliness
– Sanitation
– Air-handling
• Create conditions in the product that will either kill those
that are in the finished product or prevent them from
growing
– Low pH (< pH 5.4)
– Rapidly cool product less than 4 C
– Low Storage Temperature = 4 C or less (especially
retail)
Watering Off
• Most (90 %) moisture in cheese is mechanically
trapped within the protein network of the cheese.
• However certain conditions lead to moisture
release:
– pH (too low or too high)
– Salt (too high)
– Temperature (coupled with low pH or high
salt)
– Proteolysis (in a high salt, or low pH cheese)
Van Vliet and Walstra (1994)
Calcium lactate crystals
occur at buckling sites in
package
Calcium Lactate Crystals at plastic
wrap buckling sites, plastic wrap remove
Buckling Package
Material
Serum collects at interface
Calcium lactate crystals form
at interface and spread
Mold, yeast, bacteria
growth (rind rot)
Air
Cheese Surface
Yeast and Mold
• Causes
– High moisture in environment/free moisture on
cheese surface
– Loose packaging
– Environmental contamination (air, water, dust)
• Prevention
– Proper packaging
– Dry environment
– Air filtration
– Sanitation/fogging
– Use of antimycotic
Additional Contributors to Cheese Defects
• Light exposure
– oxidized flavors, color bleaching
• Exposure to chlorine/bromine
– oxidized flavor
• Temperature abuse
– Moisture migration- watering off
• Excessive aging (proteolysis = excessive softening)
• Milk quality
– Mastitis: lipase (leads to rancidity)
Color fade in grass-based
cheeses
• Carotenoids are subject to
light oxidation
• Packaging should have
low Oxygen Transfer Rate
• Light intensity should be
less than 250 footcandles
• Good inventory control to
minimize light exposure
(Wendorff, 2007)
Interior 1 cm from surface
Label
Original surface
Light Induced Pinking and Bleaching : Cheddar Cheese
Light intensity is one key to
controlling pinking
160-200 footcandles
640 footcandles
Factors affecting pink
discoloration
• Lighting type and intensity
– Cool white is worse than soft white
– Light intensities above 300 foot candles will cause
pinking within 48 hr.
• Storage time and temperature (8˚C>2˚C)
• Cheese composition
– pH 5.4, bleaching pH 4.8-5.1, intense pink
• Source and age of colorant (pinker with age)
• Packaging systems and films
– Lower oxygen transmission rate (OTR)s, less pinking
and oxidized flavor
• UV blocking sleeves (Not effective)
(Wendorff, 2006)
The other key to eliminating
pinking is packaging
Full exposure
Limited exposure
Summary: Prevention of Defects
• Sanitation on the farm and factory
– Keep problem microbiota out; prevent biofilms
• GMP in the factory: Employee training
• Cheese starters: watch the speed
• Milk composition:
– Watch for changes in casein and fat levels
– Do not use mastitic milk
• Cheese Composition
– Proper moisture (fat), salt and pH in cheese is
essential for managing cheese quality through-out
ripening
and retail.