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 • • • • • • • • • 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 • • • • • • • 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 • • • • • • • • 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 • • • • • 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 – – – – – – 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 . 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.
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