Dairy Products
Module- 30
Lec- 30
Dr. Shishir Sinha
Dept. of Chemical Engineering
IIT Roorkee
Dairy: Cheese
• The processing of milk into cheese is a relatively simple task that involves basic aspects
of food chemistry.
• In the conversion of milk into cheese, we see the importance of
– water activity,
– oxidation/reduction
– potential, and
– pH;
– lipid,
– carbohydrate, and
– protein chemistry;
– mineral-protein interactions.
CATEGORIES OF CHEESE
• Different ways to categorize cheese might include
– coagulation type,
– ripening method, and
– texture
Coagulation Type
Acid only: that utilizes only acids
– Cottage cheese,
– cream cheese
• These cheeses typically have higher moisture (50–80%) and contain significant quantities
of residual lactose.
• Heat and acid: that have a heat step included in the precipitation of the casein protein of
the milk.
– Ricotta and
– quesoblanco
• Moisture is (50–70%).
• no microbial growth
• Significant amount of lactose.
• Acid and enzymes:Acid is produced by added or naturally occurring lactic acid bacteria
and a coagulating enzyme is added to form the curd.
– Cheddar,
– Swiss style
– brick,
Ripening Method
• Fresh unripened cheeses.
• Soft, surface mold ripened cheeses.
• Internally mold ripened
• Surface bacteria ripened.
• Internally bacteria ripened stirred curd
• Internally ripened curd.
• Internally ripened secondary culture.
Texture
• Very hard
• Hard.
• Semisoft
• Soft.
RAW MATERIALS PREPARATION
PRETREATMENT OF MILK
• Milk for cheese manufacture may be raw, heat treated, or pasteurized.
• Heat treatment is considered any heating that would not be considered pasteurization.
• heat treatment and pasteurization kill many of the microorganisms in raw milk, variation
in cheese flavor and yield is reduced.
CURD FORMATION
• The enzymatic process is generally in two stages:
– enzymatic action and
– the resulting aggregation of micelles.
• The addition of a milk-clotting enzyme causes the slightly acidic milk to coagulate into a
gel.
• The moisture content is about the same as that of the original milk, 87%.
CUTTING and SALTING
• handling of the cut curd is a major determinant of the final cheese type.
• Once the milk has been coagulated, the gel is cut with knives into small pieces.
• Cutting aids in the loss of moisture and causes some loss of fat from the curd.
• The whey portion of the milk contains a dilute solution of serum proteins, lactose, and
minerals.
• Separation of the whey from the curd may be accomplished by following methods:
– Dipping,
– straining,
– draining,
salting
• Salting is useful for several reasons, including taste and texture, preservation by lowering
water activity and inhibiting of bacterial growth, and control of the final pH of the
cheese.
• In Cheddar-type cheeses, after the mat has formed and been cut into blocks, the blocks
are mechanically cut into small rectangles (fingers) prior to salting.
• In other types of cheeses, the salting is done using a brine solution.
CHEMISTRY OF CHEESERIPENING/AGING
• Aging :
relatively flavorless curd is transformed into a product with hundreds of compounds that
contribute to the overall flavor of the final cheese.
• These transformations of the proteins, carbohydrates, lactic acid, and lipids are caused by
several things, including
– enzymes present in the milk,
– added enzymes,
– enzymes released from various microorganisms,
– metabolism of added and adventitious microorganisms, and
– spontaneous reactions caused by the low oxidation/reduction (Eh) potential of the
final block of cheese.
• The ripening process will be described in terms of changes to each of the major
components of the milk and the causes of those changes.
FINISHED PRODUCT
• In some cases, this has resulted in a very uniform product without much of the traditional
flavor associated with the cheese.
• Some current automated methods of Cheddar cheese manufacture have produced a very
bland product without much character.
APPLICATION OF PROCESSING
PRINCIPLES
Processing stage Processing Principle(s)
Pretreatment of milk • Heat treatment or pasteurization
• Homogenization
Unripened acid-coagulated milk Acid concentration of proteins
Curd formation • Concentration/precipitation of protein
• Syneresis or drying of curd
• Water activity reduction
• pH reduction
Chemistry of cheese ripening/aging • Enzymatic modification of components
• Competitive microflora
Dairy: Ice Cream
• Ice cream is a frozen food made from milk fat, milk solids-not-fat, sweeteners, and
flavorings; a variety of fruits, nuts, and other items also may be added.
RAW MATERIALS PREPARATION
• Typical ingredients received into an ice cream making operation would include
– milk fat sources,
– milk solids sources,
– sweetteners,
– stabillizers and
– emulssifiers,
– colorss,
– flavors, and
– particu
ulate materiaals—nuts, frruits, and canndy pieces
PROCESSING FLO
OW DIAGR
RAM
process stage 1
Process stage 2
Dairy: Milk
M Powderrs
RAW MATERIALS
M S PREPARA
ATION
• Raw
R milk preeparation con
nsists of the following opperations
– receiv
ving,
– selection,
– clarifiication,
– coolin
ng, and
– storag
ge.
References
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