processing of milk

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• I.K GUJRAL PUNJAB TECHNICAL UNIVERSITY
  KAPURTHALA, PUNJAB
• DEPARTMENT OF FOOD SCIENCE AND TECHNLOGY
• Topic
• Various stages of processing, clarification, and
  storage of milk
• Submitted by Rahul
  Submitted to Dr. Amandeep Kaur
• Roll no. 2124667
  (Assistant
  professor)

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What is milk and fluid milk.

• Milk the lacteal secretion, practically free
  from colostrum, obtained from the complete
  milking of one or more healthy milch animals.
• Fluid milk Fluid milk is an industry term
  for milk processed for beverage use.

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Receiving of milk

• Milk may be delivered to the milk plant in cans
  or tankers (Road/Rail).
• The milk in these containers has to be graded,
  emptied, measured by weight or volume, sampled
  and bulked to provide continuity of supply to the
  pasteurizing equipment.
• Milk reception should be complete within
  3-4hours, especially in tropical countries.

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Various steps

• UNLOADING Milk cans are unloaded manually from
  truck. If the level of truck is in line with the
  platform, the unload requires least effort. If
  the milk tanker is being used, it is first
  properly positioned so that connections can be
  made conveniently
• GRADING It refers to the classification of milk
  on the basis of quality for the price fixing
  purposes. Milk grader is used for proper
  selection of milk.
• Principle of grading is based on organoleptic
  test (smell, taste, appearance acidity,
  sediment etc. which are included in Platform test.

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 PLATFORM TEST

• It refers to the test which are performed to
  check the quality of incoming milk on the
  receiving platform so as to make quick decision
  regrading its acceptance or rejection. Some of
  the platform tests are
• Smell (Odor) This furnishes an excellent
  indication of organoleptic quality of milk. An
  experienced milk grader with trained nose
  usually relies to great extent in the
  acceptance/rejection of the intake milk on odor
  test alone.
• Appearance Milk should be normal in color
  (Yellowish Creamy Cow Milk Creamy White
  Buffalo Milk) free from churned fat globule
  free from extraneous matter.
• Temperature By touching the sides of can milk
  grader checks the temperature. A temperature 5C
  or below is satisfactory.

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• Sediment shows visible foreign matter.
• Acidity shows natural and developed acidity.
• Normal Acidity range 6.5-7.0
• SNF Gives specific gravity of milk.
• Check adulteration of milk with water.
• Range 8.5-9.0
• Alcohol Stability against heat.
• And many more.

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3. Sampling

•  It is very important in any quality testing of
  food material either milk or any other.
• PREREQUISTS OF SAMPLING OF MILK
• Thorough mixing of the milk by using
  stirrer/agitator in the can/tanker.
• Representative samples can also be taken during
  dumping of milk can into weigh tank, whereby milk
  gets mixed so thoroughly.
• Collected composite samples were placed in wide
  narrow mouthed glass bottles with a rubber
  stopper.
• Before transferring the sample into bottle first
  add the preservatives (formalin, mercuric
  chloride, potassium dichromate) to avoid
  subsequent contamination of the sample

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4. Weighing

• This is essential step in accounting for milk
  receipts and disposal, making payment for milk
  etc.
• Milk in cans are measured by weight. The milk
  in cans is dumped into the weigh tank it is
  mounted on scales the scale dial is set at zero
  when the empty tank is on the scale, thus
  enabling the operator to make a direct reading of
  the weight of the milk
• The milk in tanker may be measured by volume
  by passing it through a flowmeter. The
  measurement converted into weight by multiplying
  the volume with agreed density. Measurement by
  milk by weight gives accurate results by avoiding
  foam unlike in volume method.

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Testing

•  Apart from platform test in order to provide
  good quality of milk in-terms shelf-life, payment
  based on fat content etc. milk is tested in
  laboratory. E.g.
• Dye reduction test.
• DMC Direct Microscopic Count.
• SPC Standard Plate Count Fat/SNF content.

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Pre heating

•  The term pre-heating refers to heating before
  the certain operation Such as(filtration,
  centrifugation).
• The milk is preheated for efficient
  filtration/clarification.
• Pre-heating is essential, if incoming milk is
  cold as otherwise the flow of milk is hampered.
• As the temperature of milk increases, the
  viscosity decreases and more efficient
  filtration/clarification results.
• The usual temperature is 35-40C
• Equipment used may be plate/tubular heater

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Clarification

• Clarification removes the suspended, foreign
  particles by centrifugal sedimentation Such as
  leucocytes, udder tissues, other large cells and
  fine dirt.
• Removal of clarifier slime does not affect the
  composition of milk to a significant extent
  usually it may be 0.01.
• The objective of clarification is to improve the
  appearance and marketability of milk.
• Bactofugation is the process of removing 99 of
  the bacteria in the milk by centrifugal force.

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Location of clarifier in processing line
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Difference between cold and warm clarification

• a) Cold milk clarification
• Efficiency is lower since viscosity of milk is
  high.
• Operation time is more because less free casein
  particles are thrown out as slime.
• Quality of the processed milk is better as dirt
  is removed from the milk.
• b)Warm milk clarification
• Efficiency is higher due to lower viscosity of
  milk.
• Running time is reduced because of rapid free
  slime build-up
• Operation of the entire system is more critical
  with a high pressure drop through the clarifier
  on one side of the pump and suction on the other
  side.

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Factors affecting clarification

• Viscosity
• The viscosity of milk is an important factor to
  be considered in clarification, since the
  suspended foreign particles are removed by
  centrifugal sedimentation. Settling of
  particles by centrifuging depends upon their
  size, density and viscosity of the fluid in which
  they are suspended.
• TemperatureIn general, the viscosity of liquid
  decreases as the temperature increases. Hence,
  milk is usually heated to a temperature of
  32-35C before it is subjected to clarification.
  A high temperature must be avoided as it
  adversely affects the creaming property of milk.

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• Microbial loadThe type and state of microbe
  influences the efficiency of clarification. The
  bacterial spores being denser are thrown into the
  slime more easily.
• Bowl speedThe higher the speed, the better is
  the efficiency as the centrifugal force is
  directly influenced by the speed of the bowl.

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Cooling and storage

• As soon as milk is received from the plant, it is
  chilled at 5C/below and stored because to
  prevent deterioration in its bacteriological
  quality during storage period.
• Methods of Cooling
• Surface Cooler
• Plate Cooler
• Inter tubular Cooler
• Jacketed Cooler

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continuation

• Storage of raw as well as pasteurized milk is
  important.
• Therefore design of storage tank such a way that
  it is easily cleanable/ease in sanitation,
  insulated with refrigerant and adequate agitation
  for homogenous mixing.
• The main objective of storage of raw milk is to
  facilitate bulking of the raw milk supply, which
  will ensure uniform composition.
• Storage Tank Horizontal Vertical Storage Tank

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Standardization

•  It refers to the adjustment of fat content of
  milk or milk product, by addition of cream or
  skim milk as appropriate to obtain a desired
  value to meet legal or other requirements.
• E.g. Toned Milk SNF 8.5 Fat 3.

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Objective

• To comply with the legal requirements for
  particular milk/dairy products.
• To provide the consumer with a uniform product.
• To ensure economics in production.

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Pasteurization

• It is the thermal inactivation of microorganisms
  at temperatures around 72-78C for specific time
  period, which improves the hygienic quality of
  milk and achieves a certain level of
  preservation.
•  After pasteurization, the milk is immediately
  cooled to 5C or below.
• The main 2 objective of pasteurization of milk
  are
• To improve the keeping quality of milk by
  destruction of almost all spoilage organism
  (85-99)
• The main objective is to kill pathogens to avoid
  health hazard

TEMPERATURE TIME PROCESS
72C 15 SECONDS HTST
62.8C 30 MINUTES LTLT
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Drawbacks of Pasteurization

• It diminishes the cream line or cream
  volume. Pasteurized milk may increase the
  renneting time. It fails to destroy bacterial
  toxins In India, pasteurization is not
  necessary as milk is invariably boiled on receipt
  by the consumer

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Homogenization

• Homogenization can be defined as the process in
  which fat globules in milk are broken down to a
  size small enough to prevent the formation of a
  cream layer.
• Homogenizer is a machine, which disintegrates the
  fat globules of milk.
• It involves passing the milk through a high
  pressure homogenizer, which reduces the size of
  the fat globules and distributes them evenly
  throughout the milk.
• Homogenization improves the consistency,
  stability, and creaminess of the milk, giving it
  a smoother texture.

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cooling

• After homogenization of milk, it is cooled to a
  low temperature of 5C or below
• It is done to inactivate microbial growth and
  increase shelf life.

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BOTTLING PACKING

• Milk after undergoing number of processing like
  pasteurization, homogenization etc. is packed in
  bottles/packets followed by storage.
• Then stored at low temperature. (of 5C or below
  ).
• Different Packaging Materials(i) Glass (ii)
  Plastics (iii) Coextruded and multilayered
  packaging materials

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Storage

• The processed or fluid milk is stored with its
  packaging material at low temperatures generally
  at 5 or lt C.
• However raw milk in industries is stored in
  various tanks such as
• Vertical/Silo tanks
• Horizontal tanks

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References

• Market Milk Lesson 16. RECEPTION OF MILK
  (iasri.res.in)
• Market Milk Lesson 18. FILTRATION AND
  CLARIFICATION (iasri.res.in)
• Market Milk Lesson 21. BACTOFUGATION
  (iasri.res.in)
• Market Milk Lesson 26. PRINCIPLES OF HEAT
  TREATMENT (iasri.res.in)

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• Thankyou