7 Various methods of pasteurization

Pasteurization refers to the process of heating every particle of milk or milk of the different classes to atleast 63°C (145°F) for 30 minute or 72°C (161°F) for 15 seconds or an approved temperature and time combination that will serve to negative phosphatase test, the milk is immediately cooled to 5°C (41°F) or below.

7 Various methods of pasteurization

  1. Batch pasteurization / low temperature long time pasteurization (LTLT)
  • Every particle of milk is subjected to a temperature of 63°C for 30 min followed by prompt cooling to 5°C or below.
  • It has 3 types:
    • Water jacketed type: Steam or hot water passing through double jacket of vat. Foam heater is used to prevent surface cooling
    • Water spray type: Spraying of the hot water
    • Coil vat type: Heated and cooling by horizontal and vertical turning coil
  • Advantages
    • It is useful for handling small quantity of milk.
    • It does not involve sophisticated equipment.
    • Technically trained persons are not required as its operation is easy.
    • Milk is not wasted during this process.
  • Disadvantages
    • There is possibility of outside contamination.
    • Time taken for pasteurization is too long as there is no regenerative heating and cooling. Hence growth of thermophilic organisms is encouraged.
    • Automatic control to check the operation is not possible.
    • This occupies more space and in place-cleaning is not convenient.
    • It can not handle large quantity of milk and operation cost per litre of milk handle is more.

2. High temperature short time pasteurization (HTST):

  • Heating of milk – 72°C for 15 sec. – cooling to 5°C or below.

1) Tubular heat exchanger: Shell-and tube and concentric tubes.

  • In shell-and –tube heat exchanger: No. of small tubes carrying milk – passing to large tubes where heating/cooling medium circulated.
  • Concentric tube heat exchanger: Inner and outer tube carrying the heating/cooling medium and middle tube carrying the product.

2) Plate heat exchanger: The corrugated stainless steel plates held (3 mm) aprat are joined together by non-absorbant rubber  gaskets or seal.

  • Advantages
    • This is useful for handling large quantity of milk.
    • The capacity can be increase by increasing the number of plate heat exchanger.
    • The energy required for heating and cooling is saved by the regenerative process of this method.
  • Disadvantages
    • This not suitable for handling small quantity of milk.
    • Gaskets used between the plates must be given constant attention.
    • Complete drainage is not possible as approximately 10% milk retained in between the plates.
    • There are chances of formation and accumulation of milk stones.
    • Margins of safety in the product sanitary control are narrow.
    • It required trained operator.
    • Survival of thermoduric organisms is possible.

3. Vacuum pasteurization

  • Pasteurization of milk/cream under vacuum – Vacreation.
  • The advantage of this process is to remove off flavour from milk as well as cream.
  • The process has been found more suitable for pasteurization of cream meant for butter making.
  • The machine used for vaccum pasteurization is known as vacreator which is invented in New Zealand by M/s. Murry Deodorizers Ltd.

4. Flash pasteurization

  • The temperature of milk is raised to 80°C for practically no holding period.
  • This process destroyed all pathogenic organisms that might be present in milk.
  • The major advantages of this process are the reduction in nutritive value of milk is less in this methods as compared to other methods.

5. Ultra high temperature treatment (UHT)

  • Every particle of milk is subjected to a temperature time combination of 135°C – 150°C without holding.
  • The success of this treatment depend upon aseptic packaging in tetra pack.
  • UHT is 2 types.
    • Direct heat treatment: either the steam is injected into the  milk or milk is infused into the steam.
    • Indirect heat treatment: either by plate heat exchanger or tube heat exchanger

6. Ultra pasteurization (Uperisation)

  • The process of uperization is one of the recent inventions of the market milk industry.
  • The process has been developed in Switzerland.
  • In this process milk is heated with a direct steam up to 150°C for a fraction of a second.

7. Stassanization

  • The credit of developing this process of pasteurization goes to a French scientist Henri Stassno who invented the process in France.
  • The process is now in use to a considerable extent in milk plants of France, Denmark, Italy and certain other countries.
  • The principle of its operation is heating of milk to the desired temperature by passing it through two water heated pipes, through narrow space of 0.6 to 0.8 mm.
  • The milk is force through the narrow space which comes in contact with heating surface. The temperature of milk is raised to about 74°C for 7 seconds and immediately cooled to 4 to 5°C.

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