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
- 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
- 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.
- 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.
- 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.
- 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.
- 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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