Pasteurization

History

The term pasteurization has been coined after the name of Louis Pasteur of France, who in 1860-64 demonstrated that heating wine at a temperature between 122 to 140⁰F killed the spoilage organisms and help in its preservation. The application of this process gives rise to the new term pasteurization.

Definition

The term pasteurization, as a applied to market milk today, refers to the process of heating every particle of milk to at least 63⁰C for 30min, or 72⁰C for 15sec (or to any temperature-time combination which is equally efficient), in approved and properly operated equipment. After pasteurization, the milk is immediately cooled to 5⁰C or below.

Objectives

To improve the keeping quality of milk by destroying almost all spoilage organisms and to render milk safe for human consumption.

Objections

1. Pasteurization encourages slackening of efforts for sanitary milk production;
2. It may be used to mask low-quality milk;
3. It reduces the "Cream line" or "Cream volume";
4. It diminishes significantly the nutritive value of milk;
5. Pasteurized milk will not clot with rennet;
6. Pasteurization may be carelessly done; it gives a false sense of security;
7. It fails to destroy bacterial toxins in milk;
8. In India this is not necessary as milk is invariably boiled.

Methods of pasteurization

• In-the-bottle pasteurization

In this case bottles filled with raw milk and tightly sealed with special caps are held at 63 to 66⁰C for 30min. Then the bottles passed through water space of decreasing temperature, which cool both the product and the bottle. In this case there is greater risk of bottle breakage also special types of water-tight caps required to be used. One of the advantages is that it prevents the possibility of post- pasteurization contamination.

• Batch/Holding pasteurization/Low temperature long time method

In this case the milk is heated to 63⁰C for 30min and promptly cooled to 5⁰C or below and thus heating is done indirectly. The heat moves through a metal wall into the product for heating, and out of the product for cooling. The Pasteuriser may of 3 types.

1. Water-Jacketed vat
2. Water-Spray type
3. Coil-vat type
1. High temperature short time (HTST) pasteurization

In this case large volumes of milk are handled and it gives a continuos flow of milk which is heated to 72⁰C for 15 sec and promptly cooled to 5⁰C or below.

Advantages

1. Capacity to heat treat milk quickly and adequately, while maintaining rigid quality control over both the raw and finished product;
2. Less floor space required;
3. Lower initial cost;
4. Milk packaging can start as soon as pasteurization begins, thus permitting more efficient use of labour for packaging and distribution;
5. Easily cleaned and sanitized;
6. Development of thermopiles not a problem;

Disadvantages

1. Complete drainage is not possible;
2. Great accumulation of milk-stone in the heating section.
3. Pasteurization efficiency of high-thermoduric count raw milk is not as great as it is when the holder system is used.
1. Electric pasteurization
2. Vacuum pasteurization

This refers to pasteurization of milk and there reduced pressure by direct steam. The equipment used is termed as ‘Vacreator’ and the process hence is known as ‘Vacreation’

3. Stassanization

This method consists of tubular heat exchanger consisting of 3 concentric tubes. The principle of its operation is the heating of milk to the desire temperature by passing it between two water-heated pipes through the narrow space of 0.6 to 0.8 mm. The milk is heated to above 74⁰C for 7sec and promptly cooled as usual.

4. Ultra high temperature pasteurization

This method consists of temperature-time combinations of 135 to 150⁰C for no hold (a fraction of second). The success of this method depends on immediate aseptic packaging.

5. Uprization

Uprization term means ‘Ultra- pasteurization’ where in milk is heated with direct steam up to 150⁰C for a fraction of second and thus the process is continuos.

6. Flash pasteurization

In earlier days, this term was used for what is today called ‘HTST’.

The formulation of the standards of pasteurization includes following points.

• Bacterial destruction

Mycobacterium tuberculosis, being considered the most heat resistant among packages, was chosen as the index organism for pasteurization.

• Cream line reduction

The cream line is reduced progressively with increase in the temperature-time of heating.

• Phosphatase inactivation

It includes the complete destruction of Phosphatase by pasteurization. The phosphatase test is used to detect inadequate pasteurization.

Thus the standards of pasteurization were made so as to insure complete distraction of pathogens, negative phosphatase test and least damage to the cream line.