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What is Milk Pasteurization?


In the year 1860, there was a well known french microbiologist /biologist & chemist named "Louis Pasteur", who is well known for his discoveries regarding disease and it's prevention. He is famous for his well-known germ theory of disease and one of the main founders of bacteriology.
Pasteur continued studying the growth of the microorganisms and the way he can prevent it's growth so that the prevention of disease of the spoilage of food is prevented.
He came across a super great idea of a process that bears his name too i.e, Pasteurization.
Pasteurization is the process which is used to kill the microbe like lactobacillus and yeasts with the help of the heat usually less than 100 degree Centigrade ( 212 degree F). It is used for both packaged and non-packaged food like beer, fruit juice, milk etc.
Pasteurization is way different from the sterilisation process as it only deactivates the microbial physiology and stops it to grow further, it also deactivates the enzymatic activity (methylesterase and polygalacturonase) of the microbes which are responsible for the spoilage of any food items.
Pasteurization hence is not an effective way to kill spores of microbes as the killing of spores requires a much higher temperature of it can be killed by autoclaving as like steam sterilization.

Equipment Pasteurisation :

Several food items like beer, milk, baby foods, fruit juice etc are generally packed in the plastic or steel container to prevent thermal shock.
Some medical equipment like scissors, scalpels, respiratory anaesthesia is often sterilized at 79 degree centigrade for 30 minutes.
Most of the liquid products are sterilized with the continuous system and are very well packaged directly without any involvement of the microbes. Plate heat exchangers which are made up of stainless steel which is used to pasteurise liquid items. These heat exchangers provide good heat treatment uniformly over all the products.
Shell or tube heat exchangers are also made of stainless steel but are designed in concentric ways. Any of the food item especially non- Newtonian food items are allowed to pass through the while heating or cooling and is pasteurised well.

"Milk Pasteurization"

Fresh milk is rich in moisture content as it contains 85% of the water in it. The moisture in the culture is believed to be a very suitable medium for microbial growth. Milk is also used in several microbiological lab experiments as a culture medium, especially for lactobacillus bacteria.
Milk pasteurization is thus, a very needed step to be performed as the milk starts getting spoiled after 4-5 hours of milking. Though pasteurization may reduce the concentration of certain vitamins like B12 and E it is not scientifically proven yet.
Pasteurization of milk is done to make milk stays for a longer period and safe to drink. Pasteurization increases its spoilage period it is done at 70 degree centigrade for 15 seconds. In this, we give the heat treatment to the milk to kill or eradicate the microbes present in it.
Soon after pasteurization of milk, it is packaged in an airtight packaged plastic bag or bottle which creates a barrier between the microbes present in the surrounding and between the packaged milk.
The high treatment of pasteurization shouldn't exceed 25 seconds at 70 degree centigrade. It can lead to the denaturation of the protein content of the fresh milk.

Methods of milk pasteurization at different temperature :

1- Microwave volumetric heating (MVH) Pasteurization

is the latest pasteurization technique. In this technique product or any food, the item is given extremely gentle heat treatment for a shorter period. It is done with the use of the microwave oven to evenly heat the solid or the liquid items so that it would prevent the spillage of that item.

2- Ultra-high temperature (UHT) Pasteurization

is the technique which is generally used to pasteurize full cream milk, it helps in increasing the shelf life of the milk. UHT pasteurization is done at an extremely high temperature of 135 degree centigrade to 150 degree centigrade for 1 to 2 seconds. So, UHT is hence proved to be a very effective pasteurization technique amongst all techniques.

3- Low-temperature long time (LTLT) Pasteurization

is the low-temperature Pasteurization technique in which the milk is pasteurised at 63 degree centigrade for 30 minutes. It thickens milk's consistency and makes it very good in texture. This LTLT Pasteurized milk works well for baking and cooking purposes or for preparing yoghurt.

4- High-temperature short time (HTST) Pasteurization

is a blinking pasteurization technique done in a short period for 10-15 seconds but the heating of milk is done at the temperature of 71.5 degree centigrade. This is the safest pasteurization technique and increases the shelf life of the food items or beverages by one or two more weeks. This technique is highly used for commercial purposes. It also helps in killing microbes which can survive at high temperatures.

Steps of pasteurizing milk :

1) Preheating process:-

Normal milk is brought to the process of preheating of milk at about 40 degree centigrade. This step is necessary for standardization so that the milk is standardized and the butterfat is separated and is uniformly distributed all over the milk.

2) Clarification process:-

The most important step done for clearing up the milk impurities. A large centrifugal clarifier is used along with the tank which removes all solid foreign particles from it.

3) Standardization process:-

Standardization of the milk is necessary so that all over the milk has a uniform distribution of its butterfat content so that the leftover milk won't look skimmed.

4) Homogenisation process:-

Homogenization of milk is done for making milk's density uniform by breaking large lipid molecules into smaller ones so that the smaller droplet will dissolve in the milk and resulting in the thicker consistency of the milk.

5) Heating process:-

Heating of the milk which is the main step of pasteurization, it is done according to the product and the time as of UHT, LTLT, HTST and MVH techniques. It helps in destroying the microbes and prevents us from any of the food poisonings or any stomach infections.

6)Holding section:-

Pasteurisation technique tanks have tubes/channels to pass out the milk for the next cooling process. It takes almost 15-16 seconds for the milk in those channels to bring milk to the room temperature.

7)Cooling process:-

The cooling process should also be done immediately after receiving it from the holding section, coolant is used to lower the temperature of the pasteurized milk to 4 degree centigrade. Cooled milk is then moved to the packaging section.
8) Packaging & storage section:- The pasteurised milk is lastly moved to the packaging section whether it is bottled or packaged in plastic bags. Then it is stored at the extremely low temperature less than 4 degree centigrade for the safest storage.

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