Pasteurization of Milk is a procedure that uses moderate heat, often less than 100 °C (212 °F), to kill microorganisms and increase the shelf life of some packaged and unpackaged goods (such as milk and fruit juice).
To monitor food safety and quality, there is an urgent need for quick processes that are relevant to process control.
A procedure protects food by eliminating or inactivating organisms that cause food to deteriorate, including vegetative bacteria but excluding bacterial spores.
The procedure has the name of the French scientist Louis Pasteur, whose work in the 1880s showed that heating would render undesirable microbes in wine inactive.
Pasteurization is now widely employed in the dairy sector and other food processing industries to accomplish food preservation and safety.
Different Types of Thermal Processing Methods
The bacteria that caused TB was the initial target organism (Mycobacterium bovis or M. tuberculosis). The minimum pasteurization temperature was raised in the 1950s to kill Coxiella burnetti, a bacteria that causes Q-fever and is a little more heat-resistant.
Thermization: Warm the milk to a temperature of 57 to 68 degrees Celsius and hold for 15 minutes. Thermization destroys harmful germs while leaving beneficial ones in the product. Low temperatures have no effect on the milk’s flavor or composition.
Batch Pasteurization: Pasteurization in batches is often referred to as LTLT (low temperature, long time) pasteurization. Milk is heated for 30 minutes to 63 °C. The structure and flavor of the milk protein are altered due to the prolonged storage period.
Flash pasteurization: High-temperature, short-time (HTST) pasteurization is another name for flash pasteurization. For 15 to 20 seconds, heat the milk to a temperature of 74 °C to 76°C.
Ultra-high temperature (UHT): Pasteurization at an ultra-high temperature (UHT) involves heating milk to temperatures between 135 °C and 140 °C for 2–4 seconds. The Q-fever-causing Coxiella burnetii is targeted by the intense heat. All vegetative forms of bacteria are destroyed by heat, allowing milk to last nine months.
Cannedsterilised: In an autoclave or other specialized treatment room, canned milk products are wetly sterilized. For 10 to 20 minutes, heat to 115 to 121 degrees Celsius.
Milk Pasteurization Definition
The process of pasteurizing milk involves heating milk (or milk products) to a certain temperature for a set amount of time without recontamination.
The goal pasteurization program temperature is often established by how heat-resistant the spoiling bacteria are.
Methods Used in Pasteurization of Milk
High-Temperature Short Time (HTST) Pasteurization
Flash pasteurization is another name for this process.
Coxiella burnetii, the pathogen that is most resistant to heat in raw milk, is killed by flash pasteurization, which entails heating milk to 71.7 °C for 15 seconds.
It is always safe to operate with a range of temperatures since it is physically impossible to heat the milk to that precise degree. You may safely heat the milk for 15 to 20 seconds at a temperature of 72° to 74 °C.
This will guarantee that the milk is heated to the proper temperature consistently.
Systems that use continuous pasteurization are best suited for this technique.
Milk that has been flash-pasteurized lasts between 16 and 21 days. Some manufacturers purposefully shorten the number of days it takes to get their items off the shelves for business reasons.
Low-Temperature Long Time (LTLT) pasteurization
Here, pasteurization temperatures are lowered to 63 °C and maintained there for 30 minutes.
The extended holding time changes the milk proteins’ structures, making them more suitable for yogurt production.
The milk is kept in a jacketed vat for efficient pasteurization in this procedure, which is excellent for batch pasteurization.
Batch pasteurizers come in various styles that are appropriate for household and commercial use.
Ultra-High Temperature (UHT) Pasteurization
This pasteurization technique uses a totally closed system. Throughout the whole procedure, the product is never even briefly exposed.
In order to aseptically package milk or cream for storage, it must first be heated to between 135 °C and 150 °C for one to two seconds. After that, it must be quickly chilled.
UHT pasteurization is still the most widely used milk preservation technique for secure and stable milk, notwithstanding the threat of Millard browning.
Steps of Pasteurization of Milk
Milk chilling
When working with huge quantities of milk, chilling is an essential step, even if pasteurization is not a part of it.
At temperatures above ambient, milk exits the cow’s udder, encouraging fast bacterial proliferation that hastens deterioration.
Storing products between 2 and 5 degrees Celsius stops bacterial growth and metabolism.
Before thorough pasteurization starts, storing at low temp provides a good option.
Pre-heating (regeneration) and Standardization Stage
The cold milk is bulked before being heated to roughly 40 °C to make it easier to separate the butterfat during standardization.
The system employs regenerative heating, which means it warms up the incoming cold milk using the heat from the previously pasteurized milk. The pasteurized milk is cooled by the chilled milk in a countercurrent flow.
The goal of standardization is to produce a product with a consistently high butterfat content.
Clarification stage
Clarification is necessary to get rid of all extraneous material from the finished product.
Milk is strained through metallic tube filters to eliminate large solid particles.
Milk is thoroughly cleaned of all dirt and contaminants using a centrifugal clarifier (different from the one used for standardization).
Since the filters are often installed as parallel twins, processing can continue while one filter is being cleaned.
To prevent the development of germs, clean the filters often (every 2 to 10 operating hours, depending on the level of filth).
Standardization stage
To produce a product of consistently high quality for the market, it is crucial to standardize milk fat. Different items are preferred by various consumers.
There are clients who just want to drink skim milk, and there are others who want low-fat milk. Some people like high-fat milk, while others will only drink homogenized milk.
Normalisation is required to make sure that all the clients are cared for.
Once more, it is through the standardization process that you can distinguish between the butterfat needed to make cream and other fat-based goods like ghee and butter.
Homogenization stage
To prevent cream separation, milk fat globules are physically broken down into small droplets during homogenization.
Because lowering the size of the fat droplets also improves their density in the milk, they do not rise in a milk column.
All the fat globules are divided into minuscule droplets by a milk homogenizer operating at between 100 and 170 bars, which raises the degree of fat integration in the milk.
As a result, the milk fat is still evenly dispersed throughout the milk.
Heating section
uses steam heat to elevate the milk’s temperature from around 60 °C to the necessary 72 °C, which is necessary in killing Clostridium botulinum spores.
Across the PHE plates, the steam and milk conduct a counter-current heat exchange.
The flow diversion valve is controlled by a temperature sensor at the section’s conclusion.
Any milk that does not reach the necessary temperature is sent back to the heating area to be heated up again.
Holding section
Following heating, milk enters holding tubes whose lengths have been adjusted with the milk flow rate to guarantee that milk stays in the tubes for at least 16 seconds. All the milk must retain the necessary pasteurization temperatures at the ends of the tubes.
In the event of a breach, a sensor will open a flow-diverting valve, sending milk back to the heating area where it will be heated to the appropriate temperature.
When the milk reaches the proper temperatures at the end of the holding tubes, it flows back to the regeneration section, where it is cooled down to roughly 30 °C while being heated to warm the incoming cold milk.
Cooling/chilling section
Pasteurized milk flows to the PHE’s cooling portion after undergoing regenerative cooling, where chilled water and PHE coolant drop the milk’s temperature to 4 °C.
The aseptic packaging equipment receives the cooled milk and pumps it to the cold room for storage.
Significance of Pasteurization of Milk
The following justifications justify the need for proper pasteurization:
The major purpose of milk pasteurization is to kill harmful microorganisms that might have a public health risk. These germs are eliminated, making the product safe for use by the general population.
Secondly, pasteurization removes damaging microorganisms and enzymes that might cause spoilage of the product. As a result, milk has a longer shelf life.
The product needs to be able to last for longer periods of time without the need for expensive storage equipment. The product’s shelf life will be increased by removing spoiling bacteria and enzymes during pasteurization.
