Milk Pasteurization Definition, Procedure, Types, Purpose

What is pasteurisation?

Pasteurisation was developed by an French Scientist known as Louis Pasteur during the nineteenth century. Pasteur realized that warming milk up to a high temperature , then cooling it quickly prior to packaging or bottling could preserve it for a longer time.

Nowadays, pasteurisation is commonly used in the food and beverage industry. It is the most commonly used form of heat treatment applied to milk in Northern Ireland. Pasteurisation assures that the milk is safe for consumption (by getting rid of any bacteria) and can also help prolong the shelf-life of milk.

Pasteurisation is the process of warming milk until 71.7degC for minimum 15 seconds (and not longer than). Due to the nature of the heat treatment, it is sometimes called the ‘High Temperature Short Time’ (HTST) process. After the milk is heated, it is rapidly cooled to less than 3 degrees Celsius. The machine used to cool and heat the milk is referred to as”heat exchanger”.

Once the milk is pasteurised, it’s either stored in bottles or packages for sale to consumers.

What is Milk Pasteurization?

There is a widespread and urgent requirement for swift procedures that can be used for process control, in order to control the quality and safety of food products.
Pasteurization is the process by which packaged and unpackaged food items (such as juices and milk) are treated using moderate heat, typically less than 100 degrees Celsius (212 degF) to eradicate bacteria and extend shelf-life.

The process protects food by eliminating or inactivating the organisms which contribute to spoilage which includes vegetative bacteria, but not spores from bacterial organisms.
The process was named in honor of it’s creator, French science researcher Louis Pasteur, whose research in the 1880s showed that thermal processing could destroy harmful microorganisms found in wine.
Nowadays, pasteurization is employed extensively within the dairy sector as well as other industries that process food to ensure food preservation and ensure food safety.

Definition of Milk Pasteurization

Pasteurization of milk is the procedure of heating milk (or the milk product) to a specified temperature for a certain time without recontamination throughout the entire process. The temperature of the predetermined range is usually based on the resistance to heat generated by spoilage microorganisms that the program is aiming to eliminate.

The Purpose of Pasteurization

Increase the safety of milk for consumers by eliminating microorganisms responsible for causing disease (pathogens) that could be found in milk.
To improve high-quality milk products by eliminating spoilage microorganisms and enzymes which cause a decrease in the quality and shelf-life of milk.

Types of Thermal Processing Methods

In the beginning, the target organism was the bacterium responsible for tuberculosis (Mycobacterium bovis or M. tuberculosis). In the 1950’s the minimum temperatures for pasteurization were increased to kill a resistant to heat. The organism was then in contact with raw milk. Coxiella burnetti. It can cause Q-fever.

Thermization: Warm the milk between 57 and 68 degrees Celsius. Hold until 15 mins. Thermization destroys pathogenic bacteria but leaves the healthy bacteria in the milk. The lower temperatures don’t affect the structure and flavor of the milk.
Batch pasteurization: Batch pasteurization is also referred to as low-temperature, long-time (LTLT) pasteurization. The milk is heated to 63°C in 30 mins. The prolonged holding time is the reason for the change in protein structure of the milk and its taste.
Flash pasteurization: Flash pasteurization is also referred to as high-temperature, short-time (HTST) pasteurization. The milk is heated between 72degC and 74degC for 15 to 20 minutes.

Ultra-high temperature (UHT) pasteurization: Heat the milk between 135degC to 140degC over two to four minutes. The intense heat is aimed at Coxiella burnetii which is responsible for Q-fever. This heat destroys varieties of bacteria, and the milk is able to endure for up to 9 months.
Canned sterilization: This is a wet treatment of canned milk products in an autoclave/specialized treatment chamber. Temperature should be between 115degC and the temperature of 121degC over 10 to 20 minutes.

Types of Thermal Processing Methods — Image Source: https://www.zwirnerequipment.com/blog/methods-of-pasteurization/

Methods Used in Milk Pasteurization

1. High-Temperature Short Time (HTST) Pasteurization

This kind of pasteurization is also referred to by the name flash pasteurization. Flash pasteurization involves heating milk up to 71.7degC within 15 seconds in order to eliminate Coxiella burnetii. It is the most resistant pathogen to heat in raw milk. Because it is technically impossible to heat the milk to this exact temperature, it is safe to work within the range of temperatures. To ensure safety it is recommended to warm the milk between 72degC and 74degC over 15 to 20 minutes. It will guarantee that milk gets evenly heated at the correct temperature.

This method is best for continuously pasteurization equipment. Pasteurized milk that is flash pasteurized will last between 16 to 21 days. To meet commercial requirements certain manufacturers deliberately reduce the amount of time needed in order to take the products off of their shelves.

2. Low-Temperature Long Time (LTLT) pasteurization

In this case, the temperatures utilized for pasteurization are lowered to 63degC , and kept until 30 mins. The longer time of holding alters the structure and structure of milk proteins, making them more suitable for the production of yogurt.

This is the best method for batch pasteurization, where the milk is kept in a jacketed vessel for an efficient pasteurization. There are a variety of designs for batch pasteurizers on the market that can be used for commercial and residential usage.

3. Ultra-High Temperature (UHT) Pasteurization

It is a completely closed pasteurization technique. The product is not exposed for even less than a minute throughout all the process. It involves heating cream or milk up to temperatures ranging from 135degC to 150degC for a period of one to two seconds, and then cooling immediately before packaging it in an hermetic (air-tight) container to be stored. Despite the possibility that comes with Millard the browning process, UHT is still the most well-known method for preserving milk to ensure stable and safe milk.

4. Ultra Pasteurized

Not to be mistaken for UHT, Ultra Pasteurized (UP) milk is heated with industrially-grade sterile equipment, however, it isn’t considered to be as sterile since it isn’t hermetically sealed. The milk is heated up to 280 degrees Fahrenheit (138 degrees Celsius) for minimum two seconds, after which it is rapidly cooled down. Because the milk isn’t completely sealed off, it needs to be refrigerated, with an average shelf-life of 30 to 90 days.

Steps of Pasteurization

The general procedure of mil Pasteurization are;

1. Milk chilling

Chilling isn’t a pasteurization procedure, but it is an essential step to take when handling large amounts of milk. The cow’s udder is at temperatures higher than average, which causes rapid bacterial growth that speeds the process of spoilage. But, reducing the temperature from 2deg to 5deg C can stop the growth of bacterial and metabolism. This helps to get an advantage in maintaining the purity before proper pasteurization begins.

2. Pre-heating (regeneration) and Standardization Stage

After bulking, the milk is heated up to around 40 degrees Celsius to allow for the effortless separation of butterfat during standardization. The system employs Regenerative warming, i.e., it utilizes the heat of the pasteurized milk to warm up the newly chilled milk. It is chilled, through an opposite flow, cools to pasteurize it. The goal in standardization would be to produce an item with a uniform amount of butter-fat.

3. Clarification stage

Clarification is crucial to remove any foreign matter that is present in the milk. Massive solid particles can be eliminated by straining milk through metallic tubular filters. Clarifiers that are centrifugal (not the one used to standardize) is utilized to eliminate all sediment and soil from milk.

The filters, typically installed in parallel twins, permit continuous processing since one filter is cleaned when the other one is operating. Make sure to clean the filters frequently (between 2 and 10 hours of operation, based on the degree in dirt) to stop the development of bacteria.

4. Standardization stage

It is essential to standardize the milk fat in order so that you get an item of the same high quality on the market. Different consumers prefer different products. There are those who take skim milk only, whereas there are others who drink low-fat milk. There are people who consume standard milk and some favor milk with high fat.

Standardization is essential in order to make sure that people who purchase it are satisfied. In addition, it is in the course of standardization that you can cut off the butterfat used to make cream as well as other products made from fat, such as butter and Ghee.

5. Homogenization stage

Homogenization is a process that involves breaking down milk fat globules to tiny droplets in order to prevent cream separation. tiny droplets of fat do not expand in the milk column because shrinking their size increases their density within the milk. A homogenizer for milk operating at a rate of between 100 and 170 bars breaks up all the fat globules in tiny drops that boost the amount of fat integration in milk. In the end, the milk fat is evenly dispersed in the milk.

6. Heating section

Make use of steam heat to increase the temperature that the milk is at 60degC up to 72degC to kill Clostridium botulinum microspores. Steam exchanges heat with the milk over PHE plates. PHE plates, in an anti-current movement. If, at the end, there is this section is present, there is a temperature sensor that regulates the valve for flow divert. Milk that fails to meet the required temperature is diverted towards the warming section, until it reaches the desired temperature.

7. Holding section

After heating, the milk flows through the holding tubes, whose lengths are calibrated according to the rate of flow to ensure that milk lasts minimum 16 seconds to enter the tubes. The milk must be kept at the necessary temperatures of pasteurization at the top of each tube. If there is an incident an alarm will be triggered by the valve for flow divert, which will take your milk to the heating unit in order to get the milk back to the desired temperature. When the milk reaches the temperature required at the top of the tube holding the milk flows back to regeneration section, which heats the milk as it is brought in, as it cools down to 30 degrees Celsius.

8. Cooling/chilling section

After the regenerative cooling of pasteurized dairy then it is transferred to the cooling area of the PHE where chilled PHE coolant and chilled water reduces the temperature of pasteurized milk by 4 degrees Celsius. The chilled milk is transported to the packaging equipment for aseptic packaging, and later freezing in the room.

Significance of Pasteurization

Proper pasteurization is required to meet the following requirements:

The main goal of pasteurization in milk is to eliminate pathogenic bacteria that could pose an impact on public health. Through the destruction of microorganisms the milk is safe for consumption by the public.

Additionally, pasteurization kills harmful enzymes and bacteria that can cause the product to spoil. This prolongs the shelf-life of the milk.
It is essential to make sure that the product will be stored for longer durations without the expense of storage equipment. Pasteurization is a way to stop spoilage-causing enzymes and bacteria and prolong the shelf life that the food product has.

Pasteurization conditions used for milk products

Pasteurization Type	Typical Product	Typical Storage	Temperature	Holding Time
Batch, vat	Milk	Refrigerated	145°F (62.8°C)	30 min
“	Viscous products, or products with more than 10% fat or added sweetener	“	150°F (65.6°C)	30 min
“	Egg nog, frozen dessert mixes	“	155°F (68.3°C)	30 min
Continuous, high temperature short time (HTST)	Milk	“	161°F (71.7°C)	15 sec
“	Viscous products, or products with more than 10% fat or added sweetener	“	166°F (74.4°C)	15 sec
“	Egg nog, frozen dessert mixes	“	175°F (79.4°C)	25 sec
“	“	“	180°F (82.2°C)	15 sec
Continuous, higher heat shorter time (HHST)	Milk	“	191°F (88.3°C)	1 sec
“	“	“	194°F (90°C)	0.5 sec
“	“	“	201°F (93.8°C)	0.1 sec
“	“	“	204°F (96.2°C)	0.05 sec
“	“	“	212°F (100°C)	0.01 sec
Continuous, Ultrapasteurization	Milk and cream	Refrigerated, extended storage	280°F (137.8°C)	2 sec
Aseptic, ultra high temperature (UHT)	Milk	Room temperature	275-302°F (135-150°C)	4-15 sec
Sterilization	Canned products	“	240°F (115.6°C)	20 min

High temperature short-time (HTST) Pasteurization Process of milk

The first time this was developed by A. P. V. Co. in the United Kingdom in 1922. The HTST pasteurizer provides an uninterrupted stream of milk. The process of HTST involves heating milk to 72 to 750 C and a 15 second waiting time, before cooling.

One of the primary benefits of batch and continuous system is the fact that it can be reclaimed by means of regeneration. Regeneration efficiency of up to 95% are possible this means that a pasteurized item that requires heating to 720C could be heated to more than 680C via regeneration when the milk’s initial temperature is 4 degrees C. Even though high regeneration efficiency results in significant savings in energy however, they require the use of greater areas due to the less force driving temperature and there is a more expensive capital cost to heating exchangers.

The following functions and parts are utilized when milk goes across these HTST system of pasteurization:

Float-Controlled Balance Tank (FCBT): The Float Controlled Balance Tank (FCBT) maintains an even amount of milk to feed the milk pump that is raw; it also gets any milk that is sub-temperature that is diverted through the an flow diverter valve (FDV).
Pump: A rotating positive pump that is connected to the heater and regenerator or a centrifugal pump that has a flow control mechanism to ensure that the output is constant following FCBT is utilized.
Plates: The Plate Heat Exchanger is often utilized for the HTST system, specifically to heat to temperatures that are lower than that of the milk’s boiling point. Plate heat exchangers are compact easy to clean and examined unit. The plates can be employed for cooling, heating and regeneration as well as holding. A distance of about 3 millimeters is maintained between the plates through the use of a rubber gasket that is non-absorbing or a seal.

Regeneration (Heating): The cold milk that is incoming is partially and in turn heated by hot milk that is outgoing (milk-to-milk renewal). This increases the efficiency and efficiency of HTST process as the milk coming in requires less heat from hot water to increase the temperature to hold.
Filter: Differently designed filter units that connect straight to the HTST systems are put in the pre-heater or the regeneration (heating) segment. These units, made up of 40 to 90 mesh fabric, are typically cylindrical in design. The majority of the time, two filters are used however they can be used simultaneously.
Holding: The tubes or plates assure that milk is stored for a certain amount of period of time, not more than 15 seconds and at a temperature of 720C or higher.

Flow diversion valve (FDV): The valve is used to route the milk following the heat treatment. If the milk is adequately pasteurized, the milk flows through the unit. For milk remains unpasteurized flows ahead through the unit. The milk unpasteurized milk is automatically returned to FCBT to process it. It is typically operated with the force of air against a spring that is strong.
Regeneration (cooling): The hot milk that is pasteurized is cooled in part and indirectly by the cold milk that is incoming. This further enhances the efficiency that is a result of this HTST process.
Control panel: It contains controls, instruments FDV mechanism, as well as a holding system, all inside a single moisture-proof panel.

Hot water set: circulates heated water throughout the section that heats the unit in order to keep the proper temperature of milk within extremely precise parameters.
Automatic control devices: Automated control devices include steam pressure controllers as well as control of water temp.

Steam pressure controller: Steam pressure controller keeps an unchanging hot water temperature for heating milk at the temperature required for pasteurization.

Water temperature controller: Controls the quantity of milk that leaves the tube or plate that holds the milk. This is an electronic contact instrument that can operate either an FDV or a milk pump, which prevents that milk is not leaving the storage area at the temperature that is required. The frequency and the duration of the flow divert and temperatures of milk that leaves the holding section are documented by the thermograph (recording chart) with the help of two distinct pen (De 2001).

Advantages of HTST pasteurization of milk

Large quantities of milk could be processed in a continuous manner.
Automatic precision controls assure positive pasteurization.

The equipment needs a minimal amount of floor and space for the plant.
The system can easily adapt for CIP cleaning.
The filling operation may start almost at the same time.

It is the HTST method is cost-effective because it makes use of regenerators.
The whole process is straightforward and requires only a little supervision.
The capacity can increase by increasing the amount of plates, without the need to sacrifice the floor space.

It is well-suited to the use of regenerative cooling and heating.
The closed unit reduces processing loss to a minimal.

Disadvantages of HTST system

The system isn’t adequate for handling small amounts of various milk-based liquid products.

Gaskets need to be monitored to ensure leakage is not occurring and for the proper use of sanitation.
It requires precise instruments for control.
It is impossible to drain the entire reservoir without loss.

Long-term pasteurisers could create serious bacterial issues; the plant must be thoroughly cleaned every six to eight hours in order to keep these from happening.

Tunnel (Spray) Pasteurizers for beverage

Tunnel (Spray) Pasteurizers are extensively utilized in the beverage sector to provide continuous cooling and heating of food items within sealed container. They are ideal for large volume throughput. Examples of these products include carbonated and soft beverages, juices, beers and sauces. With this technique the post-processing contamination will be greatly reduced with the primary cause being poor seams on the container. There are three primary steps within the tunnel that are heating, holding and cooling. In each of these stages, water at the correct temperature is sprayed on the container. Because the heating rate isn’t as high as those of tubes or plates and tubular heat exchangers, these methods are better suitable for longer-term or processes with lower temperatures. The average transit time can be as short as 1 h with temperatures that range between 60 to 700C for around 20 min (Brennan and Grandison 2008).

What is Batch/ Holding Pasteurization?

This process is also called the Low -Temperature-Long-Time (LTLT) method. The process has not gained much popularity for the milk industry after the HTST method was implemented. The milk and the milk products are heated or cooled in batches, either in three, two and three tank. This involves heating milk until temperatures of between 62.8 and 65.60C and maintaining it at this temperature for about 30 mins and then quickly cooling it down to less than 100C. Batch processing involves filling up the vessel with milk, heating and cooling, holding and emptying the vessel, filling into containers, as well as washing the containers (Lewis and Jun 2012).

The cooling and heating of the product are done via a wall of steel. It is heated steam or hot water. The product is then either cooled or heated, and gentle stirring is used to ensure quick heat exchange. Pasteurizers can be found in three kinds:

Water-jacketed vat: These are double-walled around the sides and bottom, in which steam or hot water in partial vacuum flows to heat and cold water is used to cool. The wall on the outside (lining) is typically lined with insulation to prevent the loss of heat. The heat exchange occurs through the wall of the lining. The temperature difference of the water used to heat it and that of the milk has to be held to an absolute minimal. The milk is stirred by gradually shifting (revolving) propellers. In the event of heating, the cover of the vat is opened to let out of flavours that are not desired; while holding the milk, the cover is shut. During the time of holding it is recommended to use an air space/foam heater (steam or electric heated) hinders the cooling of the surface of milk.
Water-spray type: A layer consisting of water is spray through an aperforated pipe onto the tank’s surface that holds the product. The product is then agitated as described previously described. A continuously moving, continuous layer of water allows for quick heat exchange.

Coil-vat type: The cooling or heating medium is pumped through a tube that is placed in vertical or horizontal position and then turned around the product. The rotating coil is causes the product to be agitated (but additional agitation might be required).

The batch pasteurizers can be inexpensive, easy to use and designed for small-scale plants and for small-volume products (De 2001).

Alkaline Phosphatase Test for Checking Efficiency of Pasteurization in Liquid Milk

Alkaline Phosphatase, a native milk enzyme. Its activity decreases at the point of pasteurization and is used as a measure of the effectiveness of pasteurization. Because milk is a known vector for several pathogenic bacteria, such as Salmonella, Compylobactor and Listeria This test has great importance for dairy producers in order to check the efficacy of heat treatment. In the method below the solution of disodium P-nitrophenyl phosphate within buffer with pH 10.2 can be used to serve as a a substrate. This colorless compound when in the solution hydrolyzed by alkaline milk phosphate to release p-nitrophenol. This in alkaline conditions imparts an intense yellow coloration of the liquid. The liberated p nitrophenol is determined directly by comparison to conventional colour discs within the Lovibond comparator. The test is not applicable to milk that is sour or preserved using chemical preservatives (FSSA 2012).

Procedure

In an empty test tube pipette five milliliters of buffer substrate, Stopper and increase it to 37oC.
Add 1 milliliter of test milk to it, shake it up and then replace the stopper.
Let it incubate at 37oC for two hours.

Incubate a blank made from boiling milk that is the exact kind like the sample being tested for each of the samples.
Take the tubes off after 2 hours and the contents should be evenly mixed.
Put the milk blank that has been boiled on the left edge of the Comparator stand and the test samples on top.

The reading is taken in reflection light by rotating this disc till the sample matches.
Note the readings that fall between two standards, by adding a minus or plus sign to the number to indicate the closest standard.

Interpretation

The test is deemed satisfactory If it shows a value of less than 10 ug of p-nitrophenyl for every ml milk. Pasteurized milk that is properly processed does not give visible hue.

Frequently Asked Questions

Q1. When was pasteurization invented?

Around 150 years ago, Louis Pasteur developed the pasteurization method while given the task of solving practical issues like keeping harmful bacteria away in various food items.

After a few decades, when the first time he came up with the idea in the 1960s, an New Jersey milk plant installed the first pasteurizer in the United States. From that point and until today with the exception of milk that’s advertised by the name of “raw” (milk that has not been pasteurized) milk, every milk sold in the United States has been pasteurized. This is just one of the many ways in which the U.S. dairy industry helps ensure that our milk is secure.

Q2. What is the process of pasteurizing milk?

In the majority of milk processing facilities the chilled milk can be heated up by passing it through the plates of stainless steel until it is at 161 degrees F. It’s kept at this temperature for a minimum of 15 seconds before being swiftly chilled back to the original temperature of 39 degrees F.

The “cool” part: One method that dairy companies save energy is to use the heat generated by heated pasteurized milk to heat the next batch of raw cold milk. The chilled milk then is used as a cooling agent for the pasteurized milk. This way the industry can use heat and refrigeration energy more effectively in the process of milk pasteurization.

Q3. Why is it necessary?

Based on the Centers for Disease Control and Prevention (CDC) the raw milk may contain harmful bacteria that be a serious health risk to yourself and the rest of your household. Pasteurization eliminates the bacteria.

Q4. Does pasteurization change milk?

No. According to CDC the pasteurization process does not alter what milk’s nutritional values are. Indeed, it is possible that you could reap all the benefits of pasteurized milk without the danger of getting sick that comes from drinking raw milk.

In terms of milk’s nutritional value and minerals, all the minerals found in milk remain the same, however there’s a slight variation in the vitamins. Raw milk has a tiny volume (<10 percentage of recommended daily allowance which is why it’s not considered to be a great supply) of Vitamin C which isn’t enough to withstand the process of pasteurization.

Additionally According to the CDC the CDC, if you’re contemplating drinking raw milk since you believe it’s a beneficial food source for beneficial bacteria such as probiotics, be aware that it’s not. It’s potentially hazardous and can cause illness. If you’re planning to have drinks or food that contain probiotics, experts like registered dietitians advise purchasing one that’s clearly labeled as probiotics, rather than trying to guess.

When you’re done with your day, you’ll be able to rest assured that the milk you drink is not only healthy for your health, but it’s safe also. All those who work in the dairy business all the way from farms to the grocery store, are aware of the importance of these qualities and strive to ensure that your family is getting the highest quality milk you can get.

Q5. How is pasteurized milk different from raw milk?

Pasteurized milk is a raw dairy that is heated at a specific temperature and length of time to kill pathogens that could be present in the milk. Pathogens are microorganisms like bacteria that can cause illness. Raw milk could contain pathogens, such as Campylobacter, E. coli O157:H7 Salmonella, Listeria and other bacteria. Raw milk is made up of milk from goats, cows, sheep and dairy animals.

The law requires that every milk sold to the public must be pasteurized before being packaged at a dairy plant that is licensed. Vitamins A and D are the only vitamins that can be added to milk. No other preservatives or additives can be added legally to milk. Vitamin A enhances your eyesight, assists you in seeing clearly when you are sleeping or in dim lighting, and assists in distinguishing the different shades. Vitamin D aids your body absorb calcium and decreases the risk of developing osteoporosis.

Q6. What are the risks of drinking raw milk?

According to an US Centre for Disease Control and Prevention study the frequency of outbreaks caused by nonpasteurized milk and products made of it was more than 150 times higher than those caused by pasteurized milk. Younger adults and children were more affected by illness. Raw milk can contain pathogens that may cause illness or disease.

Some claim to have grown as children drinking raw milk but never got sick due to it. But public health authorities have a number of instances of people getting sick due to drinking raw milk.

The requirement for the pasteurization process of milk halted large-scale outbreaks of milk-borne diseases in Canada. However, the possibility of outbreaks from raw milk continue to occur and warn us about the risks of drinking milk that is raw.

Q7. Who is at risk of getting sick?

Anyone can be sick due to pathogens found in milk that is raw.

Children, infants elderly women, pregnant women and people suffering from chronic illnesses are more susceptible to infection and are at greater chance of becoming sick due to consumption of raw milk. Children and infants are the most vulnerable because they typically drink a lot of milk.