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Pasteurization Course Summary

Vat Pasteurization of Milk

Lesson Overview

This lesson describes vat pasteurization use, equipment, and processes.

After completing this lesson, you should be able to:



One of the most effective methods of pasteurization is heating the product in a vessel in a process known as vat pasteurization.

In vat pasteurization, also referred to as batch or low-temperature long-time pasteurization, the product is heated in a jacketed stainless steel vat which has been fitted with:


Vat Pasteurization Use

Vat pasteurization is used primarily in the dairy industry as a means of preparing milk in the processing of cheese, yogurt, and other common food products.

The table below shows the required time and temperature for vat pasteurization of various food products.

Product Temperature Time
Milk 145 °F 30 minutes
Viscous products, or products with more than 10% fat or added sweetener (e.g., cream, yogurt) 150 °F 30 minutes
Egg nog, frozen dessert mixes 155 °F 30 minutes


Overview of the Vat Pasteurization Process

Vat pasteurization includes these main steps:

Note that the components of a vat pasteurizer will be presented in greater detail on the screens that follow.


Equipment Construction

In general, vat pasteurization equipment is constructed to prevent or reduce contamination. The design of the equipment should meet the following criteria:

  • Smooth, non-absorbent surfaces
  • Self-draining
  • Easily cleanable
  • Use of radiuses to avoid corners
  • Proper slope to ensure self-drainage
  • Raised edges to prevent potential contaminant from flowing back into equipment
  • Overlapping drip deflectors on inserted implements


Inlet Line

Product components (e.g., dairy products, liquid sugar and sweeteners, water, stabilizers, vitamins) are added to the vat through the inlet line. The inlet line is designed to:

Note that certain flavoring ingredients (e.g., dry sugars, fruits and roasted nuts, and safe and suitable bacterial culture organisms) may be added to the product after pasteurization.



Covers of vat pasteurizers are constructed to prevent the entrance of surface contamination or foreign material.

Cover edges must be designed with overlapping “shoe box” style lids. This design prevents contaminates from entering when the cover is raised, and drains away splashes and drips to the outside of the vat pasteurizer.



The vat pasteurizer jacket is a double-walled covering. In the space between the walls, circulating water, steam, or heating coils of water and steam heat the product in the vat.

The product should be heated in as short a time as practicable, and in no case should this exceed 4 hours.



All vats must be equipped with mechanical means of agitation.

An agitator is designed to keep milk or milk product moving at all times by running constantly during the pasteurization cycle. This results in uniform product and temperature throughout the vat.

The most efficient agitators push the product down and sweep it against the heat exchange surface on the sides and bottom of the vat.

Agitator shafts must be fitted with effective drip deflection shields to prevent contamination of the product. They must also be easily cleanable.


Indicating Thermometers

The indicating thermometer is the “official” thermometer.

Indicating thermometers:


Air Space Thermometers

Air space thermometers measure the temperature of the air space above the product in the vat. These thermometers:

The air space thermometer bulb must be positioned 2 to 3.5 inches from the bottom of the cover, and at least 1 inch from the top surface of the product during pasteurization.

Note that the air space thermometer is the smaller thermometer in the image shown.


Recording Thermometers

The recording thermometer provides a record of the pasteurization cycle and heat treatment, including the holding time.

Recording thermometers:


Recording Thermometer Chart

The recording thermometer chart must be graduated in time increments of not more than 10 minutes for a maximum record of 12 hours.

In addition, the recording thermometer chart should include:


Air Space Heaters

The air space above the product in the vat must be maintained at least 5 °F higher than the minimum pasteurization temperature for the product being pasteurized.

An air space heater, typically an electric boiler with steam traps and filters to produce culinary steam (i.e., steam that has been properly filtered for use in food processing), may be necessary to maintain these minimum air space temperatures.

These heaters must:

  • Be properly installed.
  • Be easily cleaned.



The inlet and outlet valves of the vat pasteurizer are normally constructed of solid stainless steel to:

The valve plug is also stainless steel, allowing for thorough heat penetration to ensure that any milk that weeps into the area between the plug and the valve body gets full heat treatment.

Non-stainless steel plugs (e.g., rubber or plastic) must not be used, as any milk that may have made its way around the sides of the plug will not be adequately heated.

Valve bodies or valve plugs include leak detection grooves, which are designed to prevent leakage of raw milk past the valve body. These grooves are curved or placed at such an angle to allow proper draining, and must remain fully open and free from obstruction during pasteurization.

Any milk that is trapped inside the valve plug when the valve is shut will then be drained via the leak detection grooves.


Holding Periods

Remember that vats are operated so that every particle of product is heated for at least 30 minutes and no more than 4 hours at or above the required minimum temperature for that product.

To ensure that these requirements are reached, it is important that the operator:

In the event of any mechanical failure of any kind (e.g., a lifted cover or an agitator malfunction), the holding period must be restarted.


Critical Control Points

There are various steps in food processing at which control measures can be applied to prevent, eliminate, or reduce a food safety hazard to an acceptable level.

When conducting an inspection of a vat pasteurizer, it is essential to focus on these critical control points. Critical control points are those points in processing where a preventive measure occurs at the last opportunity in processing for eliminating a hazard.


Critical Control Points for Vat Pasteurization

To determine whether any of the critical control points of vat pasteurization failed, ask yourself:


Lesson Review

You have completed the Vat Pasteurization of Milk lesson. You should now be able to:

The next lesson will discuss high-temperature short-time (HTST) pasteurization of milk.


HTST Pasteurization of Milk

Lesson Overview

This lesson describes high-temperature short-time (HTST) pasteurization use, equipment, and processes.

After completing this lesson, you should be able to:



In high-temperature short-time (HTST) pasteurization, the product is heated to the minimum temperature and held continuously at or above that temperature for at least the minimum time required.

Compared to vat pasteurization, the required temperatures are much higher and the holding periods much shorter.


HTST Pasteurization Use

Below is a table showing the required time and temperature for HTST pasteurization of various milk products.

Product Temperature Time
Milk 161 °F 15 seconds
Viscous products, or products with more than 10% fat or added sweetener (e.g., cream, yogurt) 166 °F 15 seconds
Egg nog, frozen dessert mixes 175 °F 25 seconds


Overview of HTST Pasteurization

HTST pasteurization includes these main steps:

  1. Product enters the constant level tank and is drawn under reduced pressure to the regenerator section.
  2. In the regenerator section, the product is pre-warmed by hot product flowing through regenerator plates.
  3. The product is then drawn through the timing pump to the heater section.
  4. The now-hot product flows through the holding tube.
  5. The product contacts the indicating thermometer and the recording thermometer.
  6. If it has not reached the minimum required temperature, it is returned back to the constant level tank via the diversion port.
  7. If the product is at or above the minimum required temperature, it passes through the regenerator plates (on the pasteurized side) and then to the cooling section.
  8. The product exits the cooling section and rises to an elevation of at least 12 inches above any raw product.
  9. Finally, the product passes to a storage tank for packaging.

The next screens address the components of the HTST system in greater detail.


Constant Level Tank

The constant level tank (or balance tank) provides:

The constant level tank must have a sanitary design, and the overflow level must be at least 1 inch below the lowest level of raw milk in the regenerator.



The regenerator section:


Timing Pump

The timing pump:

The timing pump must be set so the maximum delivery rate is equal to or less than the calculated maximum flow rate. This ensures that the desired minimum holding time is obtained.

Common types of timing pumps include:


Thermal Exchange Systems

While there are different types of thermal exchange systems used in HTST pasteurization, they all function to:

The two types of thermal exchange systems are:

Both types use indirect heating methods, which involve transferring heat from the heat medium through a partition into the product.

Indirect Heating Methods

Below are the advantages and disadvantages of indirect heating methods.




Plate Heat Exchanger

The PHE uses metal plates to transfer heat from pasteurized product to raw product. These plates are pressed with surface patterns to create and increase turbulence in the product stream and enhance the heat transfer.

Molded gaskets around the plate edges and ports prevent leakage and intermixing of fluid. The raw side deflector plates are drilled with weep holes that will allow the regenerator to be free-draining during a shutdown.


Tubular Heat Exchanger

Unlike PHEs, THEs have no contact points in the product channel. THEs may have either a double-tube or triple-tube design. However, from the standpoint of heat transfer, the THE is less efficient than the PHE.

The tubes within a THE have spiral or corrugated surfaces to increase turbulence and heat exchange.


Holding Tube

The holding tube ensures that the product is at sterilization temperature for the proper time, and that temperature variation does not exceed 1 °F.

The holding tube:

The length of time the product spends in the holding tube is determined by the pumping rate of the timing pump, the length of the holding tube, and the product surface friction. After flowing through the holding tube, the product contacts the indicating thermometer and the recording thermometer.

The holding tube must:


Indicating Thermometer

The indicating thermometer in a HTST pasteurizer shows the accurate, “official” temperature of the product.

The indicating thermometer should:


Recorder Controller

The recording controller/safety thermal limit recorder (STLR) automatically:

The recording thermometer must be located within 18 inches of and upstream from the flow diversion device.

STLRs may be one of the following two types:


Flow Diversion Device

The purpose of the flow diversion device is to safely and accurately control and separate raw and pasteurized product flow.

In order to do this, the flow diversion device:

Flow diversion devices may be one of the following two types:


Cooler Section

In the cooler section, the product is chilled down to a preset temperature (below 45 °F) by glycol or ice water solutions.

When the product exits the cooler section, it rises to an elevation of at least 12 inches above any raw product. Finally, the product passes to a storage tank or vat to await packaging.


Vacuum Breakers

Vacuum breakers:


Critical Control Points for HTST Pasteurization

As with vat pasteurization, it is essential to focus on the critical control points when conducting an inspection of a HTST pasteurizer.

The table below lists some key areas to inspect and considerations for those areas.

Component Considerations
  • Is the pasteurized milk discharged from the regenerator properly?
  • Will the raw milk drain freely back from the raw side of the milk-to-milk regenerator when all flow-promoting devices are stopped?
Timing Pump
  • If the system has a timing pump, is the homogenizer equipped with a recirculation loop?
Holding Tube
  • Is the holding tube less than 7 inches in diameter, with permanent supports and no alterable sections?
  • Does the tube slope continuously uphill at not less than 0.25 inch per foot from start to finish?
  • Is the indicator thermometer bulb as close as possible to the recorder bulb?
  • Is the recording thermometer bulb within 18 inches of the flow diversion device?
  • Are the recording thermometer charts properly maintained?
Vacuum Breaker
  • Are the required vacuum breakers located in the proper place?
  • Are they functioning?


Lesson Review

You have completed the HTST Pasteurization of Milk lesson. You should now be able to:

The next lesson will discuss the pasteurization of juice.


Pasteurization of Juice

Lesson Overview

This lesson describes key points about the pasteurization of juice.

After completing this lesson, you should be able to:



Pasteurization of juice, like pasteurization of milk and other dairy products, is used to kill any contaminating pathogens that might be contained in the raw juice. The time requirements for juice products depend on the target pathogens, typically the protozoan parasite Cryptosporidium in fresh apple juice and bacterial pathogens in citrus and non-apple juices.

Below are the time and temperature requirements for thermal heat treatment of juice to achieve the 5-log reduction performance standard:


Vat Method

In the vat or batch method of pasteurizing juice:

With this pasteurization method, both the time and temperature of the juice treatment must be monitored to ensure that the process is achieving the 5-log pathogen reduction.

The vat method of juice pasteurization is often used by small juice operators. However, as with any method of pasteurization, the vat method requires proper mixing and temperature monitoring.


Vat Method: Carrot Juice Example

In June, 2012, a juice company recalled all of their vat-pasteurized carrot juice due to a Clostridium botulinum hazard.

C. botulinum can survive high temperatures and thrives in oxygen-free environments. It is most commonly found in low-acid foods such as carrot juice.

The recalled carrot juice was processed at the correct time and temperature in a vat pasteurizer, but after pasteurization, entire 55-gallon drums of hot carrot juice were placed in a refrigerator for an unknown cool-down time.


HTST Method

With the HTST or continuous method of pasteurizing juice, large amounts of product can be heated and cooled quickly.

The process is similar to that used for milk and milk products:


HTST Pasteurization of Juice: Differences

While the process used for HTST pasteurization of juice is very similar to that for milk, there are a few differences.

For example, the two types of heat exchangers presented in the previous lesson are used for different types of juice:

Also, the required holding time for HTST pasteurization of juice (3 to 6 seconds) is much shorter than the holding time for HTST pasteurization of milk (15 seconds).


Critical Control Points

As with the pasteurization of milk, there are key critical control points to focus on when conducting inspection of a vat or HTST pasteurizer of juice.

Key questions to ask for either system include:

Key questions to ask for HTST systems include:


Lesson Review

You have completed the Pasteurization of Juice lesson. You should now be able to:

The next lesson will discuss the pasteurization of other products.


Pasteurization of Other Products

Lesson Overview

This lesson describes key points about the pasteurization of other products.

After completing this lesson, you should be able to:



Pasteurization is most often associated with milk and juice.

However, there are many other products that are pasteurized in order to kill harmful foodborne organisms, including:


Pasteurization of Whole Eggs

Egg pasteurization uses a water bath and motion to ensure that whole eggs are pasteurized without cooking the eggs.

Egg whites coagulate at 140 °F. Therefore, heating an egg above 140 °F would cook the egg, so processors pasteurize the egg in the shell at 130 °F for 45 minutes.

This new process is being used by some manufacturers, but it is not yet widely available.


Pasteurization of Egg Products

The term “egg product” may refer to dried, frozen, or liquid eggs, with or without added ingredients.

Regulations currently provide pasteurization times and temperatures for:


Pasteurization of Shellfish

Examples of pasteurized fishery products include pasteurized crabmeat, surimi-based analog products, and lobster meat.

Pasteurization is usually performed on fishery products after the product is placed in the hermetically sealed finished product container. For example, blue crab is pasteurized by placing containers of blue crab into a hot water bath tank for a minimum time and temperature, and then cooling them in ice water.

This pasteurization process may put such products at risk for recontamination after pasteurization from defective containers or contaminated cooling water. Therefore, certain controls (e.g., ensuring container seal integrity) are critical to ensuring food safety.


Pasteurization of Shellfish

The minimum time and temperature required to properly pasteurize two shellfish products are shown in the table below.

Product Temperature Time
Blue crabmeat 185 °F 31 minutes
Surimi-based products 194 °F 10 minutes


Pasteurization of Shellfish: Pathogens

Pasteurization of shellfish reduces:


Pasteurization of Shellfish: Crabmeat Example

An example of pasteurized shellfish is crabmeat.

Crabmeat is processed in different ways: fresh, pasteurized, and shelf stable. Traditionally, live crabs are cooked, and then the meat is hand-picked and packed in containers for market under refrigeration and sold as fresh crabmeat. The crabmeat may also undergo further heat treatment and be sold as a pasteurized product with an extended shelf life (6-18 months). Canned, commercially sterile product is also available.

Crab pasteurization was initially a means of extending the shelf life of this perishable product, and no target spoilage organisms or pathogens were identified. However, concerns about the presence of type E C. botulinum led to an increase of required times and temperatures for pasteurization.


Pasteurization of Shellfish: Oyster Example

Another example of pasteurized shellfish is oysters.

High pressurization processing, a techniques used in the meat and juice industries, was adapted for processing oysters in 1999. In this process, oysters are cleaned, washed, sorted and graded. They are then banded and placed in a stainless steel cylinder in preparation for the high-hydrostatic pressure of 45,000 pounds per square inch. After pressurization, the oysters are then shucked for half shell or packaged as banded oysters.


Pasteurization of Shellfish: Critical Control Points

The critical control points for pasteurization of shellfish may include:


Lesson Review

You have completed the Pasteurization of Other Products lesson. You should now be able to: