This document provides a comprehensive overview of food preservation through pasteurization, particularly focusing on milk. It details the steps involved in pasteurization, different methods (including vat, HTST, and UHT), advantages and disadvantages, and the importance of maintaining temperature control throughout the process. The document emphasizes the need for proper agitation and heating balance to ensure effective pasteurization and safety in milk production.

1. FOOD PRESERVATION BY
PASTEURIZATION
BY
ASSIT. PROF. Dr. P. BERCIYAL GOLDA

2. CONTENTS
Introduction
History
Purpose
Foods used for Pasteurization
Steps in Pasteurization
Process Flow Diagram Pasteurization Milk
Milk Pasteurization
Methods of Pasteurization
Advantages
Disadvantages

3. INTRODUCTION

16. Steps of Pasteurization
1. Milkchilling
 Chilling is not a pasteurization process but it is a necessary
step when dealing with large volumes of milk.
Milk leaves the cow’s udder at temperatures above the ambient, which
encourages rapid bacterial multiplication that speeds up spoilage.
 However, reducing the temperatures to between 2° C to 5°
C arrests bacterial growth and metabolism.
This provides a head start at keeping the quality before proper
pasteurization commences.

17. 2. Pre-heating(regeneration)andStandardizationStage
After bulking, the chilled milk is heated to about 40°C to facilitate
easy separation of butterfat during standardization.
The system uses regenerative heating, i.e., it uses the heat of the
already pasteurized milk to heat up the incoming chilled milk. The
chilled milk, in a counter current flow, cools down the pasteurized
milk.
The purpose of standardization is to obtain a product with uniform
content of butter fat

18. 3. Clarificationstage
 Clarification is essential for removing all foreign matter from
the product.
Large solid particles are removed by straining the milk through
tubular metallic filters.
 A centrifugal clarifier (not the one used for standardization)
is used to remove all soil and sediments from milk.
 The filters, usually fitted in parallel twins permits continuous
processing as one can be cleaned while the other is running.
 Clean the filters regularly (between 2 to 10 operational hours
depending on the level dirt) to avoid growth of bacteria.

19. 4. Standardizationstage
 It is important to standardize milk fat to ensure that you end up
with a product of consistent quality in the market. Different consumers
prefer different products. There are customers who will consume skim milk
only while there are those who will take low fat milk. There are those who
will take standardized milk while there are those who prefer high
fat milk.
 Standardization is necessary to ensure that all the customers
are catered for. Again, it is during the process of standardization
that you get to separate the butterfat that is used for making cream
and other fat based products such as butter and ghee.

20. 5. Homogenization stage
 Homogenization is a physical process of breaking down the the
milk fat globules into tiny droplets to discourage cream separation.
 Tiny droplets of fat do not rise in a milk column since reducing
their sizes also increases their density in the milk.
 A milk homogenizer working at between 100 to 170 bars splits
all the fat globules into very tiny droplets that increases the level of
integration of the fat in the milk.
As a result, the milk fat remains uniformly distributed in the milk.

21. 6. Heatingsection
 Utilizes heat from steam to raise the temperatures of the
milk from about 60°C to the required 72°C that is effective to kill
the Clostridium botulinum spores.
 The steam exchanges heat with the milk across the PHE
plates in a counter current motion.
 At the end if this section, there is a temperature sensor,
which controls the flow diversion valve.
 Any milk that does not attain the required temperature is
diverted back to the heating section until it attains the required
temperatures.

22. 7. Holding section
 After heating, milk flows into the holding tubes whose lengths have
been calibrated with the milk flow rate to ensure that milk takes at least 16
seconds in the tubes. All the milk must maintain the required pasteurization
temperatures at the end of the tubes.
 In case of a breach, a sensor will trigger the flow diversion valve to
take the milk back to the heating section to bring the milk to the required
temperature. Once the milk has attained the required temperatures at the
end of the holding tubes, milk flows back to the regeneration section to heat
the incoming chilled milk while in itself being cooled down to about 30°C.

23. 8. Cooling/chillingsection
 After regenerative cooling of pasteurized milk, it moves to
the cooling section of the PHE where chilled water/PHE coolant
lowers the temperature of pasteurized milk to 4°C.
 The chilled milk is then pumped to the packaging machines for
aseptic packaging and subsequent storage in the cold room.

25. Milkpasteurization
 Milk pasteurization is the process of heating milk (or milk
product) to a predetermined temperature for a specified period without
re-contamination during the entire process.
 The predetermined temperature usually depends on the heat
resistance of spoilage microorganism that the pasteurization program is
targeting to destroy

29. o Vat pasteurization, also known as batch pasteurization or
the holding method, heats every particle of milk or cream in
properly designed and operated equipment, at 145°F (63°C) for
30 minutes*. If the fat content of the milk product is 10
percent or greater, or a total solids of 18% or greater, or if it
contains added sweeteners, the specified temperature shall be
increased by 5°F (3°C). Vat pasteurization helps destroy all
disease-producing bacteria, as well as 90-99 percent of all other
bacteria that may affect product quality. Because of this,
pasteurization is the most important function of a milk plant.
o In vat pasteurization, it is necessary to heat the milk
product to 145°F in the vat. The presence of both butter
granules and cream plug are possible in milk and cream. Agitation
is necessary to achieve the proper consistency and texture as
well as rapid, even heating. Incorrect agitation will cause
churning.

30. Operating a Vat Pasteurizer
 Finding the right balance of heating and agitation is
important to efficiently operate vat pasteurization equipment. If
the heating temperatures are too low, the milk product
temperature will not raise quick enough. If heating temperatures
are too high, the milk product may “cook on” the heating surface.
The speed of heating is affected by the ability of your agitator
to keep the product moving to, and away from, the heating
surface.
However, simply speeding up your agitator will not necessarily
give you the desired result.
Agitators are designed for certain speeds and highly efficient
agitators may require high heating water temperatures.
Failure to balance the heating surface with your agitation type
and speed can result in improper pasteurization.

31.  During the holding period, the vat must remain closed to
prevent cooling from occurring during pasteurization. Proper vat
pasteurization equipment should have an airspace heater to keep
the air above the product at or above 145°F.
 Airspace heaters also ensure the pasteurization of milk
droplets that are splashed on the sides of the vat and condensate
on the inside of the vat cover.
 The bottom and sides of the vat must be insulated or
jacketed to maintain proper temperatures during the holding
period.

32. High-Temperature Short-Time (HTST) Pasteurization
HTST pasteurization uses stainless steel heat exchange
plates where product flows on one side while the heating media
flows on the opposite side to raise milk temperatures to at least
161° F (72° C) for at least 15 seconds*, followed by rapid cooling.
This was first developed by A.P.V. Co. in the United Kingdom in
1922. It is the modern method of pasteurizing milk and is
invariably used where large volumes of milk are handled.
The HTST pasteurizer gives a continuous flow of milk
which is heated to 72°C for 15s and then promptly cooled to 5°C
or below.
Flash pasteurization, also called "high-temperature short-
time" processing, is a method of heat pasteurization of perishable
beverages like fruit and vegetable juices, beer, kosher wine, and
some dairy products such as milk.

34. Why is HTST Pasteurization the Preferred Method?
High temperature short time pasteurization is a
continuous process that efficiently and effectively destroys
microorganisms in milk products. An HTST pasteurization system
is a modular unit that includes a plate-and-frame heat
exchanger, stainless steel balance tank, pumps, holding tube,
valves piping and controls. Vat pasteurization, or the holding
method, is the oldest method for pasteurizing food products.
However, over the years HTST has gained favor in the
food industry for multiple reasons:
Large equipment capacity allows large volumes at one time
Continuous process allows for bottling to begin when
pasteurization begins
Highly energy efficient
Minimal chance of damage to milk product
Fully utilized regeneration
Equipment is easy to clean and sterilize
Thermophiles are less troublesome

37. Low-temperaturelong-time(LTLT)/Batchpasteurization
 Milk is heated, held and cooled in the inner vessel. The
space between vessel and the outer casing forms a jacket,
through which the heating or cooling medium is circulated.
 To heat the milk, hot water or low-pressure steam is
circulated through the jacket and milk is continuously agitated for
rapid and uniform heating. The heating process could be manually
or automatically controlled. The milk is heated to a minimum of
62.7°C and held at this temperature for minimum 30 min. It is
then cooled as rapidly as possible to 4°C.
 A cooling medium is circulated in the jacket for chilling
the milk, but more often the heated milk is discharged to a
surface cooler where a film of milk flows down the corrugated
metal plates or series of interlocked tubes. A cooling medium such
as brine or chilled water is circulated on the other side of the
plates or through the tubes.

40.  This is a completely closed pasteurization method. The
product is never exposed even for a fraction of a second during the
entire process.
It involves heating milk or cream to between 135°C to 150°C for one
to two seconds, then chilling it immediately and aseptically packaging
it in a hermetic (air-tight) container for storage.

41. Despite the risk of Millard browning, UHT pasteurization remains
the most popular milk preservation method for safe and stable milk.
(UHT) pasteurization involves heating milk or cream to 138°to 150°
C (280° to 302° F) for one or two seconds. Packaged in sterile,
hermetically sealed containers, UHT milk may be stored without
refrigeration for months.
Ultra high temperature pasteurization, sometimes referred to as
HST pasteurization or ultra-pasteurization, is a process in which
milk or other dairy products are heated to 280 degrees Fahrenheit
for a brief time—just two seconds—and then quickly cooled back
down.

42. ULTRA STEAM IRRADIATION

46. 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 milk is pasteurized
5. Easily cleaned and sanitized (system adapts itself to CIP)
6. Lower operating cost (due to regeneration system)
7. Reduced milk losses
8. Development of thermophiles is not a problem
9. Automatic precision controls ensure proper pasteurization.

47. Disadvantages
1. The system is not well-adapted to handling small quantities of
liquid milk products
2. Gaskets require constant attention for possible damage and lack of
sanitation
3. Complete drainage is not possible (without losses exceeding those
from the holder system)
4. Margin of safety in product sanitary control are so narrow that
automatic control precision instruments are required in its operation
5. Lethal effect on high-thermoduric bacteria in raw milk is not as
great as compared to LTLT system
6. Accumulation of milk-stone in the heating section.