Processing of Milk
UNIT 5 PASTEURIZATION
Structure
5.0 Objectives
5.1 Introduction
5.2 Definition and purpose of pasteurization
Time-temperature combination
Purpose
5.3 Theory of pasteurization
Limiting factors for heat treatment
Types of heat treatment
5.4 Batch Pasteurizer
5.5 HTST Pasteurizer Plant and its components
Flow diagram of pasteurization process
Components of a HTST pasteurization plant
Plate heat exchanger
Instrumentation
5.6 Operation of pasteurization plant
Starting the plant
Shut down of the plant
Cleaning and Sterilization of the plant
Pasteurization of milk
Trouble shooting
Preventive maintenance
5.7 Test for Pasteurization Efficiency
5.8 Let Us Sum Up
5.9 Key Words
5.10 Some useful Books
5.11 Answers to Check Your Progress
5.0 OBJECTIVES
After studying this unit, we should be able to:
define and give the reasons for pasteurizing the milk
explain the theory of pasteurization
list important parts of a pasteurizer
describe the procedure of operating a pasteurizer.
5.1 INTRODUCTION
Pasteurization is a key process in modern dairy plant operations and forms an
integral part of manufacturing of various indigenous and western dairy products.
Milk is a perfect medium for growth of micro-organisms, and growth of pathogenic
organisms can cause diseases such as tuberculosis and typhus. Pasteurization kills
the organisms responsible for spread of diseases through milk and makes it safe for
consumption.
The word pasteurization has been named after an eminent French scientist, Louis
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Pasteur. In general terms it is heating milk or its products to such temperature, Pasteurization
which destroys nearly all the microorganisms, present in it without affecting the
composition or properties of the product. Thus it is important to monitor the
pasteurization process as improperly/under pasteurized milk can cause the infection.
This unit will give us working knowledge of pasteurization process. Let us understand
the process.
5.2 DEFINITION AND PURPOSE OF PASTEURIZATION
Fresh milk produced from healthy milch animals generally contains minimum load
of microorganisms. In the course of handling at the farm, milk is liable to be
contaminated by various microorganisms mainly bacteria. Rapid chilling to below
4C temperature slows down the growth of microorganisms in the milk. Milk must
be treated by an established process so that all pathogenic microorganisms are
killed before it is consumed as fluid milk. This is achieved by heat treatment.
Pasteurization is one of the most important heat treatment processes. The term as
applied to market milk refers to the process of heating every particle of milk to a
temperature of at least 63C (145.4F) for 30 minutes or 71.7C (161F) for 15
seconds (or to the temp-time combination which is equally efficient) in properly
designed equipment. Milk is immediately cooled to 4C and stored in cold storage
maintained at 4+1C.
As per definition of International Dairy Federation (IDF) Pasteurization is a process
applied to a product with an objective of minimizing possible health hazard arising
from pathogenic microorganisms associated with milk by heat treatment, which is
consistent with minimal chemical, physical and organoleptic changes in the product
The heat treatments suggested by the IDF for the pasteurization of milk are 15
seconds at 71.7C=161F or 30 minutes at 62.8C=145F can be regarded as
universal reference treatments. Three aspects emerging from the definition are:
(i) level and degree of heat treatment, (ii) minimum chemical, physical and organoleptic
changes, and (iii) minimum health hazards. These are elaborated here.
i. Time-Temperature Combination
The time-temperature combinations normally used for pasteurization of fluid milk
are as follows:
63C (145.4F) and held at that temperature for at least 30 minutes
72C (161.6F) and held at that temperature for at least 15 seconds.
The milk is then immediately cooled to a temperature not greater than 4C. The
selected heat treatment shall be applied only once. This means pasteurization includes
heating to a specific time-temperature combination followed by immediate cooling
to 4C.
ii. Purpose
Milk is pasteurized for two purposes:
To make safe for human consumption by destroying pathogenic microorganisms
present in milk.
To improve its keeping quality.
The most heat resistant pathogenic organism at pasteurization temperature is the
Mycobacterium tuberculosis and hence this has been made as an index organism
to achieve complete safety of milk. Any heat treatment, which will destroy this
organism, can be relied upon to destroy all other pathogenic organisms as well as
other organisms involved in milk spoilage. Some bacteria, call thermodurics (heat
resisting) may survive during pasteurization but immediately cooling slows down
their growth and thus prevents them causing spoilage such as flavour taint or 25
Processing of Milk souring. Although, the main purpose of heat treatment is to destroy all microorganisms
capable of causing disease in humans but pasteurization has two additional benefits,
i.e. the destruction of a large number of spoilage microorganisms present in raw
milk and deactivation of some natural enzymes like lipases, which can adversely
affect the quality of manufactured products, i.e. lipolysis or breakdown of fat into
glycerol and free fatty acid. However, we must be clear that pasteurization is not
a substitute for cleanliness during milk production. The pasteurization process should
only be applied to raw milk obtained from healthy cow, which is clean, sweet and
has a low bacterial count.
Check Your Progress 1
1. Give two reasons for pasteurizing the milk.
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2. Describe the time-temperature combination normally used for milk pasteurization.
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5.3 THEORY OF PASTEURIZATION
We have understood that heating milk to selected time-temperature combination
effectuates pasteurization to ensure destruction of all pathogenic microorganisms.
Theoretically, aspect of pasteurization is the heat treatment applied to the milk to
destroy pathogenic organisms. The process parameters of heat treatment or time-
temperature combinations are elaborated below: (a) Limiting factors for heat
treatment and (b) Types of heat treatment.
i. Limiting Factors for Heat Treatment
The upper and lower limits of temperature to pasteurization process are based on
thermal death point of tubercle bacilli and beginning of reduction of the cream line.
The thermal death time for tubercle bacilli provides the lower limit to heat treatment.
The adverse effects on the commercial quality milk provide an upper limit for the
possible time- temperature combinations used in pasteurization. As the cream line
is the first quality to be affected, it is generally used as the standard indicator of
changes in the chemical, biological and physical properties of milk caused by over
heating.
In the early 1920s, North and Park performed extensive tests by heating milk
samples containing tubercle bacilli at different time-temperature combinations that
destroyed all the tubercle bacilli present in them. The time-temperature combinations
that destroy all tubercle bacilli are taken as thermal death points. Table 5.1 shows
a number of thermal death points for tubercle bacilli.
Table 5.1: Thermal Death Points for Tubercle Bacilli
Temperature Time
C F
100.0 212 10 seconds
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93.3 200 20 seconds Pasteurization
82.2 180 20 seconds
76.7 170 20 seconds
71.1 160 20 seconds
68.2 155 30 seconds
65.6 150 2 minutes
62.8 145 6 minutes
61.1 142 10 minutes
60.0 140 10 minutes
57.8 136 30 minutes
55.6 132 60 minutes
These thermal death points can also be plotted on a graph to give a thermal death
line.
Safety margin: This is the additional amount of heat treatment (time and temperature
above the thermal death point of the tubercle bacillus) so that, under no circumstances,
will any tubercle bacilli be left alive after correct routine operation of a pasteurizer.
Certainly, a more intense heat treatment would obtain more efficient antibacterial
results than pasteurization. On the other hand, the milk is not inert to heating; over-
heating adversely affects the appearance, taste, nutritional and technological value
of milk. Combination of higher temperature and longer holding time-temperature are
also recommended for HTST pasteurization of dairy products having higher contents
of solids.
ii. Types of Heat Treatment
The heat treatment given in form of (i) holding and (ii) continuous correspondingly
relate with two methods of pasteurization i.e.
Batch, holding or Low Temperature Long Time (LTLT) method and
Continuous, High Temperature Short Time (HTST) method.
In the batch method, the milk is heated to 63C in a tank or vat equipped with a
hot water or steam jacket and agitators to keep the milk agitated; held for 30
minutes and then partly cooled in the batch pasteurizer. The further cooling is done
by surface/plate cooler. This method is mostly used for processing of around 5000
liters of milk.
High Temperature-Short Time (HTST) pasteurization is the process, which is
commonly used now a day all over the world. Plate Heat Exchanger (PHE) is used
to heat, hold and cool the milk. Milk is heated to a temperature of at least 72C
and held at that temperature for not less than 15 seconds and then immediately
cooled to a temperature not greater than 4C.
Check Your Progress 2
1. What are the different methods of pasteurization?
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Processing of Milk 2. Enumerate the temperaturetime combination for the two methods of
pasteurization.
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5.4 BATCH PASTEURIZER
The parts of a typical batch pasteurizer are following:
Insulated outer casing
Insulated hinged cover
Stainless steel inner vessel
Agitator and its motor
Outlet cock and heating water distribution pipe.
a. Insulated outer casing
b. Insulated hinged cover
c. Stainless steel inner vessel
d. Agitator
e. Agitator motor
f. Outlet cock
g. Heating water distribution pipe
c g
Figure 5.1: Batch Pasteurizer
This system is well suited for small-scale operation, where less than 3000 to 5000
litres of milk are available. The vat may be rectangular, but a vertical, cylindrical
design is preferred for practical reasons. The vat normally consists of an inner
vessel, surrounded by an insulated outer casting, thus forming a jacket, through
which hot water or steam is passed (Figure 5.1). After the milk has reached the
required temperature (63.0C), it is usually held at that temperature for a certain
fixed period (30 minutes). Thereafter, it is cooled as quickly as possible either by
circulating refrigerant/chilled water or through plate/surface chiller. Cooling the milk
after pasteurization by circulating a refrigerant in most cases cold water
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through the jacket or the vat may take much time. Therefore, a separate small- Pasteurization
capacity surface, tubular or plate cooler may be used to rapidly cool the milk to the
required temperature. This system also has the advantage that the vat will be
available sooner for the pasteurization of another batch of milk.
Batch pasteurizers have a small heating surface area relative to their contents.
Heat transfer is greatly improved by agitating the milk. Agitators of different design
are used for this purpose. They may even consist of double-walled paddles or other
devices with internal steam or water circulation. Care must be taken to avoid foam
formation during filling of vat. It is very difficult to heat the milk and foam together
uniformly and consequently microorganisms present in the foam may survive
pasteurization. If the inlet valve is at the bottom of the vat, foam formation can
easily be prevented. A lid or cover on top of the vat promotes a uniform temperature
of the contents and prevents skin formation on the milk.
5.5 HTST PASTEURIZER PLANT AND ITS
COMPONENTS
The HTST system is the most common method used by the dairy plants for
pasteurization of milk. The main advantage of HTST pasteurization is its capacity
to heat treat milk quickly and adequately with built-in safeguards that prevent
improper pasteurization due to under heating of milk. The HTST system employs
plate heat exchangers for heating, regeneration and cooling. The system consists
of feed pump, plate heat exchanger, holding section, flow diversion valve,
instrumentation, essential services and piping system. The entire process is automatic
and is ideal for handling of 5000 litres per hour (lph) or higher quantity of milk. This
is a continuous flow process and also saves energy due to regeneration section
(Figure 5.2). In order to understand a pasteurizer let us go systematically for:
Figure 5.2: Flow diagram of high temperature short time pasteurizer (H.T.S.T.) 29
Processing of Milk Flow diagram of process;
Different compartments/sections;
Plate heat exchanger, which is the main part; and
Instrumentation
i. Flow diagram of pasteurization process
The schematic flow diagram of HTST pasteurization is given in Figure 5.3.
Raw milk enters the constant heat tank (balance tank), passes to the milk pump
and then through a flow controller to the plate heat exchanger. The plate heat
exchanger consists of regeneration section, heating, holding and cooling sections.
30 Figure 5.3: Flow Diagram of Pasteurization
The raw milk enters the pre-heating (regeneration section), where hot pasteurized Pasteurization
milk (72C) flows counter current to the raw cold milk, within adjacent plates,
transferring heat for pre-heating of raw milk and pre-cooling of pasteurizing milk
resulting in energy saving. The partially heated raw milk passes through a filter or
clarifier and homogenizer. It then enters the heating section where it is heated to
at least 72C. The hot milk then passes through the holding section to ensure that
the fastest moving particles of milk are held at 72C for at least 15 seconds.
The flow diversion valve diverts the milk to constant head tank if it is not properly
heated to pasteurization temperature. Properly pasteurized milk passes forward
through the flow diversion valve into the regeneration section where it is cooled by
incoming cold raw milk passing in the opposite direction on the other side of the
plates. Milk enters the cooling section and is cooled at 4C before storage.
An indicating thermometer situated at the outlet of the holding section measures the
temperature of the hot milk and this is recorded on a revolving thermograph. If the
temperature of the milk falls below 72C, the hot milk-recording pen drops past the
set pointer on the thermograph and this activates the flow diversion value, the safe-
guard pen and an alarm bell. The flow diversion valve diverts the unheated milk into
the constant head tank for re-circulation until the milk reaches the correcting temperature.
ii. Components of a HTST Pasteurization Plant
The complete pasteurizer plant consist of:
Constant head tank
Milk feed pump
Flow controller
Filters
Clarifier
Homogenizer
Plate heat exchanger consisting of bank of plates compartmentalized into
regeneration, heating, holding and cooling sections,
Flow diversion valve
Instruments associated with indicating controlling and/or recorded functions,
Systems for providing steam, air, water, heating and cooling arrangements, and
Piping system to link various components
iii. Plate Heat Exchanger (PHE)
The Plate Heat Exchanger consists of a bank of plates inter-connected (sections)
held in a rigid frame (figure 5.4). The main function of the PHE is the exchange
or transfer of heat from a hot liquid (hot water or hot pasteurized milk) to a cooler
one (cold water, chilled water brine or raw milk) across a metal plate. Let us see
how the heat is transferred through plates.
Plates: The plates are thin stainless steel sheets usually rectangular in shape. The
plates are corrugated and cause a turbulent flow, which increases rate of heat
exchange. The rate of heat exchange also depends on the surface area of the plate,
the thickness and type of metal used in the plates, the rate and direction of flow
of the liquids and the difference in temperature between the two liquids involved
in the heat exchange process.
An approximate 3-8 mm space is maintained between the plates by a non-absorbent
rubber seal, which is bonded around the edges of the plate. The liquids, which are
sandwiched among the plates, enter and leave the interspaces through holes in the
corners of the plates. Open and blind holes route the liquids from one set of plates 31
Processing of Milk
Figure 5.4: Plate Heat Exchanger
to another. The capacity of the pasteurizer is secured by a corresponding number
of plates.
Regeneration sections: The bank of plates is usually divided into four sections
separated by connector grids with inlet and outlet bosses. In the regeneration
section, the incoming cold milk is heated by the hot pasteurized milk and the
pasteurized milk is cooled by transferring heat to the cooling medium. This heat
transfers process work most effectively when the two liquids involved flow in
opposite direction, i.e. counter current flow on either side of the plates. Regeneration
section raises the raw milk temperature from 4C to 67C and cools the pasteurized
milk from 72C to 10C. Thus, PHE saves about 92% of heating and cooling
energy. The regeneration efficiency is calculated by using the following formula:
% Regeneration = temperature increase due to regeneration/ total temperature increase
For example: The cold milk enters the pasteurizer at 4C and attains a temperature
of 60C after regeneration. The final pasteurization temperature is 72C. Calculate
the regeneration efficiency.
Increase in Temperature due to regeneration: 600C-40C=560C
Total Temperature Increase: 720C-40C= 680C
32 % Regeneration efficiency: 560C/680C = 82.36%
Steam-heated hot water or vacuum steam is used in heating section to raise the Pasteurization
partly heated raw milk to pasteurization temperature. The holding section is either
plate type or tube type. The plate type will have a number of plates. The partly
cooled pasteurized milk is further cooled in cooling section to 4C.
iv. Instrumentation
The instruments associated with the pasteurization plant are used for performing
three functions (Table 5.2).
Table 5.2: Instruments associated with pasteurizer and their functions
S.No. Type of Instrument Function(s)
1. Indicating Temperature (Milk, hot water, Chilled water),
Steam & air pressure
2. Controlling Operating the flow diversion valve, operating
the steam regulating valve in the heating
system
3. Recording functions Recording the hot and cold milk temperatures
and recording the frequency and duration of
diversions
Check Your Progress 3
1. Describe the constructional and operational details of a batch pasteurizer.
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2. Describe the steps involved in the operation of a milk pasteurizer (HTST).
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5.6 OPERATION OF PASTEURIZATION PLANT
We have studied the importance of pasteurization process and the important
components of a pasteurization plant. Now let us see the operations involved in
running of a pasteurization plant and how to cope with operational problems.
i. Starting the Plant
The following steps should be followed to start the plant:
a) Start the air compressor;
b) Switch on the control panel mains;
c) Fill the hot water tank, start the hot water pump;
d) Open the air vents
e) Start flow of the milk to the float controlled balance tank
f) Start the milk pump
g) Close the air vents when the milk coming out from them indicates that all air
has been displaced. 33
Processing of Milk h) Set the temperature controller to maintain the milk at 72C.
i) Turn on cold water and chilled water and hot water set.
ii. Shut down of the Plant
For shutting down the plant, at the end of the milk run:
a) Make available in the storage tank a sufficient quantity of water (approx. equal
to the capacity of the plant).
b) As the last milk is leaving the float balance tank, tip in the water from the tank.
c) When the last of the water is leaving the float balance, turn the three-way cock
at the finished milk outlet so that the flow is diverted to the floor.
d) Place a hose in the float balance tank and flush the plant thoroughly with water
until the discharge from the finished milk outlet becomes clear.
e) Turn off the cold water, brine or chilled water in the cooling sections.
f) Shut off the steam supply to the hot water set.
g) Admit cold water to the hot water tank and run until the plant is cold.
h) Stop the milk and hot water pumps.
i) If brine is used, flush out with running water.
j) Turn off the air supply and the main electric switch at the panel.
Thereafter, the plant must be thoroughly cleaned.
iii. Cleaning and Sterilization of the Plant
Cleaning the plant: Cleaning is done after completion of pasteurization process.
The milk supply is stopped to constant head tank by turning off the valve of
Raw Milk Storage Tank. Clarifier and homogenizer are stopped. The water is
added to the constant head tank. Hot water temperature is set at 70C. Primary
detergent solution is circulated for 20-30 minutes. Flush the system with lukewarm
water. Secondary detergent solution is circulated for 20-30 minutes. Flush the
plant with water.
Sterilization: The plant can be sterilized by hot water or sodium hypochlorite
solution. The raw milk tank and pasteurized milk tank are bypassed and hot
water (87-90C) is circulated for 10 minutes. The sterilization is done before
running the plant with milk for pasteurization.
iv. Pasteurization of milk
The operation of plant with the milk is called running of the plant. The plant is
started. It is sterilized. The plant is run on water. The standardization is done to
check the flow, operation of flow diversion valve, heating temperature and cooling
temperature. The homogenizer pressure is also set in according to requirements.
The flow of milk from raw milk tank to pasteurized milk tank is monitored.
v. Trouble shooting
Pasteurizing problems may occur during start up procedures or during the run.
When a problem occurs it is important to be able to identify the problems from the
symptoms, identify the cause of the problem and take the appropriate action towards
solving the problem. If the problem causes a delay in processing it is advisable to
turn off essential services such as steam and heating and cooling system to prevent
burn on in the heating section and a freeze up in the cooling system. The common
problems and their remedial measures are given in practical exercises. These could
be grouped in three broad areas: (i) inadequacy in achieving temperature, (ii)
chocking of plates and (iii) leaking plant assembly. The broad reasons for these are
given here.
34 (i) Inadequacy in achieving temperature : The possible reasons are: inadequate
steam supply, faulty temperature controllers, air in milk and improper assembly Pasteurization
of plates.
(ii) Chocking of plates : Fouling, high milk temperature, high milk acidity and
inadequate filtering of milk could be the reasons for chocking of the plant.
(iii) Leaking plant assembly : The reasons are: damaged and worn gaskets,
damaged plates and wrongly fitted plates.
vi. Preventive maintenance
Preventive maintenance will help to control damage, excessive wear and tear and
occurrence of accidents. Preventive maintenance can be divided into two areas, (i)
avoiding damage to the plant and equipment and (ii) observations and inspection of
plant and equipment. Avoiding damage consists of basically the careful handling of
machinery and equipment. The regular inspection of the plant and equipment is
important as a part of preventive maintenance, and may include:
a) Periodical tests may be made to check the flow rates of heating medium,
cooling medium and milk.
b) The recording instruments such as thermometers, etc must be periodically checked
for accuracy.
c) Air operated instruments should be supplied with clean air.
d) The plate surfaces and gaskets must be checked during the manual cleaning of
plants.
e) Filter cloth/filters must be changed at regular intervals.
f) The faces of the plate bar and tightening spindle should be lightly coated with
grease.
5.7 TEST FOR PASTEURIZATION EFFICIENCY
Phosphatase Test: Phosphatase test is done to determine whether milk has been
properly pasteurized or not immediately after pasteurization of milk. The test is
based on the principle that alkaline phosphatase, a natural enzyme present in raw
milk, is simultaneously deactivated by heat treatment as specified for pasteurization.
When milk-containing phosphatase is incubated with p-nitro phenyl di-sodium ortho
phosphate, it hydrolyses the substrate and, as a result, para-nitro phenol is liberated
which gives a yellow colour under alkaline condition of the test. The amount of the
yellow colour present is directly proportional to the amount of phosphatase present
in milk. The presence of yellow colour indicates inefficient pasteurization or post-
pasteurization contamination of the milk. The intensity of the colour is compared
with standard and lavibond comparator disc.
Check Your Progress 4
1. Name two methods for sterilizing the pasteurizer.
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2. Write the importance of phosphtase test.
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Processing of Milk
5.8 LET US SUM UP
Pasteurization is a key process in dairy plant operations in which heat treatment is
given to milk to destroy all pathogenic bacteria. It extends the keeping quality of
liquid milk by destroying most of the milk spoilage organisms. It safeguards public
health and ensures good quality manufactured products. There are two methods of
pasteurization of milk (i) Low Temperature Long Time (LTLT) method and (ii)
High Temperature Short Time Method (HTST). LTLT method is used in dairy
processing less than 5000 litres of milk. The most commonly method adopted
consists of heating the milk in continuous flow to a minimum temperature of 72C
and maintaining it at this temperature for not less than 15 seconds after which the
milk is rapidly cooled to 4C. This is known as the High Temperature Short Time
(HTST) process. The principal item of equipment required for HTST pasteurization
is a Plate Heat Exchanger (PHE) and usually this is of the plate type. The main
function of the PHE is to exchange or transfer of heat from a hot liquid to a cooler
one. The bank of plates is grouped into different sections called as Regeneration,
Heating and Cooling Section. The holding section can be either plate type or tube type.
Raw milk enters into Plant Heat exchange of the plate heat exchanger and its
temperature is increased from 4C to 67C. The heated raw milk is further heated
in heating section upto 72C and kept for 15 seconds and then pass through Flow
Diversion Valve (FDV) and milk is forwarded to regeneration section where properly
pasteurized milk is cooled from 72C to 10C. The cooled milk enters the chilling
section and is further cooled to 4C. The pasteurization plant is equipped with
instruments to indicate and control the temperature and also to performed the other
related functions for efficient pasteurization of milk.
Different operations like starting, sterilizing, cleaning and running of the plant should
be done in a correct way and the standardized procedure/steps should be followed
as specified by the manufacturer of the plant.
The periodic inspection of the different components of the plant is essential to
ensure its proper functioning and trouble free service.
5.9 KEY WORDS
Corrugated : bent into regular curves, folds or grooves
Taint : objectionable foreign flavour
Thermal : determined, measured or operated by heat
Thermograph : a self-registering thermometer
Turbulence : violent commotion
Valve : a dense attached to a pipe to control the
passage of air, steam or gas
Organoleptic : sensory properties flavour (smell & taste),
colour and texture
Pathogen : an agent that causes diseases.
5.10 SOME USEFUL BOOKS
Dairy Handbook. (1985). Alfa-Laval, Food Eng AB, PO Box 64, Lund, S-22100,
Sweden.
De, Sukumar. (1980). Outlines of Dairy Technology, Oxford University Press Bombay
ICAR. (2002). Handbook of Animal Husbandry, Third Revised Edition New
36
Delhi Chapter on Dairying contributed by B. N. Mathur & D. K. Pasteurization
Thompkinson
Khan M. E. (1998) Milk Processing, Dairy Technology Textbook for Class XI.
NCERT, Delhi.
NDDB. (1980). Milk Processing Manual, NDDB, PO Box 40, Anand
Manual for Milk Pasteurizer Operators. Victoria Milk Distribution Association.
5.11 ANSWERS TO CHECK YOUR PROGRESS
Your answer should include the following points:
Check Your Progress 1
1) i. To make safe for human consumption by destroying pathogenic
microorganisms present in milk.
ii. To improve the keeping quality of milk.
Check Your Progress 2
2) i. Batch, holding or Low Temperature Long Time (LTLT):63C for 30
minutes.
ii. Continuous, High Temperature Short Time (HTST): 72 C for 15 seconds.
Check Your Progress 3
3) i. The components of a pasteurization plant: milk feed pump, constant head
tank, flow controller, plate heat exchanger, filter, clarifier, homogenizer,
flow diversion valve, instruments to record temperatures, systems for
heating and cooling and piping system.
Check Your Progress 4
4) i. Two methods are (i) Hot water sterilization, and (ii) Sodium hypo chloride
sterilization.
ii. Phosphatase test is done to determine whether milk has been properly
pasteurized or not.
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