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WHAT IS PASTEURIZATION ??
Pasteurization is a heat treatment involves heating food to a
temperature that kills disease causing micro organisms and
substantially reduces the levels of spoilage organisms
Pasteurization is not intended to kill all micro organisms in the
food. Instead pasteurization aims to reduce the number of viable
pathogens so they are unlikely to cause disease
The heating may be by means of steam, hot water, dry heat, or
electric currents, and the products are cooled promptly after the
heat treatment
Heating also destroy enzymes that make milk spoil, so
pasteurized milk drinkable for long time
HISTORY OF PASTEURIZATION
The French scientist Louis Pasteur
invented pasteurization
To remedy the frequent acidity of the
local wines he found out experimentally
that it is sufficient to heat a young wine to only about 50-60˚C (122-140˚F) for a brief time to kill the microbes
Pasteurization was originally used as away of preventing wine and beer from souring, and it would be many years before milk was pasteurized
Pasteurization of milk was suggested by Franz von soxhlet in 1886
PASTEURIZATION IS USED FOR;
1.When more rigorous heat treatments might harm the quality of products
2.When one aim is to kill pathogens, as with market milk
3.When the main spoilage organisms are not very heat resistant, such as the yeasts in fruit juices
4.When any spoilage organisms will be taken care of by additional preservative methods to be employed
When competing organisms are to be killed
VAT PASTEURIZATION
The first widely used pasteurization process
for milk involved heating the milk in large
tanks or vats to 60˚C for at least 20 minutes
The holding method was subsequently
changed to 61.7˚C for 30 minutes
This was not a continuous process and was
referred to as vat pasteurization
ULTRA HIGH TEMPERATURE (UHT)
Heat treatment processes in excess of
pasteurization for milk and milk products
have been designated as very high
temperature (VHT) and ultra high
temperature (UHT)
UHT processes usually refer to
pasteurization techniques with temperature
of at least 130˚C in a continuous flow, with
holding times of approximately 1 sec.
UHT SYSTEM
Steam injection
technique
steam is
injected into milk
Steam infusion
technique
milk is
injected into steam
BATCH PASTEURIZATION (LTLT)
Milk is heated at 63˚C for 30 minutes
Can heat milk in vat or outside the vat
Here milk is heated in plate heat exchanger and send to the vat
Agitator is provided in the vat to prevent cream formation and to ensure uniform heat distribution
Then the milk is cooled and again passed through the plate heat exchanger and cooled using chilled water
PROCESS
1) cold raw milk is fed into the pasteurization plant and passes into the
regeneration heating system of the plate heat exchanger
2) The plate heat exchanger is basically a series of stainless steel plates
stacked together with some space in between forming chambers to hold
the milk as it passes through
3) In the regeneration section cold milk is pumped through the A chambers,
while milk that already been heated and pasteurized is pumped through
the B chamber
4) The heat from the hot milk passes to the cold milk through the steel
plates5) This warms the milk to 57-68˚C 6) Next the milk is passes into the heating section of plate heat exchange. Here
hot water in the B chamber heats the milk at least 72˚C which is the goal temperature for HTST
7) Hot milk is then passed though a holding tubes, it takes milk about 15 sec to pass through the tube
8) Milk is officially pasteurized once its passes through the holding tube9) Now the pasteurized milk is sent back through the regenerative section, where
it warms the incoming cold milk10) This cools the pasteurized milk to about 32˚C
TEMPERATUE TIME PASTEURIZATION TYPE
63˚ C 30 min Vat pasteurization
72˚ C 15 sec HTST
89˚ C 1 sec HHST
90˚ C 0.5 sec HHST
94˚ C 0.1 sec HHST
100˚ C 0.01 sec HHST
138˚ C 2 sec UHT
PASTEURIZATION TEMPERATURE
The sensible heat required to raise the temperature of a liquid during pasteurization is;
Q=mc(T₁-T₂)
Q= Specific rate of heat transfer
m= mass flow rate
c= specific heat capacity
T₁-T₂= Temperature difference
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