About Sterilized milk

1. STERILIZED MILK

2. DEFINITION:
• Sterilized milk may be defined as (homogenized) milk
which has been heated to a temperature of 100◦c or above
for such lengths of time that it remains fit for human
consumption for at least 7 days at room temperatures.
REQUIREMENTS:
• Sterilized milk must:
1. Keep without deterioration, i.e., remains stable and be of
good commercial value for a sufficient period to satisfy
commercial requirements.
2. Be free of micro-organisms harmful to consumer health,
i.e., pathogenic, toxinogenic germs and toxins.
3. Be free of any micro-organisms liable to proliferate, i.e.,
it should not show signs of bacterial growth.

3. ADVANTAGES:
• Remarkable keeping quality (does not need
refrigerated storage).
• No cream layer/ plug
• Forms a soft digestible curd, and hence useful for
feeding of infants and invalids.
• Distinctive ‘rich’ flavour (due to homogenization).
• Economical to use.
• Less liable to develop oxidized taints.

4. DISADVANTAGES:
• Increased cost of production;
• More loss in nutritive value than pasteurization (50
percent of the vitamin C and 33 percent of vitamin B
originally present are destroyed and there is a slight
reduction in biological value of the milk proteins).
• Gerber test by normal procedure not so accurate.

6. DETAILS OF MANUFACTURE:
1. The raw milk, on receipt, should be strictly examined
by the prescribed physico-chemical and
bacteriological tests and only high quality milk should
be used for production of sterilized milk. Care should
be taken to accept milk supplies which has no
developed acidity and which contains the least number
of spore-forming bacteria.
2. The intake milk should be promptly cooled to 5◦c for
bulk storage in order to check any bacterial growth,
3. Next, it should be pre-heated to 35-40◦c for efficient
filtration/ clarification, so as to remove visible dirt,
etc., and to increase its aesthetic quality.

7. • The milk should again be cooled to 5◦c so as to
preserve its quality.
• It should be standardized to the prescribed
percentages of fat and solid-not-fat content in order to
conform to legal standards.
• It must be stored at 5◦c until processing.
• The milk should be promptly pre-heated to 60◦c for
efficient homogenization to prevent any subsequent
formation of a cream layer; usually single-stage
homogenization is carried out at 2500 psi pressure.
• The homogenized milk must be clarified so as to
remove the sediment formed during the
homogenization process.

8. • The hot milk must from the homogenizer should be
filled into the (hot) cleaned and sanitized bottles coming
from the bottle machine and then sealed with special
caps (crown seal type).
• The filled and capped bottles should then be placed in
metal crates for sterilization by Batch process, or fed
into conveyors for the Continuous process.
• Usually the milk is sterilized at 108-111◦c for 25-35
minutes.
• The sterilized milk bottles should be gradually cooled to
room temperature. Any sudden cooling may lead to
bottle breakage.
• Finally the milk-in-bottles should be stored in a cool
place.

9. STERILIZERS:
• These may be: 1. Batch; 2. Continuous.
1. BATCH:
• These may be rotary or non-rotary in type. The batch
sterilizers are rectangular, horizontal, boiler shaped retorts
with a steam inlet and condensate outlet, fitted with clamp-
down covers, into which steam is adjusted for the required
temperature and time for sterilization.
• In batch-rotary type, the filled bottles are put into holders
which are rotated at 6-7 rpm.
• The sterilized milk is slightly better quality in rotary type
than in non-rotary ones.
Advantages:
• Simplicity and flexibility of operation
• Less initial capital and recurring expenditure.

10. Disadvantages:
• Usually produces a brownish appearance and cooked
taste in the finished product.
• Sterilization may be faulty.
• Cooling has to be slow to avoid breakage.
• Economic advantages of large-scale processing are not
obtained.
CONTINUOUS:
• In this type, the filled and sealed milk bottles are
automatically placed by means of a slat conveyor into
the pockets of carrier cages. Then they are passed into
water at or near boiling temperature; from there, they
enter the sterilizing zone, which consists of a steam
chamber at 108-111◦c. Here the bottles remain for a pre-
determined time of 25-30 minutes.

11. Cooling:
• After heat-treatment in the batch/ tank sterilizers, the
milk bottles may be cooled in air or water. If cooling
is too rapid, the bottles may crack; if too slow, there is
a danger of browning due to caramelization. In the
continuous system, after leaving the sterilizing zone,
the bottles enter a column of hot water where the
cooling process begins. This is followed by their
passage through another tank of water for further
cooling, and conveyed to a point where they are
placed in crates in which they are transferred to the
storage room.

12. ULTRA HIGH TEMPERATURE METHOD OF
PASTEURIZATION:
• In these processes, the milk is heated to 135-150◦c for a
few seconds, generally in a plate or tubular heat-
exchanger. The milk, which is then almost sterile, has to
be filled into containers for distribution; the filling has to
be done aseptically. In many cases pre-sterilization, as
above, is followed by in-bottle sterilization.
TESTS:
• Turbidity test and bacterial count.
FAULTS:
• The most common is browning. Because of this fault,
plain sterilized milk is not so popular. Flavoured
sterilized milk is more popular.

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