1. Sterilized milk.pptx

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: Keep without deterioration, i.e., remains stable and be of good commercial value for a sufficient period to satisfy commercial requirements. Be free of micro-organisms harmful to consumer health, i.e., pathogenic, toxinogenic germs and toxins. 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.

5. DETAILS OF MANUFACTURE: 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. The intake milk should be promptly cooled to 5◦c for bulk storage in order to check any bacterial growth, 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.

6. 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.

7. 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.

8. STERILIZERS: These may be: 1. Batch; 2. Continuous. 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.

9. 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: I n 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.

10. 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.

11. 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.

12. THANK YOU