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Pasteurizer and Sterilizer

i. Pasteurizer
We will now study two types of pasteurizers commonly used in a dairy plant (i) Batch and (ii) Continuous type.

Batch/Holding type Pasteurizer: It is also called as Low Temperature Long Time (LTLT) Pasteurizer. Batch process is mostly preferred where small quantity of milk is handled. In this method milk is generally heated to 63 o C and held for 30 minutes and then cooled to 5 o C or below. Here indirect heating is done by means of hot water.

Continuous type Pasteurizer: The other most common method is High Temperature Short Time (HTST) or Flash pasteurization (Figure-2.8). In this process,milk is heated to above 72 o C temperature for a period of about 15 seconds in continuous manner and promptly cooled. It is a plate heat exchanger type assembly,having different sections such as heating, regeneration and cooling, in a single compact equipment assembly. This type of pasteurizer is equipped with different accessories like float control balance tank (FCBT), filter, pump, hot water mixing battery, flow diversion valve (FDV), temperature indicator and recorder, etc., to ensure uninterrupted flow of milk by continuous operation. Hot water at a 90-95 o C temperature is used as heating medium and chilled water at 1-2 o C temperatures is used as cooling medium. This is energy efficient system but expensive in terms of initial cost.

ii. Sterilizers

In the process of sterilization, all the microorganisms are supposed to be destroyed.The milk is heated to 109-115 o C for 20-40 min, in bottles and in a batch while 135-150 o C for 2-6 sec only in the continuous type of systems for large capacity operations. Sterilized milk is then aspectically filled in sterile containers. This milk can be stored at room temperature for 3 to 6 months. Usually this system is very expensive.

Batch sterilizer: In this sterilizer, milk is filled in the glass bottles and capped.These bottles are placed in baskets or carriage and locked in stationary autoclave.Autoclave is a high-pressure vessel, stationary or mobile, hooked with steam connection on heating. Heat is transferred uniformly in the bottle for better treatment.Also these autoclaves are made to revolve to facilitate faster heating. It takes little long to bring the desired temperature. Thereafter, the temperature is maintained for 20-40 minutes to achieve sterilization. After this holding, the steam/condensate is drained and bottles are allowed to cool slowly. Final temperature of the bottle/milk is brought down to 30-36 o C. The sterilizer has thermometer, steam pressure gauge,convenient loading and unloading provision. For better results, these instruments should be maintained properly.

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