Chilling Center

i. Purpose

When the producer has no possibility for any mode of primary cooling, the objective should be to deliver the milk in the shortest possible time to the processing plant or collection centre. If no cooling facilities exist at the centre, its main objective is to receive all the milk from producers as quickly as possible and transport it for processing to chilling centre. The chilling centre pools, accepts and weighs the supplies of the milk from different sources, and checks the condition and quality of milk supplies. Milk is chilled immediately and stored till supplied it to the market or processor. So wherever, there is no possibility of raw milk to reach processing plant within 4 hours of production, a chilling centre is required to be established to save the milk from deterioration. This requires enforced time schedules for receiving milk at the primary collection point and a reliable delivery system to the market,processor or chilling centre. Where milk is to be mechanically cooled prior to further transportation, the most important pre-condition is also time. The arrival of milk at the chilling centre should be short for the better milk quality.

Installation of chilling center is done with the following objectives:

•  Accepting, weighing and pooling the supplies of milk.
•  Preserving the quality of raw milk supplies.
•  Providing easy transport of chilled milk to the processor.

ii. Criteria for Selection of Site and Location

Selection of a suitable site and location for establishing a milk chilling centre is guided by:

•  Location of main dairy or market,
•  Within area of adequate milk production,
•  Availability of adequate potable water supply,
•  Sufficient electric supply,
•  Proximity to a good road and/or railway station.
•  Facilities of waste/sewage disposal, and
•  Easy availability of human resources and infrastructural facilities.

iii. Operational Procedure

Essentially, this is the same as in a small dairy. On arrival, the milk is graded for acceptance/rejection, weighed, recorded, sampled for testing, cooled and stored at low temperature until dispatched to the market or processor.

Reception and Receiving Devices: Normally, milk is brought in cans to the chilling units from milk collection centers by different modes of transportation. In some small chilling centres, milk is also received directly from the producers.Depending on quantum of milk received, sources of supplies, type of milk supply containers, etc. receiving procedures and devices are provided at the reception
dock.

Chilling and Storage: As soon as the milk is received and dumped, it is pumped to storage tank through a chiller. The chilling system, that enables rapid cooling to reduce temperature to the desired level, is preferred. An ice bank system, using chilled water circulating through a plate heat exchanger to cool the milk immediately after reception, is more effective than immersing cans in chilled water, placing in a cold storage or cooling in jacketed vat with chilled water etc. The milk should be kept cold until it is despatched to processing plant. For this purpose, insulated bulk storage tanks mounted with motor-agitator and cooled by chilled water or refrigerant are the most effective.

Dispatch of Milk to Main Dairy: Once the milk is chilled, it is stored chilled in storage tank at the chilling centre till despatched to the main dairy. The chilled milk is drawn from the storage tank and filled either in cans or in road/rail milk tankers and, despatched. Before filling, each can and/or road/rail milk tanker is inspected carefully for cleaning and sanitization. Then, proper filling is ensured reducing loading and unloading time. The following steps are observed to ensure satisfactory despatch by tanker:

•   The level of milk and recorded temperature are noted.
•   Working of agitator is ensured.
•  The milk delivery line is connected from the tank to the milk pump in the tanker through the flow meter. Wherever flow meters are not provided, the quantity of milk dispatched is ascertained by tele-gauges or dipstick.
•  The outlet valve of the storage tank is opened, the milk pump is started and the milk is released into the tanker.
•  The rate of flow using any of the devices is recorded when the flow has become steady.
•  Milk is allowed to flow in the tanker to the prefixed optimum level, taking care to avoid excessive foam due to sudden rush of milk in the tanker compartments.
•  Milk pump is stopped, the tanker covers are closed and secured by locking them.
• The milk delivery valve of storage tank is closed.
• After the operation, all connected milk delivery line is dismantled, sanitized and kept ready for next day use.
•  A sample of milk is drawn and analyzed. Result is also recorded in the dispatch challan along with other information.
•  The number of cans and quantity of milk kept in cold storage for dispatch are checked.
•  If the milk is held in a storage tank, the necessary pipe line is connected and cans are filled.
•  A composite sample is drawn as per the laid down procedure, analyzed and recorded.
•  Satisfactory sealing of individual can is ensured to prevent tampering.
•  Wherever, ice-cooled cans are used, the recommended precautions are observed.

Sampling and Testing of milk: At a chilling centre, milk is to be sampled at 3 stages:

•  At milk reception dock for acceptance/rejection of milk and making payment to individual suppliers.
•  After bulking and chilling of milk kept in storage tank/vat and /or milk cans for record and verification.
•  At the time of dispatch to verify the quality of milk with the record of the receiving dairy.

Quality of milk on the reception dock is assessed by performing the platform tests.Further, milk samples are analyzed in the laboratory for chemical and microbiological quality of all accepted milk for making payments, maintaining records etc.