Milk as food sustains its quality through inhibition of bacteria growth after milking. This is done by either cooling the milk to temperatures unsuitable for bacteria growth or by pasteurization to kill harmful bacteria. The ideal storage temperature is 3-4 degrees and conservational achieving pasteurization standard is 680C and above.
Cooling tanks are used to cool, store and preserve milk with minimal risk of quality deterioration. They work on the principle of heat interchange whereby the heat in the milk is removed by use of refrigerant gas, which takes the heat while losing it cold to the milk. An evaporator then reinstates the cold by use of air pressurized over the coils carrying the refrigerant. This age old principle is utilized in construction of milk cooling tanks normally referred to as direct expansion systems and ice-bank systems.
Direct expansion– these can either be closed or open. It is designed with a large refrigerant gas evaporation surface for fast dependable cooling that ensures maximum heat exchange. They range from can holding capacities of 250-3500 litres in open models and 1000 litres to 25000 litres in closed models.
Ice bank– These tanks which can also be open or closed models rely on the principle of the refrigerant gas cooling the milk through a second but faster media in the form of water. This means that the water as a media is cooled before and during milk cooling which in turn cools the milk. This principle operates in all spheres where milk is being cooled. The use of ice banks is universal and more relevant in achieving instant cooling where the milk attains storage temperatures faster than in direct expansion and also the use of less power. In smaller models of tanks an integrated ice builder/storage system is used whereby an ice water pump circulates and sprays ice water over a large surface area, ensuring even melting of the ice in the storage bank. There is no limit to the capacity of ice bank systems.