Cold Storage and Insulation

Refrigeration plays an important role in preservation of perishable commodities, i.e. to safeguard these against spoilage, particularly the food items including milk and other dairy products. The milk and dairy products although produced continually must be preserved against the time of distribution and kept until required by the consumers. This time may be weeks or even months after processing. For this reason, the principles governing the deterioration of food substances are an integral part of study of refrigeration as a whole. The deterioration or spoilage of milk and other dairy products is mainly due to bacteria growth. Bacteria are minute organisms and many species of these are found in milk and dairy products. Certain types of bacteria act upon the milk sugar or lactose to produce lactic acid, which bring about decomposition or souring of milk. The souring of milk is apparent by its disagreeable odour and bitterness of taste and it will not be suitable for human consumption. In the same way, spoilage of fatty dairy products like butter and cheese take place resulting from chemical changes of fat and oils and they emit a rancid or sour odour. All these physical and chemical changes and bacterial growth causing spoilage of dairy products can be considerably retarded in their activities by their exposure to low temperature conditions and proper level of humidity and purity of surrounding air. These favourable conditions are generated in cold storage to retard spoilage and preserve the stored products for a longer period. Thus the cold storages are designed according to favourable conditions of temperature, humidity and purity of air required for the type of dairy product to be stored. The basic principle of producing cold or low temperature in cold storage is same by using a vapour compression refrigeration system.Insulation of cold storage is also given importance because it retards the flow of heat from surrounding to the cold room and is an integral part of cold storage.

Just as in PVC electric wire used in homes, the PVC insulation covering the copper wire prevents electric current to flow from copper wire to our hand, the thermal insulation around a cold store-storage prevents inflow of outside heat. In actual all the materials offer resistance to the flow of heat but which have high resistance are called insulators. The surrounding temperature is always higher than the cold storage temperature and heat will continuously flow inside in the absence of insulation.It will make the refrigeration plant ineffective. Thus the design of proper insulation i.e. type of insulating material, its thickness, its method of fixing etc. is equally important in the design of a cold storage.