Explain about Cold Preservation - methods of food processing?

The metabolism of a living tissue is a function of the temperature of the environment. Low temperatures are used to retard chemical reactions and action of food enzymes and slow down or stop growth and activity of microorganisms in the food. Lower the temperature, the slower will be the above natural activities. Freezing and refrigeration are among the oldest methods of preservation. Mechanical ammonia refrigeration systems invented during 1875 allowed development of commercial refrigerated warehousing and freezing.