Frozen food keeps for a long time because the freezing of the water inside the food forces the bacteria, which cause it to decompose, into inactivity. Like all living things, bacteria need water in order to thrive.
Bacteria are microscopic organisms or forms of life which occur in air, water and soil all over the world. But they flourish and multiply particularly wherever organic matter is present. Some may cause disease, others are harmless, or even beneficial, but their inactivity causes organic matter, including food, to decompose.
Modern discoveries have enabled sub-zero temperatures to be obtained by cooling air to about -300degrees Centigrade (-508degree Fahrenheit) by compressing it and passing it into low pressure chambers through fine nozzles. The result is a sudden and violent expansion causing the air to be drastically cooled. In home refrigerators Freon-12 gas is used instead of air and the temperatures are much less drastic. The temperature in the freezing compartment of a domestic refrigerator is about -4degrees or 25degree Fahrenheit and that of deep-freezer about -15degree centigrade or 5degree Fahrenheit.