The Purpose of Refrigeration

The fundamental reason for having a refrigerator is to keep food cold. Cold temperatures help food stay fresh longer. The basic idea behind refrigeration is to slow down the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the food.

Years ago, before refrigerators were a common appliance, they used blocks of ice to keep the food from spoiling.
A delivery truck use to drive through the neighborhoods and sell this ice. I recall hearing kids running behind the
truck and picking the pieces that fell from the truck. We have really taking refrigerators and ice machines for
granted sometimes. What would we do without them?

For example, bacteria will spoil milk in two or three hours if the milk is left out on the kitchen counter at room temperature. However, by reducing the temperature of the milk, it will stay fresh for a week or two -- the cold temperature inside the refrigerator decreases the activity of the bacteria that much. By freezing the milk you can stop the bacteria altogether, and the milk can last for months (until effects like freezer burn begin to spoil the milk in non-bacterial ways).