A refrigerator (colloquially fridge) consists of a thermally insulated compartment and a apparatus (mechanical, electronic or chemical) that transfers heat from its inside to its external environment in order that its inside is cooled to a temperature below the space temperature. Refrigeration is an important food storage technique in developed countries. The lower temperature lowers the reproduction rate of bacteria, therefore the refrigerator reduces the speed of spoilage. A refrigerator maintains a temperature a couple of degrees above the melting point of water. Optimum temperature range for perishable food storage is 3 to five °C (37 to 41 °F). an identical device that maintains a temperature below the melting point of water is named a freezer. The refrigerator replaced the icebox, which had been a standard home appliance for nearly a century and a half.