INTRODUCTION (WEEK 2)

Refrigerator

A refrigerator (colloquially fridge) is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Cooling is a popular food storage technique in developed countries and works by decreasing or even arresting the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs.

A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F).[1] A similar device which maintains a temperature below the freezing point of water is called a freezer. The refrigerator is a relatively modern invention among kitchen appliances. It replaced the icebox, which had been a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an icebox.

Freezer units are used in households and in industry and commerce. Most household freezers maintain temperatures from -10 to 0 °F (-23 to -18 °C), although some freezer-only units can achieve −30 °F (−34 °C), and lower. Refrigerators generally do not achieve lower than -10 °F (-23 °C), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests (resembling upright units laid on their backs). Many upright modern freezers come with an ice dispenser built into their door

Some refrigerators are now divided into four zones to store different types of food:

−18 °C (−0 °F)	Freezer
0 °C (32 °F)	Meats
5 °C (41 °F)	Refrigerator
10 °C (50 °F)	Vegetables

Table 1: Temperature

The capacity of a refrigerator is measured in either litres or cubic feet. Typically the volume of a combined refrigerator-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 liters (4.94 cubic feet) for the refrigerator, although these values are highly variable.

Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37 to 41 °F)[1] is ideal for the refrigerator compartment and −18 °C (−0 °F) for the freezer. Some refrigerators are required to be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area such as a garage.

European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers.

Temperature	Time Storage
min temperature = −6 °C (21 °F).	Maximum storage time for (pre frozen) food is 1 week
min temperature = −12 °C (10 °F).	Maximum storage time for (pre frozen) food is 1 month
min temperature = −18 °C (−0 °F).	Maximum storage time for (pre frozen) food is between 3 and 12 months depending on type (meat, vegetables, fish, etc

Table 2: Temperature And Time