How it works: Keeping food cold and fresh longer

Before mechanical refrigeration systems were introduced, ice harvesting, using ice and snow to cool food, was the only method of food refrigeration.

Image used for representational purposes.

Refrigeration is the practice of food storage, to extend its life, longevity and freshness, while avoiding decomposition. This cooling process applies to “the removal of unwanted heat from an object, substance, or space and its transfer to another object, substance, or space”. The heat removal lowers temperature and may be accomplished by the use of ice, snow, chilled water, or mechanical/electrical means.

Refrigeration slows down the metabolism of organic matter to a near standstill -18°C (the international standard for frozen products). At this temperature, the partial or total inhibition of altering processes in food, such as certain enzymatic reactions or the metabolic degradation of proteins, is achieved.

Before mechanical refrigeration systems were introduced, ice harvesting, using ice and snow to cool food, was the only method of food refrigeration. The Chinese harvested ice from rivers and lakes in winter as early as 1000 BC, as a natural form of refrigeration. The Inuits and Eskimos inhabiting the Arctic Circle experience harsh long winters every year. They have accordingly learned and perfected the use of their chilly surroundings to refrigerate food year-round. Without modern refrigerators, freezers, or electricity, Alaskan Eskimos dig a pit near the home (igloo) 2-3 feet deep, below the permafrost line, where fresh food is stored and kept cool, even in the summer.

The first known artificial form of refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748. However, it was only in 1913 that the first home electric refrigerator came on the scene, after a century of iterations, when American Fred W Wolf featured a refrigeration unit on top of an icebox.

Modern refrigerators are far more cutting-edge. However, the refrigeration cycle is composed of five basic components: Fluid Refrigerant; a Compressor, which controls the flow of refrigerant; Condenser Coils (on the exterior); Evaporator Coils (on the interior); and an Expansion Device. They interact with each other to keep food cool. How?

• The compressor constricts the refrigerant vapor, raising its pressure, and pushes it into the exterior coils
• When hot gas in the coils meets the cooler air temperature of the kitchen, it turns into liquid
• Now in liquid form at high pressure, the refrigerant cools as it flows into the coils inside the freezer and the fridge
• The refrigerant absorbs the heat inside the fridge, cooling the air down
• Finally, the refrigerant evaporates to a gas, flowing back to the compressor, where the cycle repeats
• Freezers use the same technology, albeit maintaining a lower overall temperature -- well below 0°C.

Most refrigerators some years ago used CFCs (chlorofluorocarbons), because they provided a stable way to keep themselves cold. But studies showed that their emission affected the Ozone Layer, and innovators worked on more sustainable solutions.

Modern refrigerators do not use CFCs, and have opted for another type of gas called ‘HFC-134a’, also called tetrafluoroethane.

Today’s refrigerators are mostly designed for sustainability, extending the shelf life of food, reducing waste, and saving resources. Also, their energy efficiency corresponds to their overall lower carbon footprint.