Keeping food fresh
Bacteria and mould grow quickly at room temperature, spoiling food. Cold slows them down. For most of history, people preserved food by drying, salting, smoking, pickling or storing it in cool cellars. The refrigerator made keeping food cold easy and changed how we shop, cook and eat.
Before refrigerators
| Method | How it worked |
|---|---|
| Root cellars | Underground rooms stayed cool year-round |
| Springhouses | Built over cold springs or streams |
| Ice harvesting | In winter, ice was cut from frozen lakes and stored in sawdust-insulated icehouses |
| Icebox | A wooden cabinet lined with tin or zinc; a block of ice delivered by the "iceman" kept it cool |
Ice harvesting was a big business in Canada and the northern U.S. in the 1800s. Ice from Canadian and New England lakes was shipped as far away as the Caribbean and India.
Inventing mechanical cooling
| Year | Inventor | Development |
|---|---|---|
| 1755 | William Cullen (Scotland) | Showed that evaporating liquid could create cold |
| 1834 | Jacob Perkins | First patent for a vapour-compression refrigeration system |
| 1850s–1870s | James Harrison, Carl von Linde and others | Commercial refrigeration machines for breweries and meat packers |
| 1913 | First electric home refrigerators sold | |
| 1927 | General Electric "Monitor-Top" | One of the first widely popular home fridges |
| 1930s | Freon (a CFC) refrigerant | Safer than earlier toxic refrigerants |
By the 1950s, most Canadian homes had an electric refrigerator.
How a refrigerator works
A fridge doesn’t make cold. It moves heat from inside the fridge to the outside. It uses a special fluid called a refrigerant that boils at a very low temperature.
The key idea: when a liquid evaporates, it absorbs heat. When a gas condenses, it releases heat. (That’s why sweating cools you.)
The refrigeration cycle
| Step | Part | What happens |
|---|---|---|
| 1 | Compressor | Squeezes refrigerant gas, making it hot and high-pressure |
| 2 | Condenser coils (back or bottom, outside) | Hot gas releases heat to the room and condenses into a liquid |
| 3 | Expansion valve | Liquid passes through a tiny opening; pressure drops and it gets very cold |
| 4 | Evaporator coils (inside the fridge) | Cold refrigerant absorbs heat from the food and air, evaporating into gas |
| 5 | Back to compressor | The cycle repeats |
That’s why the back of a fridge feels warm: it’s releasing the heat taken from inside.
A thermostat turns the compressor on and off to keep the fridge at about 4 °C and the freezer at about −18 °C.
Heat pumps and air conditioners use the same cycle.
Safe food temperatures
| Location | Temperature |
|---|---|
| Fridge | 4 °C or colder |
| Freezer | −18 °C or colder |
| "Danger zone" for bacteria | 4 °C to 60 °C |
Food left in the danger zone for more than two hours can become unsafe.
How refrigeration changed the world
| Area | Change |
|---|---|
| Health | Less food poisoning |
| Shopping | Families could buy groceries weekly instead of daily |
| Diet | Fresh fruit, vegetables, milk and meat available year-round |
| Food industry | Refrigerated trucks, rail cars and ships move food long distances |
| Medicine | Vaccines, blood and medicines can be stored safely |
| Science | Labs preserve samples |
Refrigerated rail cars let Canadian meat, fish and dairy reach distant markets.
Refrigerators and the environment
The ozone layer
Old refrigerators used CFCs (chlorofluorocarbons). In the 1970s and 1980s, scientists discovered that CFCs leaking into the air were destroying the ozone layer, which protects Earth from harmful UV rays. The Montreal Protocol (1987), signed in Montreal, phased out CFCs. It’s considered one of the most successful environmental agreements ever, and the ozone layer is slowly recovering.
Climate
Some replacement refrigerants (HFCs) are powerful greenhouse gases. The 2016 Kigali Amendment is phasing them down, and newer fridges use more climate-friendly refrigerants.
Energy
Fridges run all day, every day, so efficiency matters. Modern ENERGY STAR fridges use far less electricity than models from decades ago. Old fridges should be recycled properly so refrigerants don’t escape.
Common mistakes
- Thinking fridges "make cold." They move heat out.
- Thinking you can cool a room by leaving the fridge door open. The fridge would release more heat out the back than it absorbs.
- Putting hot food straight into a packed fridge. It can warm other food; let large amounts cool a little or divide into smaller containers.
Try it yourself
- Put a drop of rubbing alcohol on the back of your hand (with an adult). Why does it feel cold?
- Feel the coils or vents at the back or bottom of a fridge. Why are they warm?
- Place a thermometer in your fridge and freezer. Are they at safe temperatures?
Quick recap
- Before fridges, people used root cellars, ice harvesting and iceboxes.
- Fridges move heat from inside to outside using a refrigerant.
- The compressor, condenser, expansion valve and evaporator form the refrigeration cycle.
- Refrigeration improved health, diet, medicine and trade.
- The Montreal Protocol phased out ozone-damaging CFCs.