Refrigeration is the process of keeping things cold by removing heat from them. When you put milk in the refrigerator, the machine pulls warmth out of the milk and pumps it away, keeping the milk fresh and safe to drink for days instead of hours.

Before refrigeration, people had to use ice cut from frozen lakes in winter and stored in insulated buildings, or eat only preserved foods like salted meat and dried fruit. Fresh food spoiled quickly. The invention of mechanical refrigeration in the 1800s transformed daily life: suddenly families could keep fresh meat, vegetables, and dairy products for longer. Restaurants could serve a wider variety of foods. Groceries could stock products from far away.

Refrigeration works through a clever cycle: a special fluid called refrigerant evaporates inside the refrigerator, absorbing heat as it turns from liquid to gas. Then a compressor squeezes this gas, forcing it through coils on the back of the fridge where it releases that heat and turns back into liquid. The cycle repeats continuously, steadily pulling warmth from inside and releasing it outside.

Today refrigeration is everywhere: in home kitchens, restaurants, hospitals storing medicine, trucks carrying food across the country, and even in air conditioning systems that cool entire buildings.