Why does food stay fresh longer in the fridge?

Think about opening the fridge door. A puff of cool air brushes your fingers, and the milk bottle feels chilly in your hand. Inside, the cheese, the yogurt and last night's soup all wait on their shelves.

Now picture a glass of milk left on the kitchen table on a hot afternoon. By the next day it smells sour, and nobody wants to drink it. The same milk in the fridge stays good for days. So why does food stay fresh longer in the fridge?

Food goes bad because of bacteria, which means tiny living things far too small for your eyes to see. Bacteria live in the air, on our hands and on the food we eat. You cannot see them, but they are busy all the time.

Bacteria feed on little bits of the food they sit on. Each one that eats well splits in two, and then those two split again. Soon a handful of bacteria turns into millions.

When millions of bacteria crowd onto food, the food starts to spoil, which means it goes bad and turns smelly, slimy or sour. That sour milk on the table was full of hungry bacteria.

Bacteria love warmth. On a warm kitchen counter they eat fast and split fast, so their crowd grows bigger every hour. That is why food left out in the warm spoils in a day or two.

A fridge works all day and all night to keep its inside cold, nearly as cold as ice but not cold enough to freeze the milk. Every jar and box on its shelves gets chilly too. So what do you think happens to the bacteria on that cold food?

The cold slows the bacteria right down. They eat slowly and split slowly, as if they were feeling sleepy. The cold does not get rid of them, so food in the fridge still spoils in the end, only much later.

Bacteria and spoil. The fridge keeps food cold, and the cold slows down the bacteria, so they take much longer to make the food spoil.

Next time you feel that cool puff of air from the fridge, you can smile and think of all those sleepy little bacteria taking their slow, chilly rest.