Cooking - how and why

Some food can be eaten raw, such as carrots and apples. But some food is usually cooked before it is eaten, such as meat and fish.

Ways to cook food

There are many ways to cook food, including by:

  • microwave oven
  • gas or electric oven
  • boiling
  • steaming
  • grilling
  • frying

Notice that all of these methods involve heating the food to a high temperature.

Why do we cook food?

Food may be contaminated with harmful microbes that can cause disease. The high temperatures involved in cooking kill these microbes. Cooking also makes food easier to digest. It can improve the food’s appearance, texture and flavour, too.

Cooking involves chemical changes:

  • new substances are made
  • the process is irreversible
  • an energy change occurs

For example, bread turns brown as it is toasted. Sugars in the bread break down to form carbon:

sugar and heat energy goes to water plus carbon

This change needs heat energy from the toaster, and it cannot be reversed.


Eggs and meat are good sources of protein. The protein molecules change shape as a result of the heat energy they absorb. This causes changes in the appearance and texture of the eggs and meat when they are cooked. For example:

  • Egg white solidifies and becomes white instead of transparent.
  • Meat becomes firmer and turns from red to brown.


Potatoes are a good source of carbohydrate, mainly as a complex carbohydrate called starch. Raw potato is hard and has an unpleasant taste. Potato becomes softer when is cooked, the starch is converted into simple sugars, and the potato becomes sweeter.

Baking powder is used for baking cakes. It contains sodium hydr

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