How & Why Food is Cooked Reasons for cooking food 1 To destroy harmful bacteria in food. 2. To develop the flavour of foods 3. To make food easier to bite, chew, swallow & digest. 4. To make food more appealing & attractive to eat. 5. To give people a variety of foods by using different cooking methods. 6. To give people hot food when the weather is cold 7. To destroy natural poisons in some foods & so make them safe to eat, 8. To enable food to rise, be thickened, dissolved & set when preparing a recipe

Heat Exchange Heat is a type of energy. All materials (solids, liquids, & gases), including foods are made up of very small particles called atoms. Atoms join together to form molecules As a foods is heated, its molecules absorb energy and vibrate more vigorously The faster they move, the more the temperature of the food rises. If the heat is removed the molecules become less active, reducing the foods temperature.

Methods of Heat Exchange The heat is passed from one material to another by three different methods called: Conduction Convection Radiation All of these methods are used in the application or removal of heat from a food product. One method or several may be in action at any time depending on the food and on the time and equipment available.

Conduction Is the exchange of heat by direct contact through solid materials such as metals & Food e.g. stir frying vegetables in a wok or making ice cream Good conductors of heat,such as metal & water pass the energy quickly through the food. Poor conductors such as glass,cloth,wood and plastic pass heat slowly as the materials act as insulators preventing heat energy from passing through easily. Convection Is the exchange of heat by the application of a gas or liquid current e.g boiling potatoes in hot water, frying, baking bread or blasting cold air through peas to freeze. (E,g Boiling, blast chilling) Heat energy causes molecules in a liquid or gas to expand and rise Radiation Is the passing of heat through space without the use of a solid, liquid or gas. The rays pass through the air until they come in contact with the food, some are absorbed while others are reflected. There are different type of these including infrared rays and microwaves Sun dried is a traditional method of using the suns rays to preserve food