AQA GCSE Food Preparation and Nutrition: Student Book

Different methods of transferring heat to food In order to cook food, heat energy has to be transferred to it from a source of heat on the cooker hob or in the oven – either gas flames or an electric element or from fire (e.g. in a barbeque). Heat energy is transferred to food in three ways, as shown in the table below: • Conduction. • Convection. • Radiation. Study tip When you answer a question on why food is cooked: 1. Make a point 2. Explain your point 3. Include examples and reasons for your answer that are directly linked to the question. Stretch and challenge activity Extend your mind map to give reasons why the different ways of cooking your chosen food are used (e.g. for food safety, to develop flavour/texture etc.). Conduction Method of heat transfer What happens? • Cooking pans and baking tins are usually made from any of these metals: iron, steel, stainless steel, copper or aluminium. • Metal is a very good conductor of heat. This is because of its atomic structure. • Some materials, such as wood, some plastics and thick materials such as cotton and wool are poor conductors of heat. They are called heat insulators. • When we heat a metal pan on the hob, or a baking tin in the oven, it quickly heats up and transfers heat energy to the food inside. • It does this by the process of conduction. • The atoms that make up metals are tightly packed together in a lattice: • As the heat energy from the cooker hob or oven is transferred into the pan, it makes the metal atoms start to vibrate . • As they vibrate, they knock against adjoining atoms and pass on the heat energy, then they pass it on to others, and so on. Why food is cooked 85