Why do we cook food, how does heat travel into food, and what are the main methods of cooking?
Why food is cooked and how heat is transferred: conduction, convection and radiation, and the main moist, dry and fat-based cooking methods with their effects on food.
A focused answer to the WJEC Food Preparation and Nutrition science of food topic on cooking, covering the reasons for cooking, heat transfer by conduction, convection and radiation, and the main moist, dry and fat-based cooking methods and their effects.
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What this dot point is asking
You need to know why we cook food, the three ways heat is transferred (conduction, convection and radiation), and the main cooking methods (moist, dry and fat-based) with their effects on food.
Why we cook food
Cooking food:
- makes it safe to eat, as heat kills harmful bacteria,
- makes it easier to digest (for example, starch gelatinises and protein coagulates),
- improves flavour, colour and texture and makes food more appealing,
- gives variety and lets us eat foods that are inedible raw (such as dried beans),
- can preserve food and extend its shelf life.
How heat is transferred
- Conduction example: a metal pan heats and conducts heat into food frying in it.
- Convection example: boiling water and a fan oven set up currents that cook the food.
- Radiation example: a grill and a toaster send rays straight onto the food.
Many methods use more than one: an oven uses convection (hot air) and conduction (the hot tray).
Moist methods
These cook food in water or steam:
- Boiling (in water at 100 degrees Celsius): pasta, rice, vegetables; loses some water-soluble vitamins.
- Steaming (over boiling water): keeps more vitamins, gentle, fat-free.
- Poaching (in liquid below boiling): eggs, fish.
- Stewing and simmering (long, gentle cooking in liquid): tougher meat becomes tender.
Dry methods
These use dry heat without water:
- Baking (in the oven): bread, cakes, potatoes.
- Roasting (in the oven with some fat): meat, vegetables; browns and adds flavour.
- Grilling (radiant heat from above): meat, fish, toast; fat-free, lets fat drip away, but can dry or burn.
Fat-based methods
These cook food in hot fat or oil:
- Shallow frying and stir-frying: quick, adds flavour, but adds fat.
- Deep frying: crisp results, but high in fat.
How cooking changes food
Each method changes food in several ways, and the exam often asks you to link a method to its effect:
- Texture: stewing makes tough meat tender; baking sets a cake; frying makes a crisp surface.
- Flavour and colour: dry methods (roasting, grilling, frying) brown food through the Maillard reaction and caramelisation, adding flavour; moist methods do not brown.
- Nutritional value: boiling loses water-soluble vitamins into the water; grilling lets fat drip away; frying adds fat and energy.
- Safety: heating to a high enough core temperature (at least 75 degrees Celsius) kills harmful bacteria.
Choosing a method is therefore a balance of the result you want, the food, and how healthy the dish should be.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style6 marksExplain how heat is transferred to food by conduction, convection and radiation, giving a cooking example of each.Show worked answer →
A 6-mark question. Mark it for a clear explanation of each method with a correct example.
Conduction is the transfer of heat through a solid by direct contact, as heat passes from particle to particle. For example, a metal pan heats up and conducts heat into a sausage frying in it. Convection is the transfer of heat through a liquid or gas by moving currents: hot, less dense liquid or air rises and cooler liquid or air sinks to take its place, setting up a current. For example, boiling water and a fan oven cook by convection. Radiation is the transfer of heat as rays (infrared) without needing particles, travelling in straight lines to the food. For example, a grill and a toaster cook by radiation.
A top answer defines each method correctly and gives a matching example. Reward: conduction through solids by contact; convection by currents in liquids or gases; radiation by rays.
WJEC style4 marksCompare boiling and grilling as methods of cooking, including one advantage of each.Show worked answer →
A 4-mark question. Award marks for points comparing the two methods.
Boiling is a moist method, cooking food in water at 100 degrees Celsius by convection; it is fat-free and good for foods such as pasta, rice and vegetables, but some water-soluble vitamins are lost into the water. Grilling is a dry, fat-free method using radiant heat from above; it browns and adds flavour, is quick, and lets fat drip away, which is healthier for foods such as meat and fish, but it can dry food out and burn it if not watched.
Markers reward comparison points: boiling is moist, fat-free, loses some vitamins; grilling is dry, browns and lets fat drip away but can dry or burn. An advantage of each is required.
Related dot points
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Sources & how we know this
- WJEC Eduqas GCSE Food Preparation and Nutrition specification (from 2016) — WJEC Eduqas (2016)