Reasons for Cooking & Heat Transfer

Why Do We Cook Food?

Cooking food in different ways alters the texture, smell, flavour, appearance and nutritional value. Here are some explanations for why we cook:

To enhance flavours

Cooking involves chemical reactions. The chemical reactions that take place alter the flavour of the food.
When cooking different foods together, their flavours combine.
Roasting intensifies flavours. When we roast meats and vegetables, they brown and become crispier (because of added fat). This happens because the water within the foods evaporates.

To preserve food for longer

Cooking food at high temperatures helps to kill any bacteria and mould present.
Pasteurising milk involves heating milk to a high temperature before cooling so that it stays fresher for longer.

To make sure it's safe to consume

Lots of foods contain dangerous toxins (e.g. rhubarb) or bacteria (e.g. sprouts and poultry) that are destroyed during the cooking process.
- For example, it's important to cook chicken properly (for long enough at a high enough temperature) to kill any Salmonella bacteria present.

To enhance texture

Many foods are harder to swallow, chew or digest pre-cooking.
Cooking softens some foods (e.g. cauliflower becomes less rigid and couscous expands as it's starch molecules become softer).
Cooking makes meats more tender because the solid fats in the meats melt and the proteins become softer. But, overcooking meats can make them tough.
Some people may prefer the textures of foods cooked in certain ways (e.g. brownies can have a soft interior and crusty exterior).

To vary a diet

Cooking allows you to enjoy foods in many different ways.
For example, you could enjoy chicken through eating:
- Roast chicken.
- Barbecued chicken skewers.
- A chicken curry.
- A chicken stew.
- A grilled chicken breast.

Methods of Heat Transfer

We use heat energy to cook. Heat energy is transferred in three ways:

Conduction

Heat energy is transferred through vibrating particles. Particles are tightly packed in solids, so vibrations pass quickly from one particle to another when they collide.
When you put a pan on a stove (hob), heat energy transfers to the pan, causing the particles in the pan to start vibrating more.
Pans are often made of metal because metal conducts heat well.
The particles pass on heat energy by colliding with other particles until heat energy has transferred throughout the pan.
When food is added to the hot pan, the particles in the pan transfer heat energy to those in the food. This process happens until the food in the pan is cooked all the way through.

Convection

Heat energy is transferred through liquids and/or gases.
When liquids are heated, the liquid closest to the heat source heats up first.
The warmer liquid rises and the cooler liquid flows beneath it.
The cooler liquid then starts to heat up as it is closer to the heat source. It rises and even cooler liquid falls beneath it.
The movement of water in this way creates convection currents. Eventually, all of the fluid is heated.
This process also takes place in ovens - where hot air rises and colder air replaces it below.

Radiation

Heat energy is transferred through radiation waves.
The heat source and food don't come into direct contact.
Microwaves warm up the water molecules, fat and sugar in food via radiation.
Toasters and grills also heat up food using radiation.
- They send out radiation waves. Food absorbs these waves and heats up.

1Food Preparation Skills

1.1Food Preparation Skills

1.1.1General Practical Skills

1.1.2Knife Skills

1.1.3Preparing Fruit, Vegetables & Using Equipment

1.1.4Cooking Methods: Prepare, Shape & Combine

1.1.5Sauce Making, Tenderising & Marinating

1.1.6Dough & Pastry

1.1.7Shaping & Finishing Dough

1.1.8Raising Agents & Mixtures

1.1.9End of Topic Test - Food Preparation Skills 1

2Food, Nutrition & Health

2.1Macronutrients

2.1.1Proteins

2.1.2Proteins 2

2.1.3Fats

2.1.4Carbohydrates

2.1.5Carbohydrates 2

2.2Micronutrients

2.2.1Fat-Soluble Vitamins

2.2.2Water-Soluble Vitamins

2.2.3Minerals & Water

2.2.4Minerals & Water 2

2.2.5End of Topic Test - Macro & Micronutrients

2.3Nutritional Needs & Health

2.3.1Informed Choices for a Balanced Diet

2.3.2Informed Choices for a Balanced Diet 2

2.3.3Energy Needs

2.3.4Nutritional Analysis

2.3.5Diet Modifications

2.3.6Diet-Related Problems

2.3.7Diet-Related Problems 2

2.3.8End of Topic Test - Nutritional Needs & Health

3Food Science

3.1Cooking of Food & Heat Transfer

3.1.1Reasons for Cooking & Heat Transfer

3.1.2Water-Based Cooking Methods

3.1.3Fat-Based Cooking Methods

3.1.4Dry Cooking Methods

3.1.5Dry Cooking Methods 2

3.2Functional & Chemical Properties of Food

3.2.1Proteins & Carbohydrates

3.2.2Fats & Oils

3.2.3Raising Agents

3.2.4End of Topic Test - Food Science

4Food Safety

4.1Food Spoilage & Contamination

4.1.1Microorganisms & Signs of Food Spoilage

4.1.2Enzymes & Signs of Food Spoilage

4.1.3Food Poisoning

4.1.4Bacterial Contamination

4.1.5Microorganisms in Food Production

4.2Principles of Food Safety

4.2.1Temperature Control

4.2.2Ambient Foods & Food Labels

4.2.3Preparing, Cooking & Serving Food

4.2.4End of Topic Test - Food Safety

5Food Choice

5.1Factors Affecting Food Choice

5.1.1Factors Which Influence Food Choice

5.1.2Food Choices

5.1.3Religious Food Choices

5.1.4Food Labels

5.1.5Mandatory Food Labels

5.1.6Optional Food Labels

5.1.7Marketing Influences

5.1.8End of Topic Test - Food Choice

5.2British & International Cuisines

5.2.1British Cuisine

5.2.2Japanese Cuisine

5.2.3Japanese Ingredients & Dishes

5.2.4Spanish Cuisine

5.2.5Spanish Ingredients & Dishes

5.3Sensory Evaluation

5.3.1Taste Receptors & Olfactory Systems

5.3.2Sensory Testing Methods

5.3.3Sensory Testing Methods 2

5.3.4End of Topic Test - Cuisines & Senses

6Food Provenance

6.1Environmental Impact & Sustainability of Food

6.1.1Food Sources - Intensive & Organic Farming

6.1.2Food Sources - Genetically Modified Crops

6.1.3Food Sources - Reared Food

6.1.4Food Sources - Caught Food

6.1.5Food & The Environment

6.1.6Food & The Environment 2

6.1.7Sustainability of Food

6.1.8Sustainability of Food 2

6.1.9End of Topic Test - Environmental Impacts

6.2Food Processing & Production

6.2.1Primary Food Processing

6.2.2Primary Food Processing 2

6.2.3Secondary Food Processing

6.2.4Fortification

6.2.5Additives

6.2.6End of Topic Test - Food Processing & Production

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