What are the three methods of heat transfer in cooking?

Heat is transferred by conduction, convection and radiation. Conduction is heat passing through a solid by direct contact, as in frying where the hot pan heats the food touching it. Convection is heat carried by the movement of a liquid or gas, as in boiling water or a fan oven, where hotter, less dense fluid rises and cooler fluid sinks. Radiation is heat travelling as waves without a medium, as in grilling, where infrared from the element reaches the food directly. Most cooking methods use more than one of these at once.

What is gelatinisation and where is it used?

Gelatinisation is what happens to starch when it is heated in liquid: the starch grains absorb water, swell and burst, releasing starch that thickens the liquid into a paste or gel. It is the science behind thickening sauces, gravies and custards with flour or cornflour, and behind the setting of dishes such as white sauce. It needs both heat and liquid, and continued heating with stirring gives a smooth, thickened result.

What is the difference between denaturation and coagulation of protein?

Denaturation is the first step: heat, acid or mechanical action (such as beating) unfolds the protein molecules from their natural shape, an irreversible change. Coagulation is the next step: the unfolded molecules join together and set into a firm, solid mass. Together they explain why a raw egg white turns from runny and clear to firm and white when cooked, why meat firms and shrinks, and why milk curdles when acid is added.

How do raising agents make baked foods rise?

Raising agents introduce a gas into a mixture that expands on heating to make the product light and risen. The three gases are air (beaten in by creaming, whisking or sieving, as in a whisked sponge), steam (produced when the water in a wet batter turns to vapour, as in choux pastry and Yorkshire pudding), and carbon dioxide (from baking powder, bicarbonate of soda or yeast). The gas expands in the oven, the mixture rises, and the heat sets the structure so it holds its risen shape.

Why does cooking destroy some nutrients?

Heat destroys some vitamins, especially vitamin C and the B group, which are also water-soluble and leach into cooking water. Long cooking, high temperatures, cutting food into small pieces and keeping it hot all increase the loss. Fat-soluble vitamins (A, D, E, K) and minerals are far more stable to heat, though minerals can also leach into water. The practical lesson is to cook vegetables quickly with little water, such as steaming or stir-frying, and serve them straight away to conserve the most nutrients.

SingaporeNutrition & Food Science

Food science and the effects of cooking: why we cook, heat transfer, what happens to carbohydrates, proteins and nutrients, and how raising agents work

An O-Level Food and Nutrition (SEAB 6087) overview of food science: the reasons for cooking, conduction, convection and radiation, the cooking changes in carbohydrates (gelatinisation, dextrinisation, caramelisation) and proteins (denaturation and coagulation), the effects of cooking on nutrients, and how raising agents work, with links to every dot point and a worked food-science walkthrough.

Generated by Claude Opus 4.88 min readSEAB-6087Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this module demands
Why we cook and how heat gets in
Chemical changes in carbohydrates and proteins
Nutrients and raising agents
How food science is examined
Check your knowledge

What this module demands

Food science explains the why behind cooking, and it is one of the most heavily examined parts of Paper 1, with Section B data-response and Section C essay questions on gelatinisation, denaturation, heat transfer and raising agents. It also underpins the coursework food study examination, because choosing a cooking method, a thickener or a raising agent is a food-science decision. The examiner rewards candidates who can name the change, explain the science and apply it to a real dish. This overview links every dot point and shows how the changes connect.

See the full set of dot points at /sg-o-level/nutrition-and-food-science/syllabus/food-science-and-the-effects-of-cooking.

Why we cook and how heat gets in

Start with why we cook food. Cooking makes food safer (killing bacteria), more digestible (softening fibre and gelatinising starch), more palatable (developing flavour, aroma and colour), more varied, and in some cases better preserved. Each reason has science behind it, and the strongest answers give the science, not just the word.

Methods of heat transfer explains how heat actually reaches the food: conduction (direct contact, as in frying), convection (movement of liquid or gas, as in boiling and fan ovens), and radiation (waves, as in grilling). Knowing which method a cooking technique uses lets you predict and explain its effect.

Chemical changes in carbohydrates and proteins

Carbohydrates in cooking covers three changes: gelatinisation (starch grains absorb water, swell and burst to thicken a liquid), dextrinisation (dry heat browns starch, as in toast), and caramelisation (sugar heated until it browns and changes flavour). These are the science of thickening sauces and browning baked goods.

Protein denaturation and coagulation explains the two-step change in protein: heat, acid or beating first denatures (unfolds) the protein, then it coagulates (joins and sets). This is why egg white firms, meat shrinks, and milk curdles with acid. It is the most reliable source of food-science marks, so learn the sequence precisely.

Nutrients and raising agents

The effects of cooking on nutrients ties food science back to nutrition: heat-sensitive, water-soluble vitamins (C and B group) are lost to heat and water, while fat-soluble vitamins and minerals are more stable. The practical conclusion is to cook vegetables quickly with little water and serve at once.

Raising agents explains how air, steam and carbon dioxide make baked products rise: a gas is introduced, it expands in the oven, the mixture rises, and heat sets the structure so it stays risen. Match each agent to its product (whisked air in a sponge, steam in choux, carbon dioxide from baking powder or yeast in cakes and bread).

How food science is examined

Identify the change. Questions describe a result (a sauce thickens, an egg sets, toast browns) and ask which food-science change is responsible.
Explain the mechanism. The marks are in the explanation: starch swelling and bursting, protein unfolding and joining, gas expanding on heating.
Apply to a dish. Section C essays ask you to use the science to choose a method, thickener or raising agent for a named product and justify it.

Explaining what happens when you make and bake a simple sponge

A student creams butter and sugar, beats in eggs, folds in flour and bakes the mixture. Explain the food science at each stage.

step Trapping air during creaming

Beating butter and sugar together traps tiny bubbles of air in the mixture. This air is the raising agent, and the sugar crystals help hold the bubbles in place, giving the batter a light texture before any heat is applied.

step Coagulating the egg protein

The eggs add more air and, importantly, protein. As the cake bakes, heat denatures the egg protein, unfolding it, and then coagulates it so it sets, helping to build the firm structure of the sponge around the air bubbles.

step Setting the starch by gelatinisation

The flour provides starch. As the moist batter heats, the starch gelatinises, absorbing liquid and swelling, which thickens the batter and, together with the set egg protein, forms the solid crumb that holds the risen shape.

step Rising and browning in the oven

In the oven the trapped air expands and the water turns to a little steam, so the cake rises. The set protein and gelatinised starch lock in the structure, and dextrinisation and caramelisation at the surface brown the crust and develop flavour. The result is a light, risen, golden sponge.

Food science explains the changes cooking causes. Heat reaches food by conduction (direct contact, frying), convection (moving liquid or gas, boiling and fan ovens) and radiation (waves, grilling). In carbohydrates, gelatinisation thickens a liquid as starch grains swell and burst, dextrinisation browns dry starch, and caramelisation browns sugar. In proteins, heat, acid or beating first denatures (unfolds) the protein, then coagulates (sets) it, as when egg white firms or milk curdles. Cooking destroys heat-sensitive, water-soluble vitamins (C and B), so vegetables are best cooked quickly with little water. Raising agents introduce a gas (air, steam or carbon dioxide) that expands on heating to make baked products rise before the heat sets the structure. Strong answers name the change, explain the mechanism and apply it to a dish.

Check your knowledge

A mix of recall and application questions. Attempt them, then check the solutions.

Name the three methods of heat transfer and give a cooking example of each. (3 marks)
Explain what happens to starch during gelatinisation. (3 marks)
Explain the difference between denaturation and coagulation of protein. (2 marks)
Name the three gases used as raising agents and give one product that uses each. (3 marks)
Explain why steaming conserves more vitamin C than boiling. (3 marks)

Solutions

Q1: Conduction (heat through direct contact, for example frying in a pan); convection (heat carried by moving liquid or gas, for example boiling water or a fan oven); radiation (heat as waves, for example grilling).
Q2: When starch is heated in liquid, the starch grains absorb water and swell. On further heating they burst, releasing starch into the liquid, which thickens it into a paste or gel. Both heat and liquid are needed, and stirring keeps it smooth.
Q3: Denaturation is the unfolding of protein molecules from their natural shape by heat, acid or beating, and is irreversible. Coagulation is the next step, in which the unfolded molecules join together and set into a firm, solid mass.
Q4: Air (for example a whisked sponge); steam (for example choux pastry or Yorkshire pudding); carbon dioxide (for example a cake using baking powder, or bread using yeast).
Q5: Vitamin C is water-soluble and easily destroyed by heat. In boiling, the vegetable sits in a large volume of water for a long time, so much of the vitamin dissolves into the water and is lost. In steaming, the vegetable is not submerged and cooks more quickly with less contact with water, so less vitamin C leaches out and less is destroyed, conserving more.

Sources & how we know this

Singapore-Cambridge GCE O-Level Food and Nutrition (Syllabus 6087) — Singapore Examinations and Assessment Board (2026)
Food science principles for Food and Nutrition — Health Promotion Board, Singapore (2026)