Foods and Nutrition · Lesson 8

Principles of cooking, heat transfer, cooking methods and terms, additives and adulteration

WAECNECO

What the syllabus asks

WAEC: Food preparation: principles underlying cooking (concept, reasons); methods of cooking (moist heat, dry heat; effects of heat on food commodities); transfer of heat (convection, radiation, conduction); cooking terms; food additives (definitions, types, functions, selection and use, food adulteration). Builds on he7.

NECO: Food preparation: principles underlying cooking (concept, reasons); methods of cooking (moist heat, dry heat; effects of heat on food commodities); transfer of heat (convection, radiation, conduction); cooking terms; food additives (definitions, types, functions, selection and use, food adulteration). Builds on he7.

What you will learn

Explain the concept of cooking and reasons for cooking.
Describe and apply the three methods of heat transfer.
Describe moist-heat, dry-heat and fat-based methods with examples.
Explain the effects of heat on food commodities.
Define common cooking terms and scale recipes.
Classify food additives and explain their functions, selection and use.
Explain food adulteration and simple ways to detect it.

Key points

Concept of cooking and reasons.
Conduction, convection, radiation; energy calculation.
Moist-heat methods and pressure cooker safety.
Dry-heat and fat-based methods; combination methods.
Effects of heat on commodities; conserving nutrients.
Cooking terms A to G.
Cooking terms H to Z; scaling recipes; °C to °F.
Food additives: types and functions.
Selection and use of additives; adulteration and checks.
Nigerian seasonings and flavourings.
Practical: demonstrating cooking methods.

Start here: The concept of cooking and reasons for cooking

Cooking is the application of heat to food to make it safer, more digestible, more attractive and tastier. It involves physical and chemical changes in the food: proteins coagulate, starch gelatinises, fats melt, sugars caramelise, fibres soften, water evaporates and flavours develop. Cooking is also a skill and an art: the same ingredients give very different results in the hands of a skilled cook.

Reasons for cooking food

To make food safe by destroying bacteria, parasites (tapeworm cysts in meat), and natural toxins (cyanogens in cassava, lectins in beans).
To make food more digestible: starch is gelatinised; tough connective tissue becomes gelatin; cellulose softens.
To improve flavour: browning (Maillard reaction, caramelisation), release of aromas (frying onions, toasting egusi), blending of spices.
To improve appearance and colour: golden fried plantain, brown bread crust.
To improve texture: tender yam, crisp chin-chin.
To provide variety: yam can be boiled, pounded, fried, roasted or made into porridge.
To stimulate appetite through aroma and attractive appearance.
To combine foods into new dishes (stews, soups, cakes).
To preserve food for a short time: cooked food keeps longer than raw, and heat is the basis of many preservation methods.
To provide hot food, which is comforting and satisfying, especially in cold weather and for the sick.

Disadvantages of cooking

Loss of heat-sensitive vitamins (C, thiamine, folate), leaching of minerals and vitamins into cooking water, formation of harmful compounds by burning and repeated frying, loss of texture and colour by overcooking, and use of fuel and time.

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Practice questions

1. Heat transfer through a metal pot base is by

conduction
radiation
convection only
evaporation

Show answer

A: conduction
Through solids.

2. Heat transfer in grilling is mainly by

conduction
convection
induction only
radiation

Show answer

D: radiation
Infrared from the heat source.

3. Movement of hot water in a pot heats food by

conduction only
refraction
convection
radiation

Show answer

C: convection
Currents in liquids.

4. Heating 2 kg of water by 75 °C needs about

75 kJ
627 kJ
150 kJ
4,180 kJ

Show answer

B: 627 kJ
2 × 4.18 × 75.

5. A pressure cooker cooks faster because water boils at about

120 °C
80 °C
100 °C
60 °C

Show answer

A: 120 °C
Raised pressure raises boiling point.

Key words

Conduction: Heat transfer through solids.
Convection: Heat carried by moving liquid or gas.
Radiation: Heat transfer by rays.
Simmer: Cook just below boiling.
Poach: Cook gently in liquid.
Braise: Brown then cook slowly with little liquid.
Steam: Cook in steam from boiling water.
Baste: Spoon fat over roasting food.
Bain-marie: Water bath for gentle cooking.
Fold in: Mix gently to keep air.
Marinate: Soak in seasoned liquid.
Parboil: Partly boil.

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