ZIMSEC O Level · Food Technology and Design · Form 1, Form 2
Why we cook food
To make it safe (kill bacteria), easier to digest, more flavoursome and attractive, and to preserve it.
Heat transfer
- Conduction: through solids (the base of a pan, frying).
- Convection: through liquids and air (boiling, oven baking).
- Radiation: by infrared rays (grilling, toasting).
Methods
- Moist heat: boiling, simmering, steaming (keeps more nutrients), stewing, poaching, pressure cooking (saves fuel and time).
- Dry heat: baking (bread, cakes), roasting, grilling.
- Fat: shallow frying, deep frying (fast but adds fat).
- Microwave cooking: fast; heats water molecules in food.
Effects of cooking
Proteins coagulate (eggs set); starch gelatinises (porridge thickens); sugar caramelises; vitamin C and some B vitamins are lost in water and with long cooking.
Saving fuel
Cover pots, cut food into small pieces, use pressure cookers, use solar or fuel-efficient stoves, and cook several items together.
Exam tip: To keep vitamin C, cook vegetables quickly in a little water with the lid on – and do not soak them.
Check yourself
- Which method of heat transfer is used in grilling?
- Give one advantage of steaming.
- What happens to starch when it is heated in water?
Show answers
- Radiation.
- Any one: keeps more nutrients, no fat added, food does not break up.
- It gelatinises – the grains swell and the liquid thickens.
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