Why we cook and how heat is carried
Cooking makes food safe (kills germs), easier to digest (softens fibre, swells starch), and tastier and more attractive (new flavours, colour and texture).
Heat reaches food by conduction (touch), convection (moving water, oil or air) and radiation (rays from a grill). Methods are grouped by the medium: water/steam (moist), air or metal (dry), or fat (frying). Combination methods use two: braising and stewing (brown, then simmer in a little liquid).
Moist-heat and dry-heat methods
Moist heat
- Poaching (70–80 °C): liquid barely moves. Eggs, fish, fruit.
- Simmering (85–95 °C): small bubbles. Stocks, soups, dal, curries.
- Boiling (100 °C): big rolling bubbles. Rice, pasta, potatoes.
- Steaming (100 °C): food sits above water. Idli, dhokla, momos, vegetables; keeps more vitamins.
- Pressure cooking (about 120 °C): steam trapped in a sealed pot. Saves time and fuel.
- Blanching: dip in boiling water briefly, then cold water. Keeps colour.
Dry heat and fat
- Baking and roasting (160–220 °C): hot air in an oven. Bread, cakes, meat, vegetables.
- Grilling / broiling / tandoor (250 °C+): strong radiant heat. Kebabs, tikka.
- Sautéing / stir-frying: little oil, high heat, keep food moving.
- Shallow frying and deep frying (170–190 °C): food partly or fully in oil. Too cool = greasy; too hot = burnt outside, raw inside.
Microwave cooking heats the water inside food using waves; it is fast but does not brown.
Soups and salads
Stock is a flavoured liquid made by simmering bones or vegetables with onion, carrot, celery and herbs. It is the base of most soups and sauces.
- Clear (thin) soups: broth, consommé (stock made crystal clear), clear vegetable soup.
- Thick soups: purée (blended vegetables or lentils), cream soup, velouté (thickened with a roux of flour and butter), bisque (shellfish), chowder.
- Special/national soups: minestrone, French onion, gazpacho (cold), rasam, mulligatawny.
A salad has four parts: base (greens), body (main ingredients), garnish (colour and finish) and dressing (vinaigrette 3 oil : 1 acid, mayonnaise or yoghurt based). Types: green, vegetable, fruit, bound (potato, chicken), main-course, and side. Keep salads cold and crisp; dress just before serving so leaves do not wilt.
Egg cookery
Eggs are cooked by many methods: boiled (soft about 6 min, hard about 10 min), poached (cracked into simmering water with a little vinegar), fried (sunny side up, over easy), scrambled (bhurji), omelette (plain, Spanish, masala), and baked.
Eggs also do jobs in cooking: bind (cutlets), coat (crumb fry), thicken (custard), emulsify (mayonnaise), aerate (whisked whites in cakes), glaze (egg wash).
Freshness test: a fresh egg sinks and lies flat in water; a stale one floats. Overcooking makes eggs rubbery and gives a green-grey ring around the yolk.
Try it
With an adult, put two eggs in boiling water. Take one out at 6 minutes and one at 10 minutes, cool them and cut them open. Compare the yolks, then check with the slider in step 6.
Key formulas and definitions
- Poach 70–80 °C · Simmer 85–95 °C · Boil 100 °C · Steam 100 °C · Pressure cook ≈ 120 °C
- Bake/roast 160–220 °C · Deep fry 170–190 °C · Grill 250 °C+
- Browning starts above ≈ 150 °C (only dry heat or oil)
- Vinaigrette = 3 parts oil : 1 part vinegar or lemon juice
- Egg white sets ≈ 62–65 °C · Yolk sets ≈ 65–70 °C
- Salad = base + body + garnish + dressing
Worked examples
1. You need 200 ml of vinaigrette. How much oil and how much lemon juice?
Ratio 3 : 1 makes 4 parts. One part = 200 ÷ 4 = 50 ml. Oil = 150 ml, lemon juice = 50 ml.
2. Why do chana cook faster in a pressure cooker than in an open pan?
The sealed cooker traps steam, so pressure rises and water boils at about 120 °C instead of 100 °C. Hotter water softens chana faster.
3. Name the method: idli batter in moulds over boiling water.
Steaming, a moist-heat method at about 100 °C.
Common mistakes
- Thinking a hard boil cooks faster than a simmer; both water temperatures are close to 100 °C, boiling only breaks delicate food.
- Frying in oil that is not hot enough, so the food soaks up oil and turns greasy.
- Adding dressing to a green salad long before serving, so the leaves go limp.
- Boiling eggs too long, which makes them rubbery with a green ring.