Cooking Methods and Food Preservation

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1Summary 重點摘要

Cooking splits into moist-heat and dry-heat methods, moving heat into food by conduction, convection, radiation and microwaves; preservation holds microbes back to extend shelf life. Knowing each method, caring for kitchen aids and working safely let you plan a meal systematically.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Purpose and effects of cookingCooking aims to make food safer, more digestible and more delicious: heat kills most disease-causing bacteria, proteins set and become easier to digest, starch gelatinises for a better texture, and colour, aroma and flavour improve. But cooking also changes nutrition: water-soluble vitamins are lost in long boiling and hot oil oxidises fats. For example, broccoli boiled for ten minutes loses much of its vitamin C into the water; steaming it for three or four minutes keeps far more nutrients and a brighter green — which is why the method must suit the ingredient.
2. Moist-heat: steaming, boiling, blanching, braisingMoist-heat methods use water or steam, below 100°C: steaming cooks by water vapour and keeps natural flavour and nutrients, ideal for fresh fish and dim sum; boiling cooks food in water for soups, congee and noodles; blanching cooks briefly in boiling water, keeping vegetables green and crisp; braising browns the food first then simmers it slowly in a little liquid until tender, like braised beef brisket. For example, steam a fish on ginger and spring onion, in only after the water boils, on high heat for about eight minutes — just cooked and silky; steaming too long makes the flesh coarse, so timing and heat control are everything.
3. Dry-heat: stir-frying, pan-frying, deep-frying, bakingDry-heat methods use hot air or hot oil at higher temperatures: stir-frying tosses food quickly over a fierce flame with little oil, keeping vegetables crisp; pan-frying browns both sides in a moderate amount of oil; deep-frying submerges food in hot oil for a crisp outside but absorbs much oil and should not be frequent; baking cooks in the oven's hot air, as for chicken wings and cakes; roasting uses an open flame. For example, stir-fried choy sum with oven-baked chicken thighs makes a good dinner: quick stir-frying keeps more vitamins, and baking renders out the fat of the skin — both lighter than deep-fried food.
4. Three ways heat travelsHeat reaches food in three ways: conduction passes heat by direct contact from the hot pan to the food touching it; convection carries heat as heated liquid or gas rises and cooler matter sinks, as in rolling soup; radiation sends infrared heat straight to the surface, as from a barbecue grill or oven element. The microwave oven works differently — microwaves make the water molecules inside the food vibrate and generate heat. For example, when baking a cake, the oven heats by radiation and convection while the heat moves into the centre by conduction — the three ways often appear together.
5. Using the microwave safelyThe microwave oven saves time and energy, and clear safety rules apply: use only containers marked microwave-safe in glass or ceramics — metal ware and bowls with gilt rims reflect the microwaves and spark, so they must never go in; eggs in shells and sealed packages burst as they expand, so break or open them first; after heating liquids, stir and let them stand a moment to avoid sudden overflow and scalds. For example, when reheating rice, cover it with a microwave-safe lid left slightly open and stir once midway, so the grains heat evenly, no cold centre remains, and the risk of leftover bacteria is reduced.
6. Principles of food preservationPreservation aims to hold back microbes and enzymes and extend the edible period. Pasteurisation heats milk to about 72°C to kill pathogens and cools it fast; chilling at about 0–4°C slows bacterial growth; freezing below minus 18°C stops bacterial activity without killing the bacteria; canning sterilises with heat then seals the food away from air; drying and curing cut the water content or raise salt and sugar to suppress microbes. Raw or half-cooked items such as sashimi and soft eggs are high-risk foods and need extra care. For example, fresh meat from the wet market not cooked that day should be portioned and frozen; after thawing, cook it thoroughly and use it all at once — never refreeze.
7. Caring for kitchen aidsTime-saving and labour-saving aids make cooking far easier: egg beaters whip air into eggs and cream, grinders turn ginger and garlic into paste, and rice cookers control the cooking cycle automatically. Tools last only with correct use and care: wash and dry them at once after use, keep appliance cords out of water, avoid scratching non-stick coatings with metal spatulas, and keep knives sharp and stored safely. For example, rinse the hand blender with clean water running briefly straight after use — dried sauce is hard to remove later; never scrub the rice-cooker pot with steel wool, for a scratched coating makes rice stick, basic maintenance knowledge for every kitchen.

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8Recap Recap

• Cooking makes food safer, easier to digest and tastier, but nutrients can be lost — match the method to the ingredient
• Moist-heat methods (steaming, boiling, blanching, braising) use water or steam; dry-heat methods (stir-frying, pan-frying, deep-frying, baking, roasting) use hot air or oil
• Heat travels by conduction, convection and radiation; microwaves vibrate water molecules — never use metal containers
• Preservation holds microbes back: pasteurisation, chilling and freezing, canning, drying and curing each have their principle
• Wash and dry aids after use and maintain them well; with a work schedule, cooking is safer and faster