Food Preparation and Preservation: Methods, Hygiene and Kitchen Safety
Questions here mix science (why food spoils, what cooking does to nutrients) with practical safety (kitchen hazards and first aid for a burn).
Cooking methods and nutrient loss
Boiling, steaming, pressure cooking, shallow and deep frying, baking, roasting, grilling and solar cooking. Vitamins C and the B-group are fragile: they are lost by heat, by leaching into water and by oxidation. Rules: wash vegetables before cutting, cut into large pieces, use minimum water and reuse the water, cover the pan, avoid overcooking, and never add baking soda, which destroys thiamine and vitamin C. Steaming and pressure cooking conserve more nutrients than boiling and draining.
Why food spoils
Microorganisms (bacteria, moulds, yeasts), enzymes, oxidation, moisture, heat, light, insects and rodents.
Preservation methods
- Drying and sun drying remove moisture.
- Salting, sugaring, pickling in vinegar, oil or lemon lower water activity and pH.
- Refrigeration and freezing slow microbes; they do not kill them.
- Canning and bottling use heat sterilisation plus a seal.
- Pasteurisation: 63 degrees C for 30 minutes or 72 degrees C for 15 seconds, then rapid cooling.
- Smoking, permitted preservatives, and airtight storage.
Kitchen hygiene and safety
Wash hands with soap, keep raw and cooked food apart, cover food and water, keep the bin covered, scrub the cutting board. Safety: turn pan handles inward, use dry hands on electrical switches, keep the cylinder valve closed, never leave hot oil unattended. For a burn, cool under running water for 10-20 minutes and cover loosely; do not apply toothpaste, oil or turmeric.
Worked example
A lemon pickle keeps for months because lemon juice and salt lower the pH, salt ties up water so microbes cannot grow, oil seals out air, and spices such as mustard and turmeric inhibit growth. Reasoning follows moisture, pH and oxygen in order.
Traps
Refrigeration does not sterilise; soaking vegetables for long leaches vitamins; baking soda brightens greens but destroys nutrients; hot water sets protein stains.