Cooking

• Physical changes during cooking

  1. Shrinkage

  2. Tenderising

  3. Nutrient loss

  4. Colour change

  5. Texture change

  6. Thickening
• Physical change: Shrinkage


  Protein foods, e.g. meat, shrink as protein coagulates, water evaporates and fat melts
• Physical change: Tenderising


  Collagen in meat connective tissue changes to gelatine, making meat tender and easier to digest
• Physical change: Nutrient loss

  Some B-group vitamins and vitamin C in vegetables are lost as they leach into the cooking liquid, decreasing the nutritional value
• Physical change: Colour change

  If overcooked, chlorophyll in green vegetables, e.g. green beans, will fade to an olive-green colour
• Physical change: Texture change

  Cellulose present in the cell walls of fruit and vegetables softens, making them easier to digest
• Physical change: Thickening


  Heat causes starch grains to swell and burst, absorbing liquid present to form a thickened sauce, eg. roux-based sauce
• Reasons why food is cooked:

  • Destroys microorganisms
  • Destroys enzymes lengthening shelf life
  • Destroys naturally present toxins
  • Makes food easier to digest
  • Improves appearance
  • Enhances flavour
• Destroy


  Can be harmful if eaten without cooking
• Destroy toxins naturally


  • Makes food (e.g. potatoes) easier to digest
  • Improves the appearance of food, eg red meat becomes brighter
  • Enhances the flavour of food, eg, meat, as fat melts and extractives concentrate
• Cooking causes physical and chemical changes in food
• Physical changes during cooking

  1. Shrinkage

  2. Tenderising

  3. Nutrient loss

  4. Colour change

  5. Texture change

  6. Thickening
• Shrinkage


  Protein foods, e.g. meat, shrink as protein coagulates, water evaporates
• Tenderising

  Collagen in meat connective tissue changes to gelatine, making meat more tender and easier to digest
• Nutrient loss

  Some B-group vitamins and vitamin C in vegetables are lost, as they leach into the cooking liquid, decreasing the nutritional value
• Colour change

  If overcooked, chlorophyll in green vegetables, e.g. green beans, will fade to olive-green colour
• Texture change

  Cellulose present in the cell walls of fruit and vegetables softens, making the food easier to digest
• Thickening

  Heat causes starch grains to swell and burst, absorbing liquid present to form thickened sauce, e.g. roux-based sauce
• Chemical changes during cooking

  1. Maillard reaction

  2. Caramelization

  3. Dextrinisation
• Maillard reaction

  The browning of food due to action between amino acids and reducing sugars. It produces a brown crust with an appealing flavour and aroma
• Caramelization

  The browning and sweetening of sugars when heated above 150°C, giving a deeper brown colour and sweet flavour
• Dextrinisation

  When starch foods are heated, the starch molecules break down to form dextrins. This causes colour changes and alters the texture of the food
• Methods of heat transfer in cooking

  • Conduction
  • Convection
  • Radiation
• Conduction

  The transfer of heat from molecule to molecule until all are heated
• Convection

  The transfer of heat by currents in a liquid or gas. When air or liquid is heated it expands and rises, with cold air or liquid falling to take its place, creating convection currents which cook the food evenly
• Radiation

  The transfer of heat directly from the source to the food
• Cooking methods

  • Frying
  • Boiling
  • Stewing
  • Baking
  • Steaming
  • Roasting
  • Grilling
• Many cooking methods involve more than one method of heat transfer, e.g. boiling uses conduction and convection
• Factors to consider when choosing a cooking method

  • Density/thickness of food
  • Time
  • Skill
  • Quantity of food to be cooked
  • Personal likes/dislikes
  • Equipment
  • Sustainability
• Moist cooking methods

  • Boiling
  • Poaching
  • Steaming
  • Stewing
  • Braising
  • Pressure cooking
• Dry cooking methods

  • Baking
  • Roasting
  • Grilling/barbecuing
• Frying methods


  • Shallow frying
  • Deep frying
  • Stir frying
  • Dry frying