Chapter 3: Cooking Methods

To make food safe to eat: High-risk foods must be thoroughly cooked to destroy food poisoning bacteria and natural poisons.

To develop flavour

• Cooking causes chemical reactions in food that develop flavour.
• Cooking concentrates flavour by causing water in food to evaporate.

To improve texture and appearance 

• Starch granules swell and gelatinize causing food to thicken or soften.
• Meat is tenderised.
• Fats melt and give smooth ‘mouth-feel’.
• Plant cells soften – vegetables and fruits become tender.Raw doughs rise and become light in texture.

To improve shelf-life of food: Cooking destroys micro-organisms and preserves foods.

• Atoms in metal pans and baking trays start to vibrate as heat energy from cooker goes into metal.
• Vibrations transfer heat energy to other metal atoms.
• Metal gradually heats up and passes heat energy to food.
• Metals are good conductors of heat – very good for baked products.
• Plastic, wood, air, thick cotton and wool are good heat insulators (poor conductors of heat) – used for pan handles and oven gloves. Wooden spoons to protect hands.

• When a pan of water is heated, heat is conducted through the metal pan to water molecules.
• Water molecules move upwards then downwards in a circular motion (convection currents) taking heat energy with them and passing it into the food.
• The more heat energy, the faster the water molecules move in circular convection currents.Also, happens in an oven with hot air currents.
• Gas oven/ordinary electric oven – zones of heat: hotter at the top than bottom shelf due to convection.
• Electric fan ovens – heat evenly distributed by fan – same temperature on each shelf.

• Grilled/barbequed food heated by radiant heat.
• Infrared heat rays heat the surface of the food and are absorbed.
• Food must be no more than 3.5cm thick otherwise may be undercooked inside.
• Food must not be too close to grill or it may burn easily.

• Water used to transfer heat.
• Boiling, braising, poaching, simmering, steaming, stewing.
• Heat transfer: conduction → convection.

• Starch absorbs water and gelatinises.
• Proteins denature and coagulate – become solid.
• Fat melts.
• Water evaporates – sauces reduce.
• Vegetables, fruits, pasta, rice, etc. tenderise.
• Meat tenderises (collagen converts to gelatine) – can become indigestible if overcooked.
• Colours change – e.g. meat from red to brown; vegetables bright green.Flavour intensifies.
• Vitamins B1, B2 and C dissolve in water and are gradually destroyed by heat.
• Vitamins B1, B2 and C can be conserved by preparing, cutting, grating, squeezing and cooking just before serving; using only a little water; limiting their exposure to light and oxygen; serving as soon as they are cooked.

• Oil used to transfer heat.
• Sautéing, shallow/pan frying, stir frying: conduction.
• Roasting, deep fat frying: conduction → convection.

• Intrinsic sugars caramelise and make food go golden colour.
• Flavour of foods intensifies as water evaporates.
• Starch absorbs oil and swells.
• Vegetables/fruits soften.
• Protein denatures and coagulates.
• Foods become crisp on outside – especially if coated with egg and breadcrumbs to protect food.
• Meat shrinks and squeezes out juices.
• Energy density of food increased.
• Vitamins B1, B2 and C are gradually destroyed by heat.

• Dry heat used to transfer heat
• Baking: convection → conduction.
• Grilling: radiation.
• Dry frying: conduction.

• Gases from raising agents to expand and make food rise.
• Protein denatures and coagulates – overcooking makes it less digestible.
• Meat proteins in muscle cells shrink and squeeze out juices.
• Free sugars melt and soften gluten in the flour. 
• Sugars caramelise.
• Fat melts and is released from meats – reduces energy density.
• Starch granules absorb water/fat and swell and soften.
• Gluten stretches as doughs rise then sets around gas bubbles.
• Starch on outside turns to dextrin and goes golden brown.
• Starch becomes more digestible.
• Flavours intensify.
• Vitamin B1, B2 and C destroyed by heat.

• Radiation: cooking by electromagnetic waves that vibrate water molecules and transfer heat energy very quickly.

• Protein denatures and coagulates quickly – will quickly overcook and become indigestible.
• Fat melts.
• Sugar caramelises and will burn easily.
• Starch gelatinises.
• Juices and water from meat are easily squeezed out.
• A little damage to vitamin B1, B2 and C.