3.3 Food Science

• Why food is cooked

  • To make it safe to eat by destroying microorganisms
  • To change raw food to cooked food
  • To make it palatable by developing flavors, improving mouthfeel and texture, reducing bulk, improving color
  • To extend shelf life
  • To make it easier to digest
  • To allow variety to the diet
• How food is cooked

  1. Using heat to change texture, flavour and color of food

  2. Wet methods: boiling, steaming, stewing, poaching, casserroling, braising

  3. Dry methods: baking, roasting, grilling

  4. Fat-based methods: frying, stir-frying

  5. Pre-cooking methods like marinating can improve tenderness and flavour
• Factors affecting choice of cooking method

  • Type of food
  • Time available
  • Skill and facilities
  • Desired characteristics
  • Conservation of vitamins
• How heat is transferred to food


  • Conduction: heat transferred by contact of heat source to pan to food
  • Convection: heat transferred by currents which occur as heated air/water rises and cooler air/water falls
  • Radiation: heat energy passing in direct lines to food
• Protein denaturation


  • The structure of amino acids in proteins are altered, causing the protein molecule to unfold or change shape
  • Can be caused by heat, pH changes, or enzymic action
• Protein coagulation

  • A type of protein denaturation that is irreversible and causes loss of solubility
  • Occurs between 60-70°C
• Gluten formation

  • Gluten is formed when water is added to wheat flour (glutenin + gliadin), making the dough stretchy and elastic
  • Kneading helps align the gluten strands
  • Rubbing fat into flour makes short gluten strands
  • Gluten forms the structure in baked bread, pastry and pasta
• Dextrinisation

  • The breakdown of large starch polysaccharides into smaller dextrins when starchy foods are exposed to dry heat
  • Dextrins taste sweeter and add flavour to toasted, charred or baked goods
• Caramelisation


  • The browning and flavour change that occurs when sugar molecules are exposed to high heat and break down
  • Causes surface browning on baked goods containing sugar
• Aeration

  Helps create a light and open texture by trapping air in mixtures, e.g. creaming fat and sugar
• Shortening

  The process of using fat to create a characteristic short, crumbly texture

  Flour particles gain a waterproof layer when coated in fat
• How does a fat shorten a pastry mixture?

  • Fats with plasticity are good shortening agents because they rub in easily
  • Fat coats the flour grains, preventing gluten development
• What happens during the cooking of pastry?

  1. The flour grains absorb the fat

  2. The pastry sets from pliable to rigid (the gluten sets)

  3. Pastry turns golden brown
• Plasticity

  • Ability of a fat to change properties over a range of temperature (important factor)
  • Cold fats are solid and firm; fats at room temp. are spreadable and soft; warmed fats melt and become runny
  • Plasticity is made from the mixture of triglycerides, each with their own melting-point
• Emulsion

  • Mixtures of liquid that do not normally mix (known as immiscible liquids)
  • We need to keep stirring or shaking oily water so that the emulsions don't separate
  • Stabilisers keep emulsions mixed, preventing them from separating
• Emulsifier

  • Emulsifiers have a hydrophilic end (water-loving) that bonds with water molecules
  • Emulsifiers have a hydrophobic end (water-hating) that bonds with oil molecules
  • Natural emulsifier called lecithin, found in egg yolk (helps with emulsification)
• Process of emulsification

  1. Requires agitation by whisking, by mixer or food processor

  2. Slow addition of oil to prevent from separating

  3. Stable: mayonnaise; unstable: vinaigrette dressing

  4. Hollandaise: not emulsion; mayonnaise: cold emulsion
• How do raising agents work?

  1. Causes rising within foods, especially baked goods

  2. They create gas, air or steam which expands when heated and causes the food to rise

  3. Heating causes the molecules in the air to move more rapidly and apply more force

  4. This results in a light and airy texture within foods
• Chemical raising agents

  • They produce carbon dioxide when heated with a liquid
  • They cause fizzing and bubbling of gas
  • They must be carefully measured
• Bicarbonate of soda/baking soda

  • It is an alkali powder
  • Reacts with an acid (in the presence of water) to produce carbon dioxide, which causes bubbles which expand and causes rising
• Baking powder

  • Contains bicarbonate of soda and cream of tatar
  • As baking powder already contains an acid, only water needs to be added
  • Heating baking powder sparks a neutralisation reaction
• Self-raising flour


  Floor that already contains baking powder
• Biological raising agent

  • Yeast is a microorganism that is used to help bread rise
  • Fermentation in yeast is a biological raising agent
  • Yeast releases carbon dioxide and alcohol through the process of fermentation
• Conditions for yeast fermentation

  • Warm temperature (25-35°C), moisture, carbohydrates
  • Temperatures above 60°C during baking will inactivate and destroy yeast cells and end the fermentation process
• Ingredients affecting action of the yeast

  • Salt: excess will slow the action of the yeast
  • Fat: slows the action of the yeast
  • Sugar: speeds up yeast growth
• Steam

  1. When liquidy mixtures are cooked in hot ovens and water escapes as steam

  2. The rising of steam helps raise the mixture

  3. The mixture bakes and solidifies as water escapes

  4. If any cold air that gets added (from opening the oven door will sink the mixture

  5. This produces light and open texture with large pockets of air left after the steam is escaped

  6. It is used in choux pastry, popovers, yorkshire pudding
• Physical raising agent

  • We can fold air into doughs and mixtures
  • Folding pastry doughs into layers allows air to get trapped in between folds
  • Using the folding technique
  • Sieving ingredients like flour traps air between individual particles
  • Creaming adds air (egg whites stretch and unravel to trap air to form a gas-in-liquid foam)
  • Rubbing fat into flour introduces air between individual particles
  • Beating adds air to mixtures very rapidly
• Enzymatic browning

  • The discolouration of a fruit or vegetable due to the reaction of enzymes with plant cell substances and oxygen from the air (oxidation)
  • Happens on the surface of certain fruits and vegetables after being cut
• Preventing enzymic browning

  1. Acid-denatures enzyme proteins (e.g. lemon juice)

  2. Cooking-denatures enzyme protein

  3. Cold water-prevents reaction with oxygen in air

  4. Blanching before freezing-denatures enzymes + freeze state
• Oxidation

  • When substances combine with (pick up) oxygen
  • Causes vitamins to be lost (particularly vitamin C.)
• Reducing oxidation

  1. Use quicker, shorter method of cooking and keeping lid on when boiling

  2. Serving vegetables immediately after eating
• gelatinisation

  • starch grains absorb liquid, well, burst at (80C) and thickens the mixture, the starches complete thickening at just (under 100C)
  • the mixture needs heat and agitation (convection) to prevent lumps forming, stopping the mixture from sticking to the bottom of the pan and helps heat transfer (conduction)
• factors that affect protein denaturation:

  • heat: the structure of amino acids changes shape after cooking; the protein molecules uncoils when it is cooked with heat
  • pH: reducing the pH by using marinades such as lemon or vinegar to denature proteins
  • enzymes: enzymics are in the form of papain (papaya) and bromelain (pineapple)
  • mechanical actions: whisking egg white denatures the protein by uncoiling and unfolding because the foam formation occurs (gas in liquid) —> partially reversible change