Science of Food

• Cooking methods can be:

  • Water-based e.g boiling, steaming
  • Dry e.g baking, dry frying
  • Fat-based e.g deep frying, stir frying
• Three ways that heat is transferred through food:

  • Conduction
  • Convection
  • Radiation
• Conduction - heat is transferred through direct contact with heat source
• Convection - transfer of heat in currents throughout air or liquid due to hot air rising and cool air sinking
• Radiation - Heat energy passing in direct lines through air
• Protein denaturation:

  • Denaturation occurs when the amino acid chains in proteins unfold
  • Protein can be denatured by heat (cooking), lowering pH (adding acid), enzymes (adding them), mechanical actions (e.g whisking)
• Protein coagulation:

  • Type of denaturation
  • E.g custards, quiches
  • Causes foods to set
  • Irreversible process
• Gluten formation:

  • When water is added to a wheat flour to form a dough
  • Two proteins in wheat flour (glutenin and gliadin) combine to form gluten
  • Strong flour contains more gluten
  • Bread dough is made stretchy and structured by gluten
  • Rubbing-in method creates short gluten strands and shortens pastry texture
  • Gluten in wheat flour helps pasta stretch into different shapes and hold that shape
• Proteins and enzymes browning:

  • Occurs on the surface of cut fruits and veg e.g apples, potatoes
  • Due to oxidation of cell enzymes
  • Can be prevented by blanching, cooking, adding acid, submerging in water
• Oxidation:

  • Causes discolouration
  • Causes vitamin loss
  • Enables enzymes activity
  • Can be reduced by quicker cooking, quicker serving, less water used, keeping lid on when boiling
• Gelatinisation - When starches thicken liquids
• Gelatinisation in sauce making:

  • Starch grains absorb liquid and swell
  • At 80°C they burst and thicken the sauce
  • This completes at 100°C, so you must fully cook the sauce
  • The sauce needs starting to prevent lumps
• Gelatinisation and ratios:

  • Sauce is viscous, so it can either be poured or used to coat, or used to bind
  • Change in viscosity is due to the ratio of thickening agent to liquid
  • Retrogradation - the deterioration of a starch-based sauce
  • Synerisis - loss of fluid from a foam or set mixture
• Modified starches - Used to help gelatinisation occur in different ways e.g gravy granules
• Dextrinisation:

  • Occurs when starch is toasted or cooked by dried heat
  • Result of starch breakdown by dry heat to form dextrins
  • Aka non-enzymic browning
  • Adds flavour
  • Hygroscopic - absorbing water from the air
• Caramelisation:

  • Causes sugar to change colour and flavour due to dry or moisture heat
  • Causes surface browning on goods containing sugar
  • Aka non-enzymic browning
  • Turns sugar solutions into syrup
• Shortening:

  • Rubbing-in method
  • Fat coats flour grains, preventing gluten development
  • Causes cooked texture to be short and crumbly
• Plasticity:

  • Ability of fat to change properties over a range of temperatures
  • Cold - solid
  • Room temp - soft
  • Warm - melted
• Aeration:

  • Creates light and open texture
  • Beating/whisking causes fat molecules to trap air, creating a foam
  • Increases volume of mixture
• Emulsions - Immiscible (unmixable) liquids that are mixed
• Emulsifiers:

  • Hydrophilic end - forms chemical bonds with water
  • Hydrophobic - forms chemical bonds with oil
• Emulsions:

  • Oil in water (liquid) or water in oil (solid) emulsion
  • Stabilisers keep emulsions mixed
• Emulsification:

  • Requires agitation by whisking
  • Slow addition of oil
  • Helped by an emulsifier e.g lecithin (found in egg yolk)
• Raising agents:

  • Physical/mechanical
  • Chemical
  • Biological
• Physical/mechanical:

  • Mechanical - actions such as whisking, sieving
  • Physical - air, water vapour, steam (also need ingredients e.g egg, milk to act as a raising agent
• Physical raising agents:

  • Air pockets swell to increase volume
  • Steam is produced from the water in a mixture during cooking to aerate the product
  • Ingredients containing protein form foams, and sugar or cooking stabilises them
• Chemical raising agents:

  • Produce carbon dioxide when heated with a liquid
  • Cause fizzing and gas bubbles
  • E.g bicarbonate of soda, baking powder, self-raising flour
• Biological raising agents (yeast):

  • Ferments to give off carbon dioxide gas
  • During baking, the heat inactivated and kills the yeast, preventing any more growth
• Bacteria:

  • Single-celled organisms than can reproduce rapidly
  • Sometimes useful, sometimes harmful
• Conditions for bacteria growth:

  • Temperature: 5°C-63°C
  • Moisture needed
  • Time: they multiply every 10-20 mins
  • Nutrients: enjoy high-risk foods
  • pH level: neutral
• Yeast - helpful organism used as a raising agent
• Mould:

  • Type of fungus
  • Grow on many foods
  • Slightly acidic conditions
  • Need moisture and warmth
  • Live in fridge, not in freezer
• Cheese/yoghurt production:

  • Needs a starter culture of bacteria in some milk
  • These reproduce and convert lactose into lactic acid
  • This thickens the mixture
• Moulds can be used safely to create different types of cheese e.g blue, rind-washed, and soft ripened
• Salmonella:

  • Affects - raw meat, eggs, dairy
  • Symptoms - diarrhoea, vomit
  • Onset - slow
• Staphylococcus aureus:

  • Affects - cooked meat, dairy
  • Symptoms - diarrhoea, vomit
  • Onset - fast
• Clostridium perfingens:

  • Affects - meat products
  • Symptoms - diarrhoea, nausea
  • Onset - medium
• Clostridium botulinum:

  • Affects - incorrectly canned meat, fish, veg
  • Symptoms - paralysis, nausea
  • Onset - slow
• Bacillus cereus:

  • Affects - cooked rice, pasta, cereals
  • Symptoms - diarrhoea, vomit
  • Onset - fast
• Food poisoning bacteria (bacteria multiplying in food):

  • Salmonella
  • Staphylococcus aureus
  • Clostridium perfingens
  • Clostridium botulinum
  • Bacillus cereus