3. Food Science

Cards (45)

  • Why is food cooked?
    • To make it safe to eat (destroys microorganisms)
    • To make it palatable - develops flavours, texture, colour
    • Extends shelf life
    • Makes it easier to digest
  • What are the three cooking methods?
    Wet (moist), dry, or fat-based
  • Examples of wet methods:
    • Boiling - softens - vegetables, rice, soup
    • Steaming - tenderises - vegetables, rice
    • Stewing
    • Poaching - tenderises - fish, chicken, eggs
    • Casseroling
    • Braising - tenderises, softens - meats, fish, vegetables
    • Simmering - tenderises, evaporates - stews, vegetables, curries
  • Examples of dry methods:
    • Baking - browns, crisps - cakes, pastries, potatoes
    • Roasting - browns, crisps - roast chicken, potatoes
    • Grilling/BBQ - chars, browns, crisps - bacon, toast, cheese
    • Dry frying - browns, crisps - bacon, lardons, chorizo, nuts
  • Examples of fat-based methods:
    • Deep frying - browns, crisps - battered fish, doughnuts
    • Shallow frying - sets, browns - eggs, onions, fish
    • Stir-frying - softens, reduces bulk - bean sprouts, sliced vegetables
  • Microwave cooking:
    • Uses a type of radiation called microwaves
    • These travel in straight lines and penetrate the food
    • The microwaves make water molecules vibrate, which creates friction, and therefore heat
    • Hot spots could occur, so food should be mixed
  • Three methods of heat transfer:
    • Conduction - solids
    • Convection - liquids (in air too, convection currents are made)
    • Radiation - air
  • Protein denaturation - the structure of amino acids are altered; they change shape or unfold because chemical bonds are broken.
  • Denaturation can be caused by heat, decreasing pH (more acidic), adding enzymes, or by mechanical actions.
  • Protein coagulation - a type of protein denaturation.
    • Starts at 60 degrees Celsius and finishes at 70 degrees Celsius
    • Examples are egg custard and quiches
    • Causes change in texture; runny eggs become coagulated (set)
  • Gluten formation occurs when water is added to a wheat flour to form a dough.
    • Wheat flour contains two proteins: glutenin and gliadin, which combine to form gluten.
  • Gluten in bread: makes the dough stretchy and elastic, kneading helps strengthen gluten, gives the bread structure
  • Gluten in pastry: Rubbing fat into the flour makes short gluten strands (shortening) which gives the pastry a rigid structure
  • Gluten in pasta: helps the pasta hold its shape, also makes the pasta dough flexible.
  • Enzymic browning - oxidation of the surface of cut fruit and vegetables. Cell enzymes react with the air, like in apples.
  • Enzymic browning can be prevented by:
    • Blanching cut fruits/veg in boiling water
    • Blanching veg before freezing
    • Dipping fruit/veg in acid, like lemon juice
    • Submerging in water
    • Cooking
  • Oxidation - causes discolouration. Also causes vitamins to be lost, and enables enzyme activity e.g. browning.
  • Gelatinisation - when starches swell to thicken liquids. Requires heat and stirring.
  • Gelatinisation in sauce-making:
    • 60 degrees Celsius - starch granules begin to swell and absorb the liquid
    • 80 degrees Celsius - starch grains burst and thicken the sauce
    • 100 degrees Celsius - starches complete thickening, the sauce is ready
    • Must be constantly stirred to prevent lumps and help heat transfer
  • High viscosity - very thick
    Depends on the ratio of thickening agent to liquid; more starch will result in a thicker sauce, and changes the consistency
  • Dextrinization - occurs when starch is toasted or cooked by dry heat
  • Starch is broken down by dry heat to form dextrins (a brown sugar)
  • Dextrinization is known as non-enzymic browning
  • Dextrinization gives the products a golden, brown look, with a sweeter taste and makes them crisp
  • Caramelisation - causes sugar to change colour due to dry or moist heat
  • Caramelisation causes surfaces to go brown on baked goods that have sugar in them
  • Caramelisation is also called non-enzymic browning
  • Caramelisation results in a golden colour, browning gloss, sweetness, and stickiness
  • Examples of caramelisation:
    • Frying onions
    • Making a crème brulee
  • Types of fat:
    • Fat from animal sources - butter, lard. These are saturated.
    • Fat from vegetable sources - margarine. These are unsaturated and are suitable for vegetarians and vegans.
  • Shortening - rubbing in fat to flour to give the pastry a crumbly texture. This prevents gluten formation.
  • Plasticity - the ability of a fat to change properties over different temperatures. Cold fats are solid and firm, room temperature fats are spreadable and soft, and warm fats melt and become runny.
  • Aeration - incorporating air into a mixture, which increases the volume of the product
  • Aeration helps products have a light and open texture; methods that help aeration are beating, whipping, creaming, and whisking.
  • When creaming fat and sugar together, aeration occurs, which makes the mixture become paler, and a foam is made.
    When baked, the trapped air expands, and the cake rises.
  • Emulsions - mixtures of liquids that don't normally mix, like oil and water
  • Emulsifiers have two ends:
    • Hydrophilic - water-loving - forms chemical bonds with water
    • Hydrophobic - water-hating - forms chemical bonds with oil
  • Hollandaise - a hot emulsion
    Mayonnaise - a cold emulsion
  • How to make mayonnaise:
    • Whisk lemon juice and egg yolks together
    • Pour some oil in gradually, keep whisking
    • If the emulsion looks too thick, add some water