• Protein molecules are very big and formed into bundles held together by chemical bonds.
  • Chemical bonds can be broken by heat, whisking, acids, air bubbles.
  • If a protein molecule bundle unfolds and changes shape – it denatures.


  • Denatured protein molecules unfold and join up with other ones to form big groups – they coagulate.
  • As they coagulate, they trap air and water.
  • Overcooking causes the coagulated protein molecules to tighten up and squeeze out water.


  • Protein in wheat flour formed when water is added to flour.
  • Gluten makes the dough stretchy, elastic and able to be shaped.
  • The dough will shrink back when it is stretched.
  • Gluten sets in the oven and traps gas bubbles that have been produced in the dough.
  • Pastry dough should be rested to allow the gluten to relax so it does not shrink fast in the oven.


  • Air is trapped in a gas-in-liquid foam by whisking, e.g. egg whites for meringue or eggs and sugar for whisked sponges.

How micro-organisms are used to make:

  • Non-pathogenic (safe) bacteria and moulds used in cheese making.
  • Bacteria culture turns lactose in the milk into lactic acid.
  • Lactic acid adds flavour, texture and preserves cheese.
  • Rennet added – turns milk to curds (solid) and whey (liquid).
  • Whey drained off.
  • Curds cut up, salt added, then curds are pressed.
  • Bacteria ripen the cheese to develop flavour.
  • Cheese left to mature for a few weeks.
  • Blue cheeses have a safe mould added to produce blue veins and flavour.


  • Yeast used to produce carbon dioxide gas to make the bread rise by fermentation.


  • Special bacteria culture added to milk.
  • Milk held at 42°C – bacteria ferment the lactose sugar to lactic acid.


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