proteins and carbohydrates

• denaturing

  • Chemical bonds hold proteins' complex structures together. These break down during cooking, causing proteins to denature. 
  • Proteins fall apart and change shape. This is often an irreversible transformation.
  • Things that cause proteins to be denatured include:
  • Temperature changes.
  • Acidic substances (e.g. fruits like kiwifruit, mango, pineapple and fig are good at breaking down meat proteins).
  • Agitation (beating or whisking).
• coagulation

  • When denatured, protein molecules bang into other protein molecules and join together (coagulate). When this happens, water gets stuck between the protein molecules.
  • Coagulation alters food texture and how it looks - e.g. egg white transforms from a clear liquid into a white solid. 
  • Coagulation can help things stick together - e.g. when eggs are mixed with breadcrumbs.
  • Too much coagulation can be problematic. The food becomes dry and chewy as the protein tightens and water is pushed out of the molecules.
• foams

  • Chocolate mousse and meringues are examples of foams. We make them by trapping gas inside liquids.
  • When we agitate liquids storing protein (e.g. by whisking or beating), we cause the liquids' proteins to denature. The denatured proteins expand, trapping air in the liquid.
  • Then, when coagulation happens the air gets trapped and a foam is formed.
  • Over-beating or over-whisking will break coagulation bonds, causing the air to escape and the foam to fall apart.
  • When some foams are cooked, they become solid (e.g. egg white foams → meringues).
• starch gelatinisation (cont.)

  • Cooling the liquid turns it into a solid gel, which can be used for desserts which require set fillings (like key lime pie). 
  • Gelatinisation occurs when cooking spaghetti and other forms of pasta - the strands expand, become soft and starch is released into the liquid.
• dextrinisation

  • Dextrinisation describes the process of starch molecules breaking down into dextrins (smaller molecules) when starchy foods are exposed to dry heat. 
  • The process causes food to brown, develop a crispier texture and taste different.
  • Cooking time affects how dark and crispy the food turns. The longer the cooking time, the browner and crispier the food becomes.
• caramelisation

  • Caramelisation occurs when sugar molecules are exposed to high heat - they break down, the sugar browns and its flavour changes.
  • There are different stages of caramelisation:
  • Initially, the liquid is sweet-tasting and runny.
  • The liquid thickens with time and develops a caramel-like texture.
  • The liquid eventually hardens and develops a candy-like texture as it cools.
• caramelisation (cont.)

  • It's often necessary to add water at the start of the heating process to avoid burning the caramelised sugar. Once caramelised sugar starts to burn, it turns brittle and black.
  • Caramelisation adds sweetness. 
  • Some desserts are therefore caramelised (e.g. creme brulee) as well as some savoury foods, like shallots.
• role of gluten

  • Gluten is a form of protein. Wheat flours contain gluten. 
  • We get gluten by mixing water and flour to form dough. 
  • Gluten molecules can bend and stretch - we say they are coiled. This is why dough is stretchy.
  • We knead dough to lengthen, strengthen and stretch the gluten strands - this is called 'working' the gluten.
  • Gluten coagulates at high temperatures, while dough remains stretched. As a result, foods, such as well-risen bread, gain an airy texture.
• starch gelatinisation

  • Starch gelatinisation thickens starchy foods, like pasta sauces and gravy.
  • Starch granules hang in liquid until they're heated. The intermolecular bonds begin to break and water is absorbed. This causes the starch granules to soften and expand (swell).
  • The starch granules start to burst once temperatures reach 62°C-80°C. Starch is released into the liquid. 
  • The liquid is thickened by the addition of starch. The more starch that is released, the thicker the liquid becomes.