Properties of Food: Carbohydrates (AQA GCSE Food Preparation & Nutrition)

Properties of food: carbohydrates

• Examples of carbohydrates in food include:

  • starch

  • sugars

• Carbohydrates can change during the cooking process, altering the appearance, texture and flavour of foods

Gelatinisation

• Gelatinisation aids thickening of liquids, e.g. in

  • gravy

  • soups

  • risotto and rice pudding

  • some custards

• Gelatinisation occurs when starch molecules in food are released from starch granules upon heating

• During the gelatinisation process:

  1. starch granules are mixed with water

  2. the application of heat breaks the bonds within starch molecules, allowing starch granules to absorb water

  3. the starch granules swell as they take on water

  4. the starch granules burst open and release starch into the surrounding liquid, causing it to thicken

Gelatinisation diagram

• Starch may be released from;

  • particles that are suspended within a liquid, e.g. cornflour or flour that is added to a roux or a béchamel sauce

  • solid foods that are cooked in a liquid, e.g. rice, pasta or potatoes

• The extent to which a liquid thickens due to gelatinisation depends on the ratio of starch to liquid in the mixture; the higher the starch to liquid ratio, the greater the thickening effect will be

• When liquids that have been thickened using starch are allowed to cool, the starch may set into a gel

Dextrinisation

• Dextrinisation causes browning of food, adding a crispy texture and sweeter flavour to, e.g.

  • bread

  • biscuits

  • pastries

• Dextrinisation occurs when dry heat is applied to starch molecules in food, e.g. during

  • baking

  • toasting

• During dextrinisation starch is broken down into smaller molecules known as dextrins

Dextrinisation diagram

• The extent to which dextrinisation occurs depends on the length of time for which the food is heated; a longer period of heating results in more dextrinisation

Caramelisation

• Caramelisation also causes foods to turn brown, and produces a sweet flavour; examples include:

  • fudge and toffee

  • crème brûlée topping

  • browning of vegetables during cooking, e.g. caramelised onions

• Caramelisation occurs when sugar, or food that contains sugars, is heated to a high temperature

• During caramelisation sugars are broken down and water is released

A Healthier Michigan, via Flickr

• Water can sometimes be added during caramelisation to reduce the risk of burning; burnt sugar gives food a bitter taste

• Note that meat and fish can also brown and taste sweet when heated, but this process involves proteins within the food and is slightly different to caramelisation