Raising Agents (AQA GCSE Food Preparation & Nutrition)

Cooking with raising agents

• The role of a raising agent is to cause a mixture to rise; this is achieved as follows:

  1. bubbles of gas are introduced into a mixture

  2. heating causes the gas to expand and the mixture rises

  3. the resulting air pockets within the cooked mixture produce a light, airy texture

Raising agents diagram

• Examples include:

  • chemical raising agents

  • mechanical raising agents

  • steam

  • biological raising agents

Chemical raising agents

• Chemical raising agents react to produce the gas carbon dioxide; it is this gas that causes the mixture to rise

• Chemical raising agents include:

  • bicarbonate of soda

    • Bicarbonate of soda releases carbon dioxide when it is heated in the presence of liquid and an acid

    • It has a soapy flavour due to its alkaline nature, so tends to be used on its own only in strongly flavoured items, e.g.

      • soda bread

      • gingerbread

      • fruit cake

  • baking powder

    • Baking powder contains bicarbonate of soda and cream of tartar; the acidic cream of tartar neutralises the alkaline baking soda, removing the soapy flavour

    • It can be added as an ingredient to baking mixtures, and is also present within self-raising flour

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Mechanical raising agents

• Mechanical raising agents work to trap air within a mixture; this air then expands during cooking and causes the mixture to rise

• Methods of trapping air within a mixture using mechanical methods include:

Steam

• When food is cooked, heat causes water within it to boil and turn into steam

• In foods with a high water content the rising steam can cause the mixture to puff up, e.g.

  • yorkshire pudding batter

  • choux pastry dough

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Biological raising agents

• Yeast is a living organism, so is referred to as a biological raising agent

• Yeast functions as a raising agent as follows:

  1. yeast is added to the dough and the dough is left in a warm place for a period of time known as proving

  2. during proving the yeast begins to respire using sugar in the mixture as its fuel; this produces carbon dioxide gas as a waste product

     • Once the yeast cells run out of oxygen they start to produce alcohol as an additional waste product; this anaerobic process is known as fermentation

  3. the carbon dioxide gas causes the dough to rise

  4. heat during baking causes the gas to expand further and increases the rise

     • Baking kills the yeast and also causes any alcohol that may have been produced during proving to evaporate

• For a biological raising agent to function effectively the following are required:

  • the dough must contain liquid so that a gluten network can form

  • the environment must be warm enough for the yeast cells to respire at a high enough rate, e.g. 25-29 °C

  • sugar must be present in the dough to provide fuel for the yeast

• Examples of foods that are produced using biological raising agents include:

  • bread

  • doughnuts

  • croissants

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