Raising agents work by incorporating a gas into a mixture. When you heat the gases they expand and rise relating a light and open texture.
Raising agents may be added by mechanical means such as sieving and beating or they can be included in the ingredients e.g yeast and bicarbonate of soda.
Raising agents are natural e.g air steam and yeast or can be chemical e.g bicarbonate of soda.
Natural raising agents
The three gases which make products light are; air, steam and carbon dioxide.
In most mixtures you use more than one raising agent.
You add air mechanically to food when whisking, sieving, beating, rubbing, rolling or folding.
Steam is a raising agent in mixtures with a high proportion of liquid, which are cooked at high temperatures. The water in the mixtures turns to steam.
Biological raising agents
Yeast is a micro-organism. When it reproduces it gives off carbon dioxide.
The following conditions are needed for reproduction:
Warmth: optimum temperature 25-28 degrees, too low slow rate of reproduction, too high it's killed
Food: sugar added to mixture or obtained from flour
Time: the mixture must be covered and left to rise in a warm place
Chemical raising agents
Chemicla raising agents produce carbon dioxide when there heated with a liquid
Self raising flour already has raising agents
Bicarbonate of soda produces carbon dioxide and washing soda when heated.
Bicarbonate of soda plus an acid e.g vinegar
Baking powder is a mixture of bicarbonate of soda and acid.