Raising Agents

Food Preparation & Nutrition: AQA GCSE, topic 3.2.3

Raising Agents - Carbon Dioxide

Raising agents help cakes to 'rise' by producing gas which expands in doughs and mixtures when they're heated. Some agents add carbon dioxide.

Bicarbonate of soda is an alkali raising agent that breaks down when it's heated. Carbon dioxide bubbles form and, when they expand, cause a mixture to rise.
Baking powder contains both bicarbonate of soda and an acidic substance called cream of tartar. Heating baking powder sparks a neutralisation reaction.
Self-raising flours are made up of baking powder and plain flour.

Yeast is a microorganism that's used to help bread dough rise.
Yeast releases carbon dioxide and alcohol through the process of fermentation.
We usually have to prove doughs that contain yeast. This involves letting them stand in a warm environment to let fermentation happen.
During the proving process, the carbon dioxide that's released gets trapped and the dough rises.
When the dough is baked, the high heat kills the yeast and ends the fermentation process. Baking causes the carbon dioxide in the dough to expand (and the bread to rise) and the alcohol to evaporate.

Raising agents help cakes to 'rise' by producing gas which expands in doughs and mixtures when they're heated. Some agents produce steam or air.

When very liquidy mixtures (e.g. Yorkshire puddings) are cooked in hot ovens, water escapes as steam. The rising steam helps to raise the mixture.
The mixture bakes and solidifies as water escapes.
Any cold air that gets added (e.g. from opening the oven door) will sink the mixture.

We can fold air into doughs and mixtures by:
Literally folding pastry doughs into layers. Air gets trapped between folds.
Using the folding technique for mixtures. This involves using a spatula or spoon to cut through the mixture and pour it over itself to trap air.
Sieving ingredients like flour traps air between individual particles.
Creaming adds air.
Rubbing fat into flour introduces air between individual flour particles.

Beating adds air to mixtures very rapidly. Beating involves mixing ingredients with a spoon or fork.
If a whisk is used, we call this process whisking.