Baking powder is a raising agent that is commonly used in
cake-making. It is made from an alkali, bicarbonate of soda, and an
acid, cream of tartar, plus a filler like cornflour or rice flour which
absorbs moisture.
The powder is activated when liquid is added,
producing carbon dioxide and forming bubbles that cause the mixture to
expand. For this reason, it is important to get your cake mixture into
the oven quickly once the 'wet' ingredients have been added to the 'dry'
ingredients.
Self-raising flour is made from plain flour combined with a small amount of baking powder.
