Question: How does self-raisng flour rise?

Fiona Hatch answered on 9 Mar 2012:

Self raising flour rises due to the baking powder inside.

Self raising flour is different from normal flour as it has baking powder mixed inside already. Baking powder is usually made up of a chemical called sodium carbonate, when mixed with water this will releases the gas carbon dioxide. So when you mix a cake together and pour it into a tin, the heat plus the water in the mixture will cause the baking powder to release small amounts of carbon dioxide which produces bubbles. These bubbles try to rise up and so the mixture starts to rise with all the tiny bubbles. The reason the air does not escape is because the heat from the oven is making the cake solid. Once is it solid the carbon dioxide slowly leaves the bread or cake, so don’t worry you’re not eating loads of carbon dioxide!!

If you look very closely to bread or a cake you can see the small bubbles left over from when the carbon dioxide was trying to escape. It is also the reason why bread can be so soft as you’re squeezing out the air!