Bicarbonate of soda (aka. baking soda, bicarb soda, sodium bicarbonate)
Bicarbonate of soda is a pure leavening agent, which means it needs to be mixed with moisture and an acidic ingredient for the necessary chemical reaction to take place to create carbon dioxide and for food to rise. For this reason, it’s often used in recipes where there is already an acidic ingredient present, such as lemon juice, chocolate, buttermilk or honey.
Baking powder is made up of several elements, one of these being sodium bicarbonate, as well as an acid, cream of tartar and filler like cornflour to absorb any moisture.
As it comes pre-mixed with the acidic ingredient for you, all you need to add is the moisture. The acidic ingredient most often used in baking powder is cream of tartar.
You can make your own baking powder using this recipe: simply mix two parts cream of tartar with one part bicarbonate of soda.
When do I use baking soda and when do I use baking powder?
Most people cook with self-raising flour when a leavening agent is required, unless the specific qualities of bicarbonate of soda are required.
Bicarbonate of soda imparts a slightly different quality to that of baking powder when used in cooking. It can have a slightly 'tangy' taste and it makes a lovely golden colour. It also makes a very specific texture not achievable with baking powder. It is very important to sift bicarbonate of soda well as it gets lumpy and to use very exact measures as the 'tangy' taste can quite easily become bitter or soapy if too much is used.
Can I use baking powder instead of bicarbonate of soda?
This can be done in a pinch. If a recipe calls for 1 teaspoon of baking soda, you'll want to substitute with 2 to 3 teaspoons of baking powder.