Answer:
Bicarbonate of soda (also known as bicarb soda or baking soda) and baking powder are leavening agents used in biscuits, cakes and breads. Bicarb soda is a fine white powder, which fizzes when it comes into contact with acid. This fizzing releases carbon dioxide gas, which is responsible for the rising of cakes and breads, as well as the bubbly texture of soft drinks. When used in baking, bicarb soda is usually dissolved in liquid or sifted with dry ingredients.

Mixing it with acidic ingredients (such as honey or lemon juice) is required for it to perform its role in the leavening (rising) of foods. The reaction commences as soon as the bicarb soda is mixed with the acid. An example of this reaction is when bicarb soda is added to the melted butter and golden syrup mixture when making Anzac biscuits.

Baking powder is similar to bicarb soda, except that it has an additional ingredient added. Cream of tartar (an acid) is commonly added to bicarb soda to make baking powder. It works in a similar way to bicarb soda, by producing gas to make a product rise.

The main difference is that, in the case of baking powder, the acid needed to trigger this leavening reaction is already present in the powder, so it begins to react as soon as in comes in contact with any liquid (not necessarily an acidic one).

Baking powders usually have a mixture of ingredients, which allow reactions to take place in two stages. The first results in bubble formation when ingredients are mixed in the bowl, and the second occurs later when the product is baking, causing it to rise.

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Since these ingredients react differently, bicarb soda cannot be used to replace baking powder in a recipe. To make the equivalent of 1 teaspoon of baking powder, combine ¼ teaspoon of bicarb soda with ¼ teaspoon of cream of tartar and sift with dry ingredients. It is important to bake the product as soon as the mixture is prepared, as the reactions caused by baking powder commence as soon as it comes into contact with the liquid in the recipe.

This information is provided by the Sanitarium Nutrition Service.