Bicarbonate of soda

is an alkaline raising agent used in recipes that contain an acid ingredient such as buttermilk or lemon juice - ideal for soda bread. It is one of the ingredients of baking powder. It can be mixed with cream of tartar to produce a darkening effect in recipes containing chocolate, or in ginger cakes. Bicarbonate of soda can also help neutralise strong fruit acids like those in rhubarb or blackcurrants, alleviating the sour flavour.