Zesta Bicarbonate soda is an alkali used as a leavening agent. Zesta Bicarbonate soda is used in many foods from breads to cakes. Zesta Bicarbonate of soda needs to be combined with acid and moisture to activate its leavening ability; therefore it is often used in combination with cream of tartar, buttermilk, yogurt, and milk.When it is mixed with an acid, it produces carbon dioxide which provides the expansion in the mixture. When you cook the mixture, the carbon dioxide is then replaced with air and you have light, fluffy cake or loaf of bread.It is important that you use the required amount of zesta bicarbonate of soda to ensure that your cake doesn?t collapse and to make sure you are not left with an unpleasant flavor or greenish tinge in your food.