Mattisson Baking Soda – Natural Leavening Agent Baking soda is a 100% natural leavening agent. Baking soda does not contain additives such as this can be the case with baking powder. Baking soda promotes the volume of the baking mixture during baking. Dissolve the baking powder in two tablespoons of hot plant-based milk and mix it with the baking mixture. Baking Soda (Sodium bicarbonate..