| As to baking soda as a leavening ingredient, without something acid in the mix to make the baking soda release carbon dioxide, it wouldn't do a thing. There are recipes with acidic ingredients such as buttermilk or lemon juice that can use some baking soda as a leavening ingredient, but even those still normally also require some baking powder (which has a second ingredient that turns acidic when wet). In this case, it's a sponge cake which has no leavening ingredient. Eggs whites are whipped until peaks form and when those are folded into the batter, they add a lot of very tiny air bubbles trapped in the whipped egg whites. Those air bubbles are what make a sponge cake rise. So baking soda has no place in this recipe. |