Since I don't like the taste of baking powder, I've been trying to substitute baking soda where possible. However, the last time I tried to bake a cake from scratch, the results were much less than perfect. In fact, the cake didn't rise at all. Though, I'm not completely positive that I added any baking soda at all.
This led to a discussion with one of my sons about why cakes rise. Since baking soda is a base, he decided that there must be some acid in the ingredients to react with the baking soda to produce bubbles and to make the cake rise and be "light".
After researching the subject on line, I found out that beating the shortening is the first step in adding air bubbles to a cake. (That's why one should beat the shortening and then gradually add the sugar.) Beating the egg(s) also produces small air bubbles. However, the main ingredients to produce the bubbles are the acid and base. Baking powder can be made by combining baking soda and cream of tartar and corn starch. Cream of tartar when dissolved in water produces an acid. When baking soda is added to this weak acid, bubbles of hydrogen are produced. The corn starch seems unecessary except for storage purposes.
So, if there is something acidic like sour milk, orange juice, or lemon juice in the recipe, one can substitue 1/4 t baking soda for 1 t baking powder -- though the recipe probably already calls for baking soda instead of baking powder. Otherwise, one can substitute 1/4 t baking soda plus 1/2 t cream of tartar for 1 t baking powder.
