Baking Powder (Best Option)
3 teaspoons baking powder per 1 teaspoon baking sodaBaking powder contains both an acid and a base, allowing it to react in liquid environments like soup to produce carbon dioxide gas, which can help with lightening the texture and balancing acidity. It mimics the leavening action of baking soda but is less potent, hence the higher ratio.
To use baking powder effectively in soup, measure carefully to avoid over-foaming or off-flavors. Since it contains acid, it may slightly alter the soup's pH and flavor profile, so taste testing is recommended.
Compared to baking soda, baking powder provides a gentler leavening effect and better flavor neutrality in soups, making it the most reliable substitute.