Dough containing baking soda or baking powder (sponge dough, etc.) swells when heated because sodium bicarbonate dissolves in the water in the dough and undergoes a chemical change when heated to generate carbon dioxide.
● Baking soda: Since it is made only of sodium bicarbonate, it is only incompletely decomposed and the rate of carbon dioxide generation is low. Also, the sodium carbonate produced by this decomposition is alkaline and has a bitter taste. In addition, the flavonoid pigments in the wheat used in the dough tend to turn yellow in alkaline conditions, making it unsuitable for whitening dough.
● Baking powder: Improves the disadvantages of baking soda. Baking powder is made by adding several kinds of ingredients called acidic agents to baking soda, and is devised to completely decompose sodium bicarbonate and promote the generation of carbon dioxide gas. This suppresses bitterness and coloration.
Baking powder also contains cornstarch. The reason is to prevent the sodium bicarbonate and the acidic agent from contacting each other and reacting during storage. That is, it is put in as a blocking agent to prevent contact between the two.