Bread soda, baking powder, and yeast are all leavening agents. Leavening agents all release the gas, carbon dioxide causing dough or batter to expand when heated. Carbon dioxide bubbles are what gives the light texture you want in baking.
(Yeast works by fermentation. Yeast cells convert cereal-derived sugars into ethanol and carbon dioxide, giving an additional tart flavour such as in sourdough bread).
Bread Soda/Baking Soda (Sodium Bicarbonate)
Irish soda bread rises due to the chemical reaction between bread soda, an alkali (base), and buttermilk, an acid, releasing carbon dioxide bubbles. Buttermilk is what is left over after churning cream to make butter. This chemical reaction is immediate, therefore the dough must be put in the oven quickly before the carbon dioxide bubbles break up and disappear! We don’t want a flatbread! Bread soda is used for “quick” recipes for breads and biscuits. There is no waiting around like there is for yeast to do its thing. ( just had a COVID flashback!)
Baking Powder ( Cream of Tartar)
Baking powder contains both the alkali and the acid required for the chemical reaction to produce carbon dioxide bubbles. Therefore Baking Powder contains both bread soda and an acidic salt, typically cream of tartar ( potassium acid tartrate). Baking powder also contains cornstarch which acts as a buffer, preventing activation between acid and alkali during storage.
When the baking powder dissolves in liquid the bread soda reacts with the cream of tartar to get those air bubbles we want! No need for an acid ingredient such as buttermilk.
Baking Soda and Baking Powder go off in the cupboard and may explain why your baking didn’t rise!
They may need to be replaced every three months if you are not baking regularly.
Give it a go and enjoy!