Irish soda bread is a type of quick bread that relies on baking soda, not yeast, to rise. The bread contains buttermilk, which contains lactic acid. The acid reacts with the baking soda to create air bubbles, resulting in a perfectly risen dough.
Soda bread became incredibly common during the Irish Potato Famine, as you can make it with only four ingredients: flour, salt, an acid, and baking soda.
TIL, thanks