Why, America of course. What, you thought it was Irish? Perish the thought! It was Native Americans who first invented chemical leavening, using ashes as they did to “lighten” grain cakes. How did that work? you might ask. Well, ashes contain alkaline salts. Put them into a wet grain porridge and the result will be bubbles. Not a lot of bubbles mind you, but enough to make a difference in the cooked porridge cake’s texture. Of course the flavor is another matter, but that didn’t seem to bother the Indians much.
It wasn’t until the mid-1700’s that colonists in the Americas caught on to what the locals were doing. Those were the days when chemists first isolated potassium carbonate (the alkaline salt I mentioned) from wood ashes, and realized that it could be safely used to leaven breads when combined with water or an acid like sour milk or diluted hydrochloric acid. The technique quickly caught on in the colonies and soon after in Ireland, where the natives faced similar bread-making challenges: a lack of bread ovens, baking know-how and a steady supply of the finely ground, hard (gluten-rich) flour you need for yeast-leavened bread.
Chemical leavening was a relative no-brainer. It was easy to mix and could raise even the most stubborn rough-ground grain paste into something resembling bread. Better yet, you didn’t need an oven (a brick oven or a kettle “Dutch” oven) to use it. Chemically-leavened breads would rise on a skillet. What’s not to like? The idea caught on all over the British Isles in the 1830’s and 1840’s but nowhere more so than Ireland, which is why these days, at least in America, we call it “Irish” soda bread.